View Full Version : One man's piston gun experience
I figured this was the right place to put this, but if not, sorry.
I thought I'd write this up as a potential data point for those that may have been seeking similar information that I was when I first started thinking about a piston gun. I offer this not as an argument, just what I've found with my use. I don't pray at the piston gun altar and the rest of my ARs are DI, so this is just my experience with one particular piston gun.
When I first started looking at building/buying a SBR, I was also looking at a piston setup. When I would start asking questions or when I'd read threads where other people ask questions, it would quickly turn into an unproductive argument that didn't really answer the questions asks. So goes the internet, I guess. A primary reason for my interest in a piston gun was to gain experience with one personally and make my own decision based off my own uses.
Briefly, here's what I built:
Mega monolithic upper (carbine)
BCM 11.5" barrel
Mega (Adams Arms) carbine piston system
and the normal other stuff (Troy, Aimpoint PRO, BC 2.0, lower, Gunfighter CH, etc)
Pic below, if it matters.
The gun has about 700 rounds through it now and I've had it for a year. Unfortunately I don't get to shoot it that often now due to PCS'ing to a NFA unfriendly state. I don't need the weapon to fight Jihadists and I don't need the weapon for LE. It's for personal, happy-fun times shooting. Also, it has not been through a carbine course and I haven't been able to compete with it yet (hoping to fix that in June). Until I've done at least one of those, I wouldn't say it's fully been broken in. Functionally so far though, it's been problem free.
So this leads me to the concerns/arguments about piston guns and whether I found them to be a problem for me. Here's some thoughts:
Weight: "A piston gun is heavier than a DI gun."
Heavier than what? Compared to my Noveske LW with a low profile gas block, it's absolutely heavier. Compared to a regular F-marked FSP...eh. I never bothered to weigh the gas block, but holding a standard front sight base and the Adams Arms gas block in each hand, they feel pretty close. I wouldn't be surprised if the piston one was a little heavier, but minimally so. It is certainly heavier than a low-pro set up. For me and this particular gun, I've found the combo of the barrel profile and the piston gas block makes it a little heavier than I would like.
Accuracy: "A piston gun is less accurate."
Possibly. I understand the mechanics say this is true. I also was next to a DoS contractor/Marine Sniper in a Magpul SPR/DMR class that was shooting a piston SPR (LWRC) and he was plenty accurate. As usual, it may often come down to the shooter more than the gun. For me, as a SBR and shooting M193 or M855 at 100 yards or less, it's plenty accurate (2-3 MOA with just planting my elbows on a surface). Plus I hate shooting for groups.
Sanitation: "A piston gun doesn't really run cleaner than a DI gun, especially with a suppressor."
My personal opinion is that some people like to parrot this that want to make a case against a piston gun but leave out the suppressor part. I haven't shot mine with a suppressor. I hope to eventually, but for now, I can only speak to shooting unsuppressed. The BCG is most definitely cleaner after a few hundred rounds. A quick wipe of the bolt lugs and face and a little oil and clean up is done there. But if you choose to clean the barrel after every time you shoot, results start to mirror a DI gun (which makes sense). That may or may not matter to some. Also, the gas block does start to accumulate carbon, but I find it to be much less hassle than what I find inside the receiver of a DI gun (just a quick wipe down with M Pro 7 and the GB is done).
Recoil: "It feels weird/different/etc."
I think it does feel a little different to me, but I'm not completely sure it's the piston (it might be). I was going to play with a heavier buffer the next time I shoot it. I feel a push, but I'm not sure if that's the impulse of the bolt carrier, the impulse of the piston or if it's just a rifle that's got a shorter barrel with a gas length I haven't shot as much (carbine vs mid or intermediate). It's not bad or distracting, just feels a little different to me.
So, lots of words, but is it the second coming of the AR or a train wreck? This was the first AR that I built completely from parts (instead of buying an assembled upper), so I was excited (and a little proud) that it worked from the first round. As for my overall reaction:
It's okay. I personally find the rifle a little nose heavy, but as I said, I think the barrel profile has a lot to do with that. When first shopping, I noticed the LWRC 10.5" uppers were the same way, but they also have a heavy profile barrel. Otherwise, it's been (so far) a reliable, low maintenance weapon that has done exactly what I've asked of it.
This got a little long, so sorry about that, but maybe it will help someone else thinking about whether to go piston or not. Or maybe it's worth what they're paying for it.
I'm not sure I get it, it seems kind of wishy washy....are you advocating your weapon/system or just showing it off to us? Its a nice gun but what are you getting at......??
I prefer the threads where guys come and spout the " second coming stuff" so the mods can teabag them to my delight.
I'm not sure I get it, it seems kind of wishy washy....are you advocating your weapon/system or just showing it off to us? Its a nice gun but what are you getting at......??
I prefer the threads where guys come and spout the " second coming stuff" so the mods can teabag them to my delight.
