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Thread: SCAR vs AR; A detailed look...

  1. #1
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    SCAR vs AR; A detailed look...

    Part 1

    A little background information is in order first. I do contract reliability/predictive Maintenance work in many different industrial plants in the Southeast. I work for a family owned business and I have been in this field for about 13 years. I have access to several different types of test equipment that are not used by a lot of gun makers. I am sure the bigger companies have/use this type of equipment, in fact I highly suspect FN made use of this type equipment for design of the Scar, but the smaller ones probably do not. I have had the benefit, pleasure, and honor of training under some of the best names in the business in recent years. I have attended (and recommend anyone who is a student of the AR to take) Dean Caputo’s AR Diagnostic class and a couple of Pat Rogers’ carbine courses. From these and a few others (such as LAV and Magpul Dynamics), I have a good grasp of the function and operation of the AR. I am by no means an expert on anything, so don’t take any of the following as THE answer. It is just my opinion, from some things I have observed. I am in no way affiliated with anyone selling any of the products discussed below. I am not trying to sell any products myself. I am just looking at and testing some of my firearms then posting my observations. A review that is a little bit above and beyond the normal “fit & finish/average group size” reviews so often encountered.

    I have long been a fan of the Stoner/AR type rifle and own several quality pieces. In opening, I believe the Stoner system is a very viable system. It has been around for decades and to date, most of the shortcomings of this system have been identified and many have been addressed as best they could be. Parts are easily obtainable, maintenance procedures are commonly known, and the manual of arms is ingrained in many dedicated users. Some say newer is not necessarily better. I have mixed emotions about that statement. If a new product is made just for the sake of making something new to introduce to the market, most times it is a disappointment. If a company goes at it with the true desire to make a product that brings forth new technology, or improves on existing technology and ups the standard, does their “homework” during designing and testing phases, lots of times a better mouse trap is the fruit of their labor. There has been much debate recently with the stories on the web about the Mk16’s future role in the military. One re-occurring statement is that the Mk16 does not do anything better than the M4. That particular statement was what got me started on all of this. On what basis is this statement made? I realize that making contact with a target at 300m is an easy feat for both weapons. I realize good or bad, both are just 5.56mm weapons. I also realize the needs of the military, LE, and Citizen are all different, with some overlapping common needs. I also can see things from the prospective of the military, with thousands of M16/M4 weapons already in the system. I tried to base my approach on simply looking at machine A and comparing it to machine B and machine C. From what I have observed, I believe the statement of the M4 can do everything the Scar can is not entirely true. In fact, I believe there are things the Scar can do, that currently the M4 cannot. Those differences are listed below.

    I recently picked up an FN SCAR 16s from GT Distributors (who has a hell of a price on them BTW). Looking it over with an eye for finding fault in and troubleshooting machinery, I have to say thus far I am quite impressed. Making a reliable machine involves many factors. One of the biggest IMHO with firearms is timing. The proper timing of the parts working together to accomplish a given task is crucial for success. I sat down with my training Colt 6933 and my SCAR and stripped them both down to basic parts. One of the first things you notice is the weight difference in the bolt carriers. The scar is significantly heavier than the Colt M16 carrier. The buffers tested for the AR were H-buffer at 3.7oz, H-2 buffer at 4.5oz, and H-3 Buffer at 5.3 oz.


    The way I see it, this is a plus for the Scar. This allows the Scar to use the momentum of moving mass over spring tension as a means of feeding a new round into the chamber, or more so make use of the heavier mass in reliably feeding rounds into the chamber. One can look at the difference in the AR versus the Scar action spring and see what I mean.

    We all know that keeping an in-spec action spring in an AR, especially a short barreled AR, is essential to proper weapon function. This is a lot of times less critical in such rifles as the AK, and I think, key word “think”, having a “fresh” action spring will prove less critical in the Scar as well. The heavier carrier can also help in perceived recoil as well, one of the things I feel keeps the Scars muzzle rise down. It also slows the firing rate, and in my book is another plus.

    Next we look at the cam pin “travel” slot. You will notice this slot on the AR to be very short and abrupt when compared to the Scar. The slot on the AR is 0.6440” in full travel length with my well used calipers, and the slot on the Scar is 1.082. That is a drastic increase in the time it takes to unlock the bolt on a Scar versus an AR. One will also notice the slot on the Scar is more gradual in twist. The AR bolt starts to unlock almost immediately when the carrier moves to the rear. The Scar carrier moves almost an entire half inch before the bolt starts to unlock. What does this do? It allows for a little bit longer period of time before the bolt unlocks and removes the spent cartridge. Why is this beneficial? It allows the cartridge more time to cool back down and shrink from its expanded state against the chamber walls.




    Yet again, this is another big plus for reliability in my book. The cam pin on the AR and the Scar are very close in diameter, but looking at the bolt on each, the Scar has more metal surrounding it at the cam pin (0.1320” vs. the 0.1045” of the AR).

    I know there is a lot of talk about the heat introduced into the BCG of the AR and whether or not it is detrimental. As you will see, this area of the AR bolt, which is a common failure point, should probably be more substantial. I also wonder if having a cam pin that traverses completely through the bolt, and has a second travel slot cut out in the other side of the carrier would be beneficial? Maybe step it down on one side so it can only be inserted one direction, but have its own support on the opposite side of the bolt. This would help the pull to just one side, as in the AR where over time you get uneven wear on the bolt and cam pin, sometimes leading to cam pin hole failure. This is probably not possible in the AR as the cam pin sits vertically, but could be done in the Scar as the cam pin sits horizontally.

    In just about every dimension the bolt is bigger on the scar, except for the depth that the case sits inside the bolt. The extractor on the Scar is 0.276”, where as the AR is 0.244”. That is a 13% increase in the extractor size. Also, as pointed out to me by a very well know gun machinist and the go-to man for chromed lined barrel cut downs, the ejector on the SCAR bolt is chamfered around the edges to reduce the amount of brass on the cartridge being shaved off during operation.


