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”.