View Full Version : piston design evaluation...need help picking my first ar.
So right now I am currently in the market of buying an ar15 piston type rifle. After my research I have narrowed down my search to the LMT MRP and the PWS mk116.
From what I see the LMT is a short stroke design just like the lwrci rifle. And the PWS system is more like the ak47 system.
Can anyone chime in and help me decide which one would be a better rifle?
This is a very flammable subject, but... if it's your first AR, is there a reason you want to go with a piston? I'm not saying it's a bad choice, I'm just curious about your reasons.
JR TACTICAL
01-13-11, 23:59
Just to let you know you can use the search and find out alot about piston style AR's in here, just FYI they are looked down on from what I have read on this forum and alot of people will tell you a properly made DI gun from DD, BCM, or Colt will serve you just as good if not better than high dollar piston from LMT or LWRCi. I my self have owned bolth and I tend to lean toward the quality DI systems that are on the market because of what I have learned from this forum and now having owned bolth. Just do you research on here and go shoot bolth of them before you buy one and if piston is still the way you want to go I dont think you would be making a bad choice with either... me personally, I would go with LMT
just some food for thought
JR
Thanks for the warnings Guys.
For my reasons. I think its better to move the heat and debris away from the BCG. Sure its never going to be a true free float system but I wont be that accurate for it to make a difference. And honestly being easer to clean is a big plus.
pros and cons
pros
lmt: the upper rail is awesome. "free float hand guard", ability to change calibers quickly. The company has been around for a very long time.
PWS: long stroke piston system, only weighs 6lbs and 17oz (thats almost as light as the ddm4!), the design of the piston attached to the bcg looks like it will prevent tilt!
cons
LMT:dont know what one weighs, short stroke piston system.
PWS:dont know if they will be around in the feature, non free float hand guard, worried about mounting iron sights to top of rail(i dont want to re-zero sights every time i take off the top rail).
PS. i have done searches on sites and noticed there are not meny reviews of the pws system on the net. the only one i found was on snipershide and thats still an ongoing review with weekly updates.
Pistons are generally bad mkay, we need a sticky on em, etc., etc.
If you must run a piston AR, keep an eye out for tilt. IF you notice excessive wear on the buffer tube, I'd highly recommend that you install a Firearm Ready Solutions anti-cant buffer and spring set:
http://firearmreadysolutions.com/About.php
The heaviest you can run reliably, preferably. There are several other products on the market that will counter act non-linear forces on the carrier, but this has proven itself to be the most effective and simple solution. While carrier tilt is likely only a cosmetic issue, the possibility of a stress fracture in unchamfered carriers or carriers without "skiis" is too much of a risk for me. Another benefit to the FRS buffers is that you know the exact weight of your buffer, if your original manufacturer did not disclose this information, and you can be fairly certain that with an H3 buffer, for example, you'll be slowing down unlocking times and extending the life of your poor, poor locking lugs.
But you shouldnt need to know any of this anyways. You should just buy a DI gun. Just sayin.
Failure2Stop
01-14-11, 01:36
Being a long stroke or a short stroke is neither an advantage or disadvantage. There are good and bad examples of both.
Precision requirements of a working AR will not suffer by going to a piston. Molon did a great review of a retrofitted piston system, and compared precision before and after adding the modified operating system. Summary of precision loss: not much.
LMT makes a highly regarded piston operated cabine. Many people assume that it was a natural progression of the system due to failures identified by the manufacturer. Acutally, when asked why he designed and built a piston AR, Mr Lewis replied, "customer demand".
What it boils down to is that lots of people jump on the piston bandwagon before pushing their DI gun to their breaking point. If you don't shoot at least 5,000 rounds between cleaning, suppressed and unsuppressed, with a 10.5 inch barrel, there isn't anything a piston is going to do that a properly built DI gun can't do with a smoother recoil impulse.
If you really want to take advantage of a piston system, get one designed from the ground up to be operated as such.
Then again, if you just want a piston AR, go ahead and get one, it ain't gonna hurt my feelings.
ICANHITHIMMAN
01-14-11, 16:39
Get the MRP from LMT and you can have both systems. I got one after going through a bunch of other rifles first. I still have a DI gun but the MRP offers me a lot of other options.