    The firing pin retaining pin on the AR is another problem part for some. I had a Colt BCG that chewed them up every few hundred rounds. Turns out it was an out of spec carrier, but for those that run a suppressor this can be a trouble area in the system. The AR’s FPRP is 0.0860” in diameter, while the Scar is 0.2030”.

    Last edited by Hootiewho; 09-29-10 at 05:08.

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    Part 2

    Since we are on the BCG/Moving Parts Assembly, let’s go ahead and talk about heat. I took my Scar, my Colt 6933 (which has been modified with the BCM extractor spring upgrade, H3 buffer, KAC URX Rail system), a good friend’s LWRC 16” 5.56mm M6 piston AR, and a Norinco 7.62mm AK to the range along with our FLIR handheld IR camera. The outside ambient temperature was high 70’s/low 80’s at this time. I took 4 magazines loaded with 28 rounds each of Federal XM193 55 grain FMJ and shot them as fast as humanly possible through each rifle, then swiftly stripped them down to get pictures of the parts immediately after firing. I chose 4 magazines because it is about what most chest rigs carry and it is about the most consecutive magazines I have ever run back to back in a training class. The AK was shot with Wolf. When looking the parts over I found the following:



    SCAR IR Images









    Colt 6933...











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    Awesome info! For some reason, I also felt like weighing the SCAR today.

    Here's the rest of the weights for anyone interested:

    Upper Receiver Assembly 60.7 oz (Receiver, Barrel, Gas block, BUIS)
    Lower Receiver Assembly 14.6
    Folding Stock Assembly 19.3

    Bolt Carrier Assembly 20.5
    Return Spring 1.3
    Charging Handle 0.2

    Bolt Assembly 2.1
    Firing Pin 0.2
    Firing Pin Retainer 0.1
    Bolt Cam 0.2
    Bolt Carrier 11.9
    Last edited by Squid; 09-30-10 at 14:08.

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    Part 3

    AK.....





    LWRC...





    The Scar had a lower chamber temperature over the 6933 by about 30 degrees in this test. It is really hard to compare the AK to the other 3, I mainly ran it just for observation.

    I use to be an all out DI guy, and IMHO an AR should be a DI rifle. Although, one cannot ignore the benefits of having the moving parts of their weapon run cooler. Even at this point, discounting the benefits of keeping the carbon buildup common on the DI system out of the receiver, the lower temperatures of the Scar’s moving parts group chalk up another huge benefit of the Scar’s gas system and piston firearms in general. A common weak spot in a cylindrical piece of metal is at the change in contour or diameter. Having a large hole drilled through doesn’t help matter much either. I see rotating shafts break all the time at work for many different reasons, but what you will notice a lot of times, the break or failure point is at a change in diameter or contour. This is especially true with abrupt torsional loads applied to said part. The AR bolt has the most heat introduced to it at a significantly reduced diameter, right beside a hole drilled completely through it. This area also bears the force of being pushed forward briefly, then pulled violently rearward while a twisting motion is imparted upon it against the friction of the spent cartridge in the chamber. When this rifle is run hard time and time again, the parts heat up significantly in a short period of time and cool back down, over and over, throughout the course of, for those of us who use their rifles, many thousands of rounds. Full auto is even more severe. This heat up and cool down over time heat treats the part, and probably makes it more brittle over time. Most have seen the recent high speed videos showing bolt bounce on an AR on youtube.
    http://www.youtube.com/watch?v=575Q0...eature=related
    Now take your AR, pull the charging handle to the rear just a little, enough so that you can see the bolt. It is by this time you are able to see that the bolt is already starting to unlock and turn. So the amount of bolt bounce in some of those video clips not only affects the carrier, but the bolt twisting and moving axially as well to an extent. When you have this happen on every shot, every time the bolt carrier bounces it is even more undue wear on a heated, stressed part. When you step down from a rifle length gas system, to the carbine you step up in gas pressure to the carrier and the velocity that the carrier moves at increases. This also increases the rate at which parts wear. The M16 is rated at 700-950 RPM. As shown later on, with the heaviest Colt buffer installed in my Colt 6933, the ROF was still at the high end of what the M16 normally runs. So that is as good as it gets for the short guns with stock gas ports. When run with normal carbine buffers, and suppressors things get even worse for parts. The rifle was never designed for this use. It was adapted to it. Does it work? Yes, but is it optimal? IMHO, far from it. Most things done to make ARs in 14.5” or less configuration run are band aid solutions. The excess strain on parts that were designed for much less abuse causes tolerances to open up. The cam pin and the hole are constantly battered beyond that of which they were designed. Tolerances open up and eventually you start to have part failure. This is a reason, I feel, the Scar is a bit superior to the AR. It doesn’t matter what length barrel you have, the gas system is the same. The only variation lies at the gas port. (scar gas port pic) It can be set up to run the same with a 18” barrel as it does with a 10” barrel. There is no extra special extractor springs, action springs, trying/using different buffer weights, and different gas tubes, just a small insert in the gas block to vary the flow to the piston. Where bolt bounce is concerned, even if the carrier does bounce in the Scar, it has almost a half inch of rearward movement before it ever starts to impart a rearward, twisting motion on the bolt.

    While we’re on bolt bounce, after watching said high speed videos, something stuck out to me. One of the carriers consistently had a significant amount of bounce to it. This could be a bearing surface contact/tolerance issue, because if you look closely you will see the rear of the carrier moving up and down, along with back and forth. This gets me to another point I like about the Scar. I took my handy dandy calipers and measured/totaled up the bearing surfaces on the M16 BCG and came up with a total of 0.425” of contact between the bolt carrier and the upper receiver. From what I read on the Scar (and I could be wrong here), I got 1.181” of total bearing surface.
    AR..