Please explain by it being "wishy washy"
Moving the piston from the BCG to the gas block requires the addition of an op-rod. Since nothing is taken away from the original design (which really isn't a DI system and does have a piston) the addition of the op-rod does add mass. Perhaps just a few ounces, but it's location moves mass further from the CG which increase the arm of that mass. It takes more effort to start and stop the mass when going from target to target, making the rifle slower. The advantage is it makes the swing smoother. It's up to the individual shooter whether or not it's good or bad or if it even makes a difference.
The elimination of the op-rod does not guarantee greater accuracy, but it does remove a possible variable. Re-introducing the op-rod doesn't mean it will hurt accuracy but it does have the potential for having a negative affect on barrel harmonics or other variable. The only way to be sure is to actually shoot it. As you point out, much of making a hit rests with the shooter. There are very successful snipers in history that used the Mosin Nagant and a 2.5x scope, a combination that while effective in the right hands, is not known for pinpoint accuracy.
While moving the piston from the BCG to the gas block reduces the amount of fouling in the BCG, it does not make the rifle cleaner. It simply moves the point of deposit to the gas block. Fouling at the gas block has no less an affect on reliable function of the rifle. I have never tried a op-rod upper on an AR, but I have put many rounds through other rifles with the piston located in the gas block. It can still build up to the point that reliability suffers.
As far as recoil feeling different, I agree with you. So what? The recoil of a AR carbine feels different than a rifle length AR, which feels different than FAL which feels different than an M14 and so on down the list
I'm not sure I get it, it seems kind of wishy washy....are you advocating your weapon/system or just showing it off to us? Its a nice gun but what are you getting at......??
I'm not trying to do either. Just trying to give my experience with it. Like I said, it's sometimes hard to get non-emotional info on a piston gun. It's just a data point for something I was trying to gain first hand knowledge and experience with.
I prefer the threads where guys come and spout the " second coming stuff" so the mods can teabag them to my delight.
That may be why I took a break from M4C for a while. My personal opinion is that a subset of the gun crowd (online or otherwise) brings about the drama more than for my taste. This site is such a great resource so it's usually worth the effort of wading through some of the drama.
Words
Well said, and said more eloquently than I. I also appreciate the correction about the op-rod vs piston. I guess I was using the term generically (DI vs "piston") and not technically correct.
justlikeanyoneelse
05-30-12, 17:03
Hey I appreciated your post, on a forum we especially need first hand experience. While I agree that carbon fouling is just moved to the gas block, Id rather have it there than inside.
Be careful what you say split66, saying stuff like that will get you tea bagged, this isn't a college frat house lets try to be professional.
Dwsmitht343
05-30-12, 17:39
Nicely done good points to think about by the op and mistwolf. My first ar purchase has been a piston system and I am still reading and learning. I plan to get a di weapon to compliment the piston one. Nice sbr by the way!
OP, thanks for the rundown on your piston build! It was refreshing to see you had no performance problems and put to bed some of the myths about next generation of .556 AR....at least on your SBR. Many people wanting a piston AR will be glad to view your post.
I'm not sure I get it, it seems kind of wishy washy....are you advocating your weapon/system or just showing it off to us? Its a nice gun but what are you getting at......??
I prefer the threads where guys come and spout the " second coming stuff" so the mods can teabag them to my delight.
HA!
Now that you mention it - SO DO I!
And to the OP, why did you build a piston SBR?
And to the OP, why did you build a piston SBR?
I mentioned it in my original post.
A primary reason for my interest in a piston gun was to gain experience with one personally and make my own decision based off my own uses.
One thing I enjoy about shooting (kind of like flying) is that no matter how good you may be at one particular discipline/platform/etc, there's always so much more to learn. I had no experiences with an "oprod" gun. I could read about it on the internet or I could learn firsthand. I chose the latter. Hopefully I can run it through its paces at a competition in June and see if it survives. I don't see a class happening for it for at least another year or more, unfortunately.
At the end of the day, it's a tool. It may be a fun tool, but only the end user can determine if it's a valuable tool for their needs.
That's nice your adams arms conversion kit works. Great!:smile: Shoot it and enjoy it.
I've seen and handled firsthand plenty that haven't. :(
It is my opinion that these are some of the flaws (as always, YMMV):
-They cost more than the parts they replace.
-They include parts of largely unknown quality (I believe they do from my experience, but have no data or documented evidence to back that up. However, their Adams/Spikes melonited m4 barrels of once upon a time should be a good indicator).
-The recoil is absolutely more noticeable. You added reciprocating mass, what do you expect?
-It lacks a fixed front sight, and instead utilizes a cumbersome railed gas block. Sweet, I get to use a cheezy flip up front sight when I just wanted a simple, reliable pinned A2 FSB! (Yes, some complete uppers have a pinned version of the railed gas block. That's not available in the kit form).
-If the gas block is canted by the slightest the op rod seizes. Which is a handy feature considering the gas block is neither low profile nor protected under a handguard.