I'd say if you can afford it and are set on a piston, get the MRP. That way, you can have a DI barrel/BCG also. My first AR was the LMT Piston only because it was in stock at normal price during the Nov '08 craziness (for like an hour)...I already have a DI barrel for it as well and have built a 2nd high quality DI AR (DD upper, LMT BCG) for half the cost. I haven't had any issues with the piston though.
I don't think there is any advantage for a non SBR'd, non suppressed weapon that the piston "advantages" has any tangible effect on increasing reliability. In many cases I think it decreases it. If you want something different for your own reasons or because you think that a cooler chamber increases the life of the system, then get one. Someday there will be one that has proven itself better than the others. When this happens, if it also proves to be a 40,000 round firearm, maybe, I'll buy one. Until then it's money better spent on aimpoints, ammo, or training.
Well before opening this thread I already knew what type of I hate piston's responses were gonna be in here. He asked between the LMT and PWS which should he get. He says he's done his research and that's where he's at. I understand giving advice but the piston threads always turn into this. So answer what he's asking, if he wanted a DI then he'd be asking about them. He probably knows the differences and has his reasons for wanting a piston.
Anyways, I'm gonna ask what caliber and size gun your looking at?
I'de pick an LWRC then LMT then PWS.
Well before opening this thread I already knew what type of I hate piston's responses were gonna be in here. He asked between the LMT and PWS which should he get. He says he's done his research and that's where he's at. I understand giving advice but the piston threads always turn into this. So answer what he's asking, if he wanted a DI then he'd be asking about them. He probably knows the differences and has his reasons for wanting a piston.
Anyways, I'm gonna ask what caliber and size gun your looking at?
I'de pick an LWRC then LMT then PWS.
Well aren't you doing what you just chastised us for doing............
No? I still gave him my choice between the two. Lmt over Pws.
Honestly, if you want a piston system that accepts M16 magazines, I'd look at a SCAR-L.
If you've got to have an AR system, then get the LMT, it will at least allow you to go back to a DI system.
Scar's rails get way too hot to touch.
This is the wrong forum to ask what piston to get, there are a few other forum's that have specific ar piston sections where you will get the info you want. Again there's plenty of data on the net to back up LMT piston's system and their function, reliabilty etc. Pws still needs to proove themselves to me, but they look like they might have something.
And the only reason I mentioned LWRC is because i happen to own one with over 10k rounds through it, and have seen plenty of info to back up their reliablity etc. Plus they have 2nd to none customer service.
variablebinary
01-16-11, 02:45
So right now I am currently in the market of buying an ar15 piston type rifle. After my research I have narrowed down my search to the LMT MRP and the PWS mk116.
From what I see the LMT is a short stroke design just like the lwrci rifle. And the PWS system is more like the ak47 system.
Can anyone chime in and help me decide which one would be a better rifle?
I've not fired the PWS, but I have shot/owned the LMT MRP piston, LWRC and the Robarm XCR all side by side.
The LMT and LWRC are both short stroke, while the Robarm XCR is long stroke. The LMT was the most picky about crap ammo, while the LWRC was the most accurate, and XCR was the most reliable no matter what garbage ammo I fed it.
I will say that the long stroke design feels vastly better to shoot, it has a nice smooth build up, lets off easily with all the recoil feeling consistent and easy. Short stroke is far more violent, with a sharp sudden impulse over a short distance and duration.
Again, I can't speak on the PWS, so I have no idea how it feels to shoot, how accurate it is or how reliable it is.
FWIW, I would take the LMT over the PWS or LWRC just for the MRP platform which brings XCR/SCAR/ACR features to the AR15, and allows you to go from piston or DI in a a couple of minutes for a fraction of the cost of a dedicated DI and piston upper.
Most people can't speak to which is better, because most don't own both, nor have they fired 10's of thousands of rounds to determine it. That's the basic issue: a Piston vs. Piston show down hasn't happened. If somebody knows something about it, they haven't posted it where any AR fans ever found it.
I think its better to move the heat and debris away from the BCG.
That statement is the main sales pitch of piston marketing, and it's usually presented as if it's bad to port gas into the carrier. What they fail to mention is that DI is Piston! When gas is ported into the carrier, it's trapped there by the back of the bolt, which has (drumroll, please!) gas rings. Yep, it's a piston - a stationary piston at that point. The system is designed to make the CYLINDER move, and that's the carrier.