    SCAR..



    Looking at the heat signatures and values of the Colt vs. Scar vs. LWRC, obviously the piston AR is cooler on the BCG than the DI. I have my doubts about the long term durability of some piston ARs and here is why. When the gas enters the BCG on a DI rifle, it enters an expansion chamber of sorts. The seal of the gas rings allow the gas to push rearward on the carrier and at the same time pushes forward on the bolt. To me, and I have no way of proving, this mitigates the amount of force applied to the rear of the bolt lugs and the front of the chamber lugs while the bolt unlocks. The piston ARs lack this. Theirs is a very violent smack rearward. I think that over time the piston ARs, whose bolt design is similar to the HK, might fair a little better than the ones that stuck with an AR style bolt. The shock on the cam pin area in the violent smack of the piston will probably be weathered better by the solid shape bolt of the HK. I think the Scar side steps this in some ways because of the more gradual unlocking of the bolt/turning of the cam pin. Not to mention the placement of the force applied to the BCG in the piston AR. The DI BCG is pushed by the gas from the center of the carrier. The piston AR BCG has an offset force applied to it, compared to the DI. I think if you are going to go piston, go with a different gun like the Scar that was designed with the piston action in mind.

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    Part 4

    Charging handles; at first I had reservations of the Scars reciprocating charging handle. For me it is has been a non-issue. I do have it from a very knowledgeable source that the charging handles have been an issue in some unconventional shooting positions. It can for some transitioning from the AR, be a little difficult to get use to. The muscle memory says to reach back a few more inches to work the charging handle. Maybe this is something that training will overcome? I have actually found I favor the Scar charging handle over the AR and here is why. I can visually glance down without canting the rifle and tell if I am out of ammo or had a malfunction. On the AR, you have less than a 1/16th of an inch “overlapping” contact from the charging handle to the carrier.



    With the Scar it completely penetrates the carrier and is significantly larger in size. I also find the position more natural for me, whereas the AR has always felt a little awkward pulling back that close to my body.

    One problem with AR15 rear sights with dual apertures is when flipping from the small diameter hole to the large, you will get some impact shift with your group down range. Dean Caputo did a great article on this in a past issue of SWAT magazine. The Scar rear sight aperture is mounted on a pin, instead of a screw. This should negate the impact shift when going from the large aperture to the small.



    The feedramp angles on both rifles are different as well. From my measurements, the Scar had a feedramp angle of about 39 degrees. The Colt 6933 with M4 feedramps had a feedramp angle of about 50 degrees. This should help in cartridge feeding.

    Getting back to the heat signatures; one thing you cannot really tell from the provided pictures, but having observed the rifles for a period of cool down time after firing them, the Scar definitely cooled faster. This was odd at first, as my 6933 has a small diameter barrel as well, but what it doesn’t have is a big honkin heat sink attached to it at the chamber. The lower rail did an amazing job of pulling the heat out of the barrel and helping it cool faster. I know a lot of folks say the railed handguards of the AR do this. They do offer better cooling than the standard plastic handguards, but not anywhere approaching how fast the Scar cooled with the lower rail attached to the barrel. I’m betting FN did their homework on this one.

    For what it is, the Scar seems to be a very accurate combat rifle. Mine has been exceptionally accurate. I believe there are a couple factors to this. One, in the readings I captured, the time it took for the hammer to impact the firing pin was about .001 to .002 seconds faster than the ARs I had on hand. Also, the Scar seemed to show fewer harmonics throughout the firing cycle than the ARs, especially the piston AR. I also believe the slower cyclic rate gives what harmonics the rifle has time to settle out before the next shot is fired. The overall bolt travel on the AR is close to 3.8” give or take. The Scar is, from my measurements, a little over 5”. To me, this is another plus for the Scar as it gives the magazine just a little bit more time to present a round for feeding. In the readings taken during firing, the Colt 6933 with the H3 buffer had a total firing cycle time of .064 seconds. The time from cartridge ignition through ejection and new round pickup was .020 seconds.

    The Scar had a total firing cycle time of .102 seconds. The time from cartridge ignition through ejection and new round pickup was .042 seconds.

    So the Scar gives the magazine twice as long to present a round for feeding than my 6933 does. Another plus! I know the argument could be made that the Colt has an 11.5” barrel, and the Scar has a 16” barrel, but if the gas system for the Scar 10” barrel is turned to have a cyclic rate identical to the 16”, this timing would not change.

    Rate of fire: I took several sets of readings on 3 consecutive shots to determine the rate of fire for the rifles tested. The way I have figured the ROF on these since they are not true full auto firearms is to take the time from the hammer dropping until the bolt closes on a new round. Granted this is probably not a true ROF as the few milliseconds that the auto sear tripping would take up are not figured into this, but that would not change the rates posted much at all. The period of time between shots was not figured into this as that time would obviously vary from shot to shot. What I found was interesting. The Scar was by far and away the slowest, and yet again I feel this is a big plus. Another thing to look at in these graphs is first large peak and the last large peak for each shot. The ones that exhibit a large spike as the shot is fired and less as the bolt closes will have a more substantial recoil impulse. If you look at the Scar, the firing and the bolt closing are very similar in levels. This shows the smooth recoil impulse of the Scar and what people describe as minimal muzzle rise and staying on target. I would say a higher level of G’s at the end of the firing cycle would be better for a smooth recoil impulse. The Noveske exhibits fairly low G levels overall, and a balanced recoil impulse. The LWRC has a very sharp beginning to the firing cycle, compared to the end. This does not lend well to a balanced recoil impulse. In looking at the Scar, the heavier mass of the bolt carrier is no doubt crucial to helping balance the recoil impulse out, as that mass slamming back home at the end of the firing cycle helps keep the muzzle down. The testing broke down like this:

    The average ROF of the Scar on the normal gas setting without a suppressor was 623 RPM. I think FN says 650. That is pretty close.