-And it's only compatible with certain handguards. Other handguards can be made compatible with. a. ****ing. dremel. Might as well flute your barrel while you're down there.
-Speaking of gas blocks, be sure to keep your regulator lubed or you could allow enough crud to build up around it, making it difficult to remove. When it's dirty, the op rod may not follow the regulator out the front and instead stay stuck under the handguard.
-Also be sure that there is perfect, PERFECT spacing between the op rod and the carrier key face it impacts when you install the kit. Anything more than a fraction of a millimeter, but less than a sheet of paper may result in cycling issues. Spacing is critical when securing the gas block off the shoulder of the barrel near the gas port.
-It requires you to either buy a proprietary adams arms upper receiver OR hammer a steel sleeve into the gas tube port of an existing upper receiver, essentially barring you from ever using that receiver for a DI build in the future (until that sleeve rattles loose and cuddles with your FCG).
-You CAN use an existing bolt carrier with their gas-key replacement piece, but expect that to loosen up and/or shear off after a time (it's a $75 replacement, and I'm ignoring the long-term viability of acquiring replacement parts from the company) so you'll probably be using their (now included with the kit) one-piece carrier that has an enlarged radius in the rear to band-aid the carrier tilt issue and, since many guys using these kits are probably using questionable-source upper receivers and there exists a good chance that the receiver's inner diameter is undersized to accommodate the mouth-breathing "look at how tight my AR's tolerances are, I need a hammer to field strip" nonsense, there's a decent chance your carrier will be tight in the receiver. (Yay for run on sentences!) I haven't seen the one-piece carrier shear off the gas-key thingie, so that's an improvement.
-Cam pin gouging/dragging in the upper receiver shows how short-sighted the concept of piston retrofits are, however the cam pin eventually stops cutting away aluminum. Some spend even more $ for the POF roller cam band-aid.
I'm sure there are plenty of kits that run OK and might not experience any issues. Doesn't change my observations and opinion. YMMV.
TL;DR? "$15 gas tube? **** that, here's $300!"
I quality read on the pros and cons. Thanks for taking your time to write this up. The ar I am building is going to be an op rod one. The one after will be standard.. if I ever get money saved to finish it.
OP, thanks for the rundown on your piston build! It was refreshing to see you had no performance problems and put to bed some of the myths about next generation of .556 AR....at least on your SBR. Many people wanting a piston AR will be glad to view your post.
Most piston AR's use an HBAR type profiled barrel. Why? Barrel flex.
BCM AR's typically shoot around 1.5 inches at 100yds. So a gun that is generally capable of this type of accuracy and now shoots 2-3 inch groups is not a positive for the piston system (FYI).
C4
wishy washy = rambling post of observations without a point.
I'm not attacking the OP but asking "what is the result of these observations?" Is it better? Did it piss you off and you are going back to DI? Does your piston AR give you a tingly man chubby every time you rack a round? ANYTHING!
All I saw was " its different" or I dont have enough experience to tell you"
How can you compare weight? Any idiot can make an AR heavier than its supposed to be. Pull out the scale...show me.
How can you compare recoil? Give us some feedback head to head to head.
How can you compare dirtiness? I can f up any AR with enough ammo. You fired 700 rounds through it........in one year.
give me some meat...that is what this place is all about!
Please tell me your feelings, give me some substance. Data points are available on any AR website. Google "piston driven AR15"
As for the college vs professional site you are correct and I am sorry I used that term.
carry on
I like the weight argument. I havent weighed my AA upper and compared it to my Stag, but just holding it in my hands, its not the first thing that comes to mind.
A lot of people give me crap about using fixed iron sights over an optic, and I give them the same response you wrote. I dont need a $500 Eotech because Im not in Iraq clearing houses. Plus Im cheap.
Nice looking rifle.
Added reciprocating mass does not increase recoil, nor does it mean sharper recoil. If it did, a bolt action rifle would have softer recoil than self loading rifle
Piston AR's are all about give and take. Theoretically more reliable? Yes. Actually in practice more reliable? Ehh... Not really. Heavier? Yes. Less accurate? Yes, that's just physics. It isn't as bad as everybody makes it out to be, however. But, if you're a person who doesn't have to hump the thing hundreds of miles and hates to clean your gun, it can be a decent option.
I drank the piston cool-aid before I found this place, and my experience is the piston is relatively unimpressive. There's really no "real" reason for it, and the gun runs great in DI form. If you aren't an operator, and have money to blow, go for it.
Most piston AR's use an HBAR type profiled barrel. Why? Barrel flex.
BCM AR's typically shoot around 1.5 inches at 100yds. So a gun that is generally capable of this type of accuracy and now shoots 2-3 inch groups is not a positive for the piston system (FYI).
C4
I see...thanks Grant.
While moving the piston from the BCG to the gas block reduces the amount of fouling in the BCG, it does not make the rifle cleaner. It simply moves the point of deposit