Which is cleaner and cooler? Look at the thermographic studies, a AR BCG is only about 45 degrees hotter than piston, but the cylinder mounted on the barrel is hundreds of degrees hotter, as already pointed out. Most piston owners don't want to constantly clean their piston cylinders, most experienced DI gunners don't either. It's not necessary, plenty of guns are going thousands of rounds with just lube.
The entire point of the piston gun - to run cleaner and cooler - isn't happening. They run hotter, and then the operator leaves them dirty. The bolt gets dirty anyway from gas residue expelled around the brass as the chamber is opened. All self loading actions do that.
It's not piston hating to point out the marketing of them confuses the situation and deliberately compares apples to oranges. Break it down to it's components, a piston gun runs hotter, and gets just as dirty. For the $$$$ "upgrade," all I see is a kit to mount a piston on the barrel just to disable the piston in the bolt. Net gain is negative.
Direct Impingement is piston, look again, then decide.
thank you guys.
i have decided to go with the lmt due to versatility, and known quality of the rifles. I plan on getting a DI rifle and the piston kit. This way I can see what I like the best.
fyi: i also plan on getting the spikes 22lr barrel with the 22lr bcg for the times when i cannot get to the outdoor range.
With the pws system you dont get options...well you do sort of, you have .308 or .223, then choice of 12" or 16" barrels. But i like the having lots of options to configure the rifle.
Aside from the technical merits of the systems (which I much prefer LMT's offering) I wouldn't wager on the other companies being around in 10yrs.
Tirod and Dano5326 summed it up well. It would be wise to research DI and piston more, especially before buying a first AR. Don't fall in love with the hype before understanding both arguments.
And for anyone choosing piston, definitely buy spare parts now while your proprietary design is still offered and parts are available. Otherwise, your spare part will have to be a DI upper. Or someone else's piston upper.
Magic_Salad0892
01-18-11, 00:23
Wasn't one of the cool parts of a DI upper the fact that it eliminates the need for an op-rod assembly?
The DI upper is an amazingly simple (and more user configurable) system...
At the risk of beating a dead horse... :o
It's worth reading up on the realities of piston AR's from some of our resident experts.
From the man in the yellow visor:
Why Not a Piston AR? (https://docs.google.com/View?id=drnhb8z_242g54n2jfd)
And sequestered in the New to Firearms/Shooting sub forum that folks tend to blow by is this little gem from Robb on pistons:
Full Article Here (http://m4carbine.net/showthread.php?t=24397)
"If you are planning to build or buy a SBR or full auto or use a sound suppressor, I would suggest considering a piston gun.
Many people think they need a piston AR or they need to convert their standard AR to piston. Many of these people use the excuse that piston ARs run better than direct impingement ARs or run cleaner. This is not the case. Piston guns have their own sets of known problems. These are just different problems and weakness areas vs. standard direct impingement ARs.
Piston guns get dirty as well just not at the bolt, bolt carrier and in the upper receiver, piston ARs are more forgiving of the lack of lubrication (because the bolt and carrier aren't getting as hot and hot gas isn't blown into the action), they can be run with a little less lubrication than direct impingement ARs. I have the Primary Weapons carbine length piston conversion on my Colt 6920 upper. It gets plenty dirty. After a thousand rounds or so it looks like I've airbrushed carbon all over the gas block and the rail and barrel near the gas block. This is where it bleeds off the excess gas not used to cycle the bolt. If shooting without a glove on my left hand it gets very hot in this area pretty quickly, actually hotter than comparable direct impingement ARs.
Many piston ARs suffer from bolt tilt. Bolt tilt is where the carrier bottom side at the rear of it is slammed downward as it cycles, as the carrier tilts downward the first thing the carrier impacts is the bottom of the receiver extension and this causes gouging the receiver extension near the buffer retainer. These gouges can get so bad that the rifle will have some very unusual hard to diagnose stoppages which include short stroking, failures to feed etc. I have a friend who has over 20K rounds through his piston gun and it looked like someone took a rat tail file to his receiver extension. He's also now running an experimental anti-tilt buffer as am I. I'm using this experimental buffer which addresses these tilt problems, and it is working very well at stopping bolt tilt 100% so far. The Primary Weapons conversion does have least amount of tilt for conversion units, mine wasn't bad even before using the anti-tilt buffer but the carrier did remove a little of the finish from the inside of the bottom of the receiver extension. After getting the new anti-tilt buffer I started fresh with a brand new LMT receiver extension to track any changes .