    The average ROF of the Scar on the suppressed setting without a suppressor attached was 533 RPM.


    The average ROF of the Scar on the normal gas setting with a AAC 762SD attached was 687 RPM.


    The average ROF of the Scar on the suppressed gas setting with an AAC 762SD attached was 591 RPM. One thing to note here is the overall level of G’s in this reading. The Scar with the suppressor attached is a very smooth firing rifle compared to the others.


    Colt 6933..
    The average ROF of the Colt 6933 with an H buffer was 1011 RPM.


    The average ROF of the Colt 6933 with an H2 buffer was 962 RPM.


    The average ROF of the Colt 6933 with an H3 buffer was 900 RPM. What is interesting, the increase in weight from buffer to buffer had about a 50-60 RPM decrease in ROF.

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    Part 5

    LWRC M6...
    The average ROF of the LWRC on setting A was 928 RPM.


    The average ROF of the LWRC on the normal setting was 947 RPM.


    The average ROF of the LWRC on the suppressed setting without a suppressor was 855 RPM.


    The average ROF of the LWRC on the suppressed setting with an AAC 762SD was 1018 RPM.


    The average ROF of the LWRC on the normal gas setting with the AAC 762SD was 1005 RPM.


    With the gas setting regulator on the LWRC, I expected to see a little more deviation on the cyclic rate. I was quite surprised that the cyclic rate with the suppressor and the gas setting on suppressed was higher than being fired suppressed on the normal setting. I do realize that I am an example of one with one rifle, and I imagine it might be different with other rifles, but it was none the less surprising to me. I also had a Noveske N4 Light 14.5” Switchblock on hand to fire. Of course the Noveske would not completely cycle on the suppressed setting, which makes calculating the suppressed setting ROF near impossible, but I did get the ROF of the normal setting.

    The Noveske had a ROF of 714 RPM.


    The Noveske also exhibited a very smooth, clean cycle of fire, more so than my 6933. I did not get the opportunity to fire the Noveske suppressed, but I will in the future along with a full length 20” AR, and a 16” midlength. I would love to do the same thing with Grant of G&R tactical’s suppressed only SBR. I would say, in looking at it from the perspective of the vibration readings the Switchblock is a step in the right direction for the DI system, especially if one intends to run a can. I would imagine the same could probably be said for what Grant is doing with the suppressed SBR designed to function with suppressed fire only. I had a conversation with Ken Elmore of SAW via email long ago where he expressed this same opinion, that for an AR to run in optimum condition suppressed it should be set up to function suppressed only.

    I also had a Norinco 7.62mm AK on hand. I found the average ROF of the Norinco to be 716 RPM.


    Parts availability/review. You read this online all the time, “lack of parts is a deal breaker for me…..”. This is how I see it. How long after the AR15 was introduced to the public market were barrels, bolts, extractors, action springs, buffers, BCGs, gas keys, FCGs…..easily and readily available? If you had an AR15 in the early 1960’s and it broke, what did you do to rectify the situation? Furthermore, how long after the 1911 was introduced to the public market were parts outside of Colt available for it? The Scar has only been around for a few years, even less in public hands. In those few years it has undergone very extensive proofing and testing, more so than the ubiquitous AR15 and 1911 combined during their inception. The first civilian Scar 16s sold when, around the 1st of January 2009? You can currently get some parts for the Scar. Anything else that breaks, FN will hopefully take care of it. I have talked to several folks who were shooters in the time around the introduction of the AR. From what I have been told, for the average Joe parts for the AR were non-existent for years after it was introduced for sale. The US Military is using the Scar FOW operationally. I can only imagine other countries will do the same in time. I, at this point, don’t feel this is a valid enough reason to drop a system that can be shown to be a better machine. As far as parts price, Colt has long been viewed as the gold standard in the AR world. Has anyone ever seen new Colt parts that are cheap? A Colt Bolt is around $160 from Colt sources. I realize you can buy other makes that are just as good for less, but that is really comparing apples to oranges to me. I don’t even consider the availability of parts not made to the TDP. Not with my money. Colt parts are high, and so will factory FN parts.

    The timing increase during the feeding cycle over the AR should help with some feeding issues common to the AR15. The timing of unlocking of the bolt is longer on the Scar, which should help in some common extraction/case head separation issues. The heavier mass of the carrier should help in some common AR feeding issues as well. The moving parts stay significantly cleaner and cooler, with no apparent degradation in accuracy common in some long stroke piston systems. The firing pin retaining pin issue should no longer be an issue. Hopefully the shape, size of the bolt and gradual twist of the cam pin slot will make the breaking of the bolt at the cam pin hole no longer an issue. The increase in extractor size and length cannot hurt. I think the polymer lower will probably hold up fine, as there is really not that much stress on that area of the rifle unless it is abused. Although there is a love/hate relationship for some of the charging handle, one cannot ignore that the bending, breaking, shearing of the AR charging handle will not be an issue with the Scar from using one hand to pull the charging handle to the rear. Not to mention the ability to lock the bolt to the rear without an aftermarket part or taking your firing hand off the grip. Most all of us who train or read the training AARs, know that taking your firing hand off the grip makes a certain short colorful Irishman from NY spew foul language, and probably kick puppies and babies in private at the end of the training day, not to mention what it can do to you in a bad situation. The lower rail does an extremely good job of pulling heat away from the chamber area of the Scar barrel, and even though the barrel heats up fast, it cools fast as well. I do not foresee the 5.56mm cartridge going anywhere anytime soon. If it does, the modularity of the Scar system could easily lend to adaptation of another round. Figure out a reliable magazine design for said new round and tool up the injection molding machines to make the lowers. I think the weight of the current crop of Piston ARs is also a drawback, especially the front end weight which leaves you with an unbalanced rifle. You still have charging handle issues, you still have the same length of bolt travel, cyclic rate is close to the same (which gets back into giving the round time enough from less than optimal magazines to present itself for feeding). You get too thin profile of a barrel on some piston guns and accuracy can suffer. The folding stock, while it may not be beneficial to some, can be a deal winner for others. Think about the space saved in an already cramped and overfilled patrol car front seat. If the proper cruiser rack were available, the Scar would be very easy to charge in route to a hot call. Technically, the way an AR has to be charged one handed while driving is the exact way that causes some charging handles to shear and break roll pins. Not to mention with the Scar sitting immediately to your right in a rack, you can glance down and visually reference that the bolt closed while in route. You would have to roll an AR inbound or feel it to tell this. Pop the magazine out and you have your loaded round indicator. For undercover work, a 10” AR would have to be broken down to fit in the same size bag as a folded Scar, then would not be readily available should trouble arise on the way into position like the Scar would.

    Things to Improve/Concerns:
    Lubrication: The manual states “to lightly lubricate all moving parts with CLP”. I realize this manual has to be written so the lowest common denominator of society can read and understand it, probably for liability purposes. I disagree with this procedure though. I know the military heavily uses CLP, and possibly that is why it is suggested, but anyone who is reading this knows there are far better lubricants available than CLP. The motion of the carrier through the upper is almost identical to a sliding glide linear bearing. Most of those types of assemblies I have seen in use in other fields are grease lubricated. This is true even in some very harsh operational environments. I would say a good oil like Slip 2000 EWL, Mobil 1…would be great on the bolt, cam pin, inside the bolt housing, but a good grease would probably be better suited for the actual bearing surfaces of the carrier. Not a lot of grease, just something to keep the metals from rubbing. The carrier is not subjected to heat like the AR15 carrier is, so a good grease should not turn runny and cook off. A benefit of the grease would be it will be more apt to stay put during use in rain or water. For very harsh environment use, I wonder how something like the dry lubricants and surface treatment agents from Molykote or other companies would do in this application. If they would hold up and work well over time, yea it might be another step/expense in manufacturing, but make the rifle a little more suited for harsh environment use.
    Sling attachment. I can’t help but wonder if they would not have been better off making the hinge part that attaches to the rifle and the stock latch out of aluminum. That would give some area to place the recessed sling QDs, similar looking to how the KAC SR15 E3 rifle looks. A QD should have been a no brainer as well.
    Rail space; maybe bringing the upper out and around the gas block, but not completely surrounding it so to still allow for barrel removal. Just enough to give a little extra room to accommodate different lights. Of course, over time lights will probably grow smaller and smaller, so it will probably become less of an issue.
    I noticed that the carrier impacts on just one side of the barrel extension. The carrier has a good bit of momentum when it goes home. I realize the chambering of the round softens this somewhat, but still I have to wonder if longer term issues may arise from the carrier making contact on just one side of the barrel extension. It may be a non-issue, and may be done for a reason; but it is just something that stuck out to me.
    I have read online, and I have no firsthand knowledge of this, that there have been some cases of stripping the threads out on the holes that secure the barrel to the receiver. If this is the case, would it not be a good idea to make the holes in the barrel assembly oversized and use helicoils in them? That way if one is stripped the helicoil can simply be replaced. Would the helicoil not be a viable fix for someone who does happen to strip out any of those holes?
    P-mags: One cannot ignore the P-mag is one of the most popular magazines out there. My Scar would not reliabily drop the P-mags I owned free. I have prior to buying the Scar, invested a good bit into a stock of P-mags. Lots of other folks have done the same. I really at this point see no reason to buy anymore aluminum magazines for my AR/Scar. I cannot understand, why the Scar 16s lower would even have an issue with the P-mags from the start. I know it goes back to the Mil probably spec’d out the GI mag, but how many P-mags are in use in the military now? It only makes sense to me to make them compatible. I measure the Colt magazine well and compared it to my Scar. I didn’t really have an issue on the side to side dimension, just the front and back. I got 2.3980” on the Colt and 2.3925” on the Scar. OK, almost .006”. Sounds like work for my sanding stick.

    Future Maintenance Issues/feedback/problem sharing. With a new weapon system, or any machine for that matter, will come unfound issues and trouble down the road. I am not going to sit here and pretend the Scar is perfect and will not have issues crop up as time goes on. I have seen way to many “perfect” products break in my job to subscribe to that. I do believe in this, all things man made can break; those that were designed and tested thoroughly, made well by craftsmen who care about the product they turn out, and assembled of the right quality materials for the task at hand will tend to break less. Just about all industry is the same in the following regard, but I have noticed the firearms industry is especially close looped in manufacturer to user communication. I will not name names, but there is no shortage of examples in Mil, LE, and Civilian circles of certain re-occurring problems cropping up in certain guns or accessories. The song almost always goes, “oh, it’s not a problem with our product, it is a user issue” or “our guns are the example of perfection, they don’t fail you must be mistaken, it was your fault, here use our weapon light instead”. Only to find out later on down the road, lots of folks were having that very same problem, and guess what that manufacturers perfect product, well it went through redesign to fix the problem they said wasn’t a problem to begin with. With a new system coming to bare, this would be a great opportunity to get out of this cycle. With the current crop of well informed gun forums online, if FN steps up and (without giving away trade secrets) uses these resources to communicate back and forth to consumers any found future issues, problems, benefits…, just think what a breathe of fresh air that would be. They have the opportunity to set the example here. A whole cottage industry of Americans have jobs, thousands of parts are made in the US because of the AR15. I think the Scar has the ability to be even more modular than the AR, and if supported over time could help get even more people to work here in the US. The bottom line of any company is to make money. FN will be making the parts for the Scar anyways, why not make sure there is enough for end users to completely support their rifle from the start. Doing so will eliminate the excuse given by many for not buying the Scar due to the parts issue. For a system based on modularity, give the end user the choice and ability to change and replace their barrels. Someone is going to eventually copy the receiver extension and make their own gas block, then sell their own barrels. Might as well be FN making the money, right? If the Scar does take a big hold in the Military, be it the Mk16, Mk17 or both, communicate the problems found through use and abuse to the users who spend their hard earned money on your product. Don’t do like some other companies have done in the past. The fate of the free world will not rest on whether the users on the civilian side of the house find out that down the road there is an upgrade to the extractor spring or barrel diameter and they don’t have it. In all seriousness, if it weren’t for the material passed on through the years of experience and hard work from folks like Dean Caputo, Pat Rogers, Larry Vickers, etc., what would we know about how to properly set up, maintain and shoot an AR15 or M4? The Pony Company isn’t readily giving that information out. An example would be weapon specific malfunctions. Certain weapons exhibit malfunctions that are unique to that weapon. Then there are weapons specific ways to clear those malfunctions. If there are any known, pass on the knowledge. Get the right information out from the beginning with a central reliable source of information, so that 20 years from now we can avoid the misinformation nightmare that we have with the M16/M4/AR. That way we don’t end up with some poor cop or soldier getting wounded or killed because he was instructed from so and so to “put a light coat or oil on the moving parts” when he should have been lubricating it significantly with a good quality oil.