Standard direct impingement ARs don't have bolt tilt issues because the gas chamber is in the center of the carrier and when the gas is expanded in that chamber this expansion forces the bolt carrier rearward and the bolt forward until the carrier moves far enough rearward that the bolt unlocks and follower the carrier rearward.
Piston ARs have bolt tilt because they have a solid mass (not gas) impact the top front of the carrier, or they have carrier key which is impacted by the op rod which is mounted high on top the bolt carrier. The natural first movement of the carrier is to cam down slightly before starting rearward. If not addressed this is why there is gouging at the receiver extension near the buffer retainer. Some companies address this with pads at the tail end of the carrier to limit the amount of tilt.
I run my piston AR almost as wet as my standard direct impingement ARs. If you are using a sound suppressor your bolt will run cooler, but it'll still be pretty dirty along with the chamber and barrel. So “easier to clean” is a very poor excuse for wanting a piston AR. The rail, inner sides of the rail covers and portion of the barrel around the gas block on my piston AR looks as if someone airbrushed carbon all over it. So it still gets dirty, it's just in a different spot vs. a direct impingement AR. I believe if one is too lazy to clean and properly lube an AR then one should just shoot an 7.62x39mm AK. This isn't a dig at AK owners because I am one. I currently have 3 and like them a lot. AKs can be shot for a long time with very little cleaning and very little lubrication. Many of the people who think a piston AR is as reliable as an AK also believe that 5.56mm is a poor caliber for defensive use. As a whole, piston ARs aren't anywhere near as reliable as an AK as many people believe. Some are very reliable, the HK416 is one example. Piston ARs vary quite a bit from one brand to another and they aren't created equal. There is no standard for piston ARs."
No matter which gas system you choose, getting a quality weapon is what matters the most. The DI vs piston thing is a never ending discussion. Personally, I believe that each platform has its merits and each has it's drawbacks. That's pretty much the same as with any weapons platform. Whatever the platform, buy quality and choose what works best for you.
OP, LMT is a great choice. Post some pics when you get your weapon.
as far as piston uppers, has anyone investigated the Rock River Arms piston upper/ complete gun?
I believe it's called the PDS (piston driven system)
Hard to beat LMT...the quick change barrel/gas system/caliber feature is an added bonus should you ever want to make a/some change/s.
Littlelebowski
01-22-11, 10:37
For my reasons. I think its better to move the heat and debris away from the BCG. Sure its never going to be a true free float system but I wont be that accurate for it to make a difference. And honestly being easer to clean is a big plus.
What experience are you basing this off of? Are you more concerned with cleaning than taking your savings and getting training?
It is very discouraging when folks are more concerned with cleaning than function and training.
RogerinTPA
01-22-11, 17:01
Well before opening this thread I already knew what type of I hate piston's responses were gonna be in here. He asked between the LMT and PWS which should he get. He says he's done his research and that's where he's at. I understand giving advice but the piston threads always turn into this. So answer what he's asking, if he wanted a DI then he'd be asking about them. He probably knows the differences and has his reasons for wanting a piston.
Anyways, I'm gonna ask what caliber and size gun your looking at?
I'de pick an LWRC then LMT then PWS.
I doubt it. If he would have done thorough research, especially on this board, and compared the two, he would not be asking for a piston gun. His other comment about pistons being easier to clean, is a typical uninformed novice comment, who has in fact, done very little research between DI vs Piston.
Well in my guns, my piston guns are cleaner after shooting. Easier is not the right word, they both come apart the same etc. It rarely takes me less time cleaning either because I'm just as thorough when cleaning either type. But if your basing your buying off of that factor then your buying for the wrong reasons.
It is very discouraging when folks are more concerned with cleaning than function and training.
Great dialectic verbal jiujitsu maneuver! I wish I would have thought up this response when this dude was trying to convince me why his LWRC op rod gun was better than my 6920 :D
I'm not much of a fastidious cleaner anyway, and over cleaning can be detrimental, but I'd rather clean a tad more and forgo the increased number of non-proprietary parts, weight, increased recoil impulse, carrier tilt, etc.
I have an idea. I am going to lock this thread. When the OP has finished doing some research and considered all of the pluses and minuses then we'll revisit this again.
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