    We know that the DI AR will run for a long time, even if cleaning is neglected, so long as it is lubricated sufficiently. Go shorter than the original design, and parts wear more frequently. It is the nature of the best, plan accordingly. I have several and do not plan on parting with them. I am not arguing that point. But a weapon like the Scar will on average run, with significantly less lubrication, less maintenance, and less down time than the DI rifle will. How is that not a plus? I am just looking at it from the standpoint of I have a task of, lets say shooting 10,000 rounds of ammunition accurately at a target over a given period of time using a weapon purchased with my own money. Why would I choose machine “A” my factory Colt 6933, a system that is exponentially dirtier, hotter, requires significantly more lubrication to account for the lubrication burnt off by the heat of the parts than machine “B”, my FN Scar. Machine “A” is more labor intensive to keep running properly (cleaning carbon crud from the heart of the system). Machine “A”, as comes from the factory in standard configuration does not handle the heat off barrel near as well as machine “B”, nor does it give me the option of mounting accessories to it. So I have to buy a free-floating rail system to help with cooling, accuracy, and mount stuff to, aftermarket part number one. Machine “A” comes from the factory with extractor spring “x” installed, but it is widely known that is not the best spring to make machine “A” run in optimal condition. So aftermarket part number two I have to buy. Machine “A” also does not come from the factory with the best buffer weight for that length barrel/gas system. Machine “B” does. So I have to buy an H2 or H3 Buffer for machine “A”, aftermarket part number three. Machine “A” is not ideally set up for the employment of optics and BUIS like machine “B”. So I have to scratch the carry handle and get an aftermarket BUIS. Pretty soon, to get machine “A” up to the capability of machine “B” I have spent close to the same amount of money. Granted there are DI systems that come setup right from the start, but the difference in cost really becomes less and less. In the end, it is the individual’s money and decision. Just make sure you make your decision based off your actual needs and facts. I for one am quite happy with what I have found with the Scar. I think as far as a machine goes, FN did a pretty good job with it. Thanks to my Father, Roger, Dean, Karl and a few others for their help in making this happen.

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    Very nice, thanks.

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    I would include the buffer weight in the BCG comparison.

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    Lots of info. Thanks for putting the time and effort into it.




    I do think there are some weak spots on the AR, and some of the newer guns like the SR15 address quite a few of them.


    Ive been around AR's for quite a few years now, and I haven't seen in person 3/4ths of the issues you pointed out. Sure they can happen, and do...but I think the concern is way overstated. Ive seen hundreds of military guns, and many privately owned guns in use that were all reliable weapons in vast environmental and temperature conditions.


    I also don't get the concern over lube burning off. With how many rounds it takes for lube to burn off, and start causing malfunctions you are talking about 4-5 + basic loads (210 rds is a basic load). If someone has to shoot that many rounds without being able to do a little maintenance on their gun they have much bigger issues to worry about. No one is going to be shooting thousands of rounds between being able to squirt some drops of oil in their gun unless they are doing it on purpose as some sort of "test" that has no real world application.


    As far as "shitting where it eats" type arguments Pat Roger's has done numerous long term endurance tests, and DI guns will keep running without being cleaned. I personally ran my SR15 to around 5k rounds without cleaning, and shooting cheap crap ammo. It still worked before I decided to just clean it.


    SBR's are not a good indication of the characteristics of the AR/M16, and yes there are better systems out there for running short barrels.


    I shoot a variety of AR's on a weekly basis, and I can't even remember the last time I had a failure to fire or any type of failure of any kind. But I started out with quality firearms and parts to begin with, and use good mags. I do maintenance on my guns.


    The SCAR/AR argument seems like a rehash of the AK/AR argument because say you can bury an AK in the mud for weeks, pull it out, and it will fire without issue. IMO the AR will be popular for many many years to come even with guns like the SCAR. The popularity is going to be limited to folks who have the money for a $2500 gun, and people who want one more than an AR.


    Parts may come for the SCAR, and maybe then it will become more popular.


    A lot of the bad rep AR's get is because the market is flooded with crap commercial guns, shitty mags, people shoot shitty ammo in them, don't do maintenance on them, home builds from crap parts by people who have no business with a tool in their hand let alone putting a firearm together, bad habits like soldiers keeping their guns dry because some dip shit told them to or it looks pretty for inspections, people not being able to identify bad magazines until it gives them issues, dumb asses in general, ect. If you took the SCAR, and had companies like DPMS, Rock River, Oly, Bushmaster, ect making the do you think it would still be a quality weapon with their cost cutting, poor QC, ect?


    I also hear people comment about how little recoil the gun has, and how smooth it shoots. They come from the factory with a comp already installed. You can do the same thing with an AR. My SR15 with the Triple Tap barely has any recoil. Its like someone tapping you on the shoulder to get your attention type of soft, and there's very little muzzle rise.


    While the heat dissipation may be better on the SCAR what effect does that have in real life, and does that mean the hand guard gets so hot you need gloves to handle it?


    In my way of thinking the only thing that really matters is if the gun shoots when you need it to, and can you hit the target with it? Does it do its job in the way it was designed to? Why are failures occurring. Is it a design flaw? Poorly made part? Operator error? Using the gun beyond what it was designed to or out of its role? Was maintenance done on it?


    Im not knocking the SCAR as I do think its a pretty good gun just based on everything Ive seen. I very may well buy one down the road as I would love one with a factory SBR barrel and a can. I just think DI AR's get a bad rap for the wrong reasons or reasons that are not really realistic. You are also comparing an AR of a very old design, build, and assembly method because the military has not changed with the times. You should compare something like an SR15 which is the very latest in AR design, and has addressed most of the issues you mentioned. The bolt is warrantied to 20k rounds which is unheard of in the AR world, and real world testing has shown it can go much further beyond that. Ive owned and shot lots of different AR's, and without a doubt it is the best there is for what it was designed to do. I have not had a single malfunction with it in the last 10k rounds, and it has a hair over 14k now. Ive owned it for less than a year so its somewhere around 1500 rds a month on average.


    Just an example of issues that have given AR's a bad name is 2 stage triggers, and Ive had to go to great lengths to convince people that the newer combat oriented designs like the SSA really are a good reliable trigger. The AR market has been flooded with crap parts that have given things like 2 stage triggers a bad name. The AR has been around so long, and so many companies make them you constantly hear of people having issues. I wonder how the guns I have can run so well, and I "almost" never have an issue. But its because people don't want to spend the money for good gear, and then end up buying something like a DPMS. Its very rare to hear of issues with the top brands, and especially so from people who know how to run them. Just look at all the carbines out there with 16" barrels, and its been well known that barrel length on the AR is not a good combo yet its the "standard" AR seen in shops across the country. Its only a recent phenomenon to see 14.5" mid lengths being used with some regularity, and is proving to be a much more ideal gas length for barrels of 14.5" and 16" lengths.


    Thats just my take on it, and again thanks for putting all that together.

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    Quote Originally Posted by Belmont31R View Post
    Lots of info. Thanks for putting the time and effort into it.




    I do think there are some weak spots on the AR, and some of the newer guns like the SR15 address quite a few of them.


    Ive been around AR's for quite a few years now, and I haven't seen in person 3/4ths of the issues you pointed out. Sure they can happen, and do...but I think the concern is way overstated. Ive seen hundreds of military guns, and many privately owned guns in use that were all reliable weapons in vast environmental and temperature conditions.

    Just in taking my 6933 apart and cleaning it up for the pictures, I found a crack in my Colt bolt at the cam pin hole. It happens quite a bit. Maybe not the cam pin break on Colt bolts, but failures are common. It is common enough that the DOD has a presentation on it, shown in Dean Caputo's class.


    I also don't get the concern over lube burning off. With how many rounds it takes for lube to burn off, and start causing malfunctions you are talking about 4-5 + basic loads (210 rds is a basic load). If someone has to shoot that many rounds without being able to do a little maintenance on their gun they have much bigger issues to worry about. No one is going to be shooting thousands of rounds between being able to squirt some drops of oil in their gun unless they are doing it on purpose as some sort of "test" that has no real world application.

    Maybe it isn't so much about not being able to, but having the luxury of not having to do it so often?[/I]


    As far as "shitting where it eats" type arguments Pat Roger's has done numerous long term endurance tests, and DI guns will keep running without being cleaned. I personally ran my SR15 to around 5k rounds without cleaning, and shooting cheap crap ammo. It still worked before I decided to just clean it.
    I agree, and stated that whe properly maintained a DI gun will run quite well; I have done the same kinds of shooting with my DI guns as well.[/I]


    SBR's are not a good indication of the characteristics of the AR/M16, and yes there are better systems out there for running short barrels.

    [I]Maybe not for everyone, but for me, the majority of my ARs are SBRs, so it is very applicable



    I shoot a variety of AR's on a weekly basis, and I can't even remember the last time I had a failure to fire or any type of failure of any kind. But I started out with quality firearms and parts to begin with, and use good mags. I do maintenance on my guns.

    [I]As do I



    The SCAR/AR argument seems like a rehash of the AK/AR argument because say you can bury an AK in the mud for weeks, pull it out, and it will fire without issue. IMO the AR will be popular for many many years to come even with guns like the SCAR. The popularity is going to be limited to folks who have the money for a $2500 gun, and people who want one more than an AR.

    How many high quality ARs are $2200 guns (what I paid for my SCAR)? There are machines that are fundamentally/inherently more reliable than others.

    Parts may come for the SCAR, and maybe then it will become more popular.


    A lot of the bad rep AR's get is because the market is flooded with crap commercial guns, shitty mags, people shoot shitty ammo in them, don't do maintenance on them, home builds from crap parts by people who have no business with a tool in their hand let alone putting a firearm together, bad habits like soldiers keeping their guns dry because some dip shit told them to or it looks pretty for inspections, people not being able to identify bad magazines until it gives them issues, dumb asses in general, ect. If you took the SCAR, and had companies like DPMS, Rock River, Oly, Bushmaster, ect making the do you think it would still be a quality weapon with their cost cutting, poor QC, ect?

    [I]This is why I only buy quality guns/parts.[/I]


    I also hear people comment about how little recoil the gun has, and how smooth it shoots. They come from the factory with a comp already installed. You can do the same thing with an AR. My SR15 with the Triple Tap barely has any recoil. Its like someone tapping you on the shoulder to get your attention type of soft, and there's very little muzzle rise.

    The factory comp was not on my rifle at the time of the test. I was using the AAC Blackout. You can look at the level of G's in the data and see that it did infact off the shoulder have a softer recoil impulse than the ARs tested

    While the heat dissipation may be better on the SCAR what effect does that have in real life, and does that mean the hand guard gets so hot you need gloves to handle it?

    [I]More will be coming on this in the next couple weeks[/I]


    In my way of thinking the only thing that really matters is if the gun shoots when you need it to, and can you hit the target with it? Does it do its job in the way it was designed to? Why are failures occurring. Is it a design flaw? Poorly made part? Operator error? Using the gun beyond what it was designed to or out of its role? Was maintenance done on it?

    [I]I believe with the AR it is decades old technology being pressed into roles of which it never was intended. It does a good job, but are you saying that a better mouse trap cannot exist?[/I]

    Im not knocking the SCAR as I do think its a pretty good gun just based on everything Ive seen. I very may well buy one down the road as I would love one with a factory SBR barrel and a can. I just think DI AR's get a bad rap for the wrong reasons or reasons that are not really realistic. You are also comparing an AR of a very old design, build, and assembly method because the military has not changed with the times. You should compare something like an SR15 which is the very latest in AR design, and has addressed most of the issues you mentioned. The bolt is warrantied to 20k rounds which is unheard of in the AR world, and real world testing has shown it can go much further beyond that. Ive owned and shot lots of different AR's, and without a doubt it is the best there is for what it was designed to do. I have not had a single malfunction with it in the last 10k rounds, and it has a hair over 14k now. Ive owned it for less than a year so its somewhere around 1500 rds a month on average.

    [I]In comparing to the SR15, the timing of the firing cycle will not change by much, due to the length in the cam pin slot and bolt travel being near the same as a colt. The Scar still has the advantage, as shown in the data, of giving the round a longer period of time to present itself for pickup.[/I]
    Just an example of issues that have given AR's a bad name is 2 stage triggers, and Ive had to go to great lengths to convince people that the newer combat oriented designs like the SSA really are a good reliable trigger. The AR market has been flooded with crap parts that have given things like 2 stage triggers a bad name. The AR has been around so long, and so many companies make them you constantly hear of people having issues. I wonder how the guns I have can run so well, and I "almost" never have an issue. But its because people don't want to spend the money for good gear, and then end up buying something like a DPMS. Its very rare to hear of issues with the top brands, and especially so from people who know how to run them. Just look at all the carbines out there with 16" barrels, and its been well known that barrel length on the AR is not a good combo yet its the "standard" AR seen in shops across the country. Its only a recent phenomenon to see 14.5" mid lengths being used with some regularity, and is proving to be a much more ideal gas length for barrels of 14.5" and 16" lengths.

    [I]Agree, I'm not saying the SCAR is gods gift to man kind and the AR is a POS, I'm just saying there are mechanical improvements the SCAR has over the AR. Time will show if I am correct.[/I]


    Thats just my take on it, and again thanks for putting all that together.
    I appreciate it, a lot of work went into it and I plan on doing the same with the Scar 17 and the KAC offerings later this fall. If I can locate someone locally with the SR15 E3, I'll do it as well.

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    Quote Originally Posted by Todd.K View Post
    I would include the buffer weight in the BCG comparison.
    Will add that.

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    superb & extraordinary data thanks.

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    Amazing write up. Thanks for all of the fact based data. This proves a lot.
    Im glad to see someone working outside of the gun industry do the research that you have.
    Im a Maint Supervisor in a chemical plant and can appreciate all of the work that you put into this testing. Well done.

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    Outatanding work!

    Thank you.

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    great technical post and insightful observations. thanks for taking the time to compose it.

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    How many rounds through that 6933? The ROF seems quite high.

    The LWRC ROF unsuppressed is almost identical to the 14.5" HK416 data I have.

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    Looks like good information. Thank you for the effort.

    I too like the DI AR and the SCAR.

    I also believe the AR is best left DI and if a person wants a piston they are better off getting out of the AR altogether.

    I was surprised at the difference in temps. I did some testing and my numbers were closer. To explain though, I didn't run as many rounds and I used a cheap tool that is made for RC cars to get my temps.



    You briefly touch on the charging handle causing problems. I have posted this before, but I'll add it to the discussion here.

    With the charging handle on the left a person could run into trouble while shooting with the firearm in an abnormal position like the hood of a vehicle or when shooting under a vehicle (basically when the firearm is laying on the left hand side). In that sort of position I prefer the ejection port up and believe that under certain circumstances (having the charging handle on the left) the charging handle could cause a malfunction if it were to contact the ground, hood, rocks, pack, etc….

    I’m right handed, but run the charging handle on the right. The charging handle on the right corrects many issues for me including the issue I listed above.

    Benefits of running the charging handle on the right side (in my opinion)

    - Release bolt from both sides of the firearm
    - Clear field of view (doesn’t obstruct left eye)
    - Not against me when transitioned to pistol or movement
    - No issue with the Aimpoint and LaRue mount
    - Simple / Quick malfunction clearance during drills
    - Easy to spot a malfunction due to the position of the charging handle
    - Charging handle in the same place as on my shotgun and my semi-auto 308

    I know many folks prefer a non-reciprocating charging handle, but I like this set up.
    Joshua 24:14-15


    "The only thing necessary for the triumph of evil is for good men to do nothing" Edmund Burke

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    Well done.

    IMHO, I believe the SCAR is a superior platform over the AR (including the charging handle! ).

    BTW op, be prepared to be tarred and feathered by the AR fanboys.
    All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident. — Arthur Schopenhauer

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    Thank you so much for sharing these infos

    Thank you so much for sharing these infos ,

    PP out

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    Interesting read. Looks like you definately put some effort into the writeup. Thanks for sharing.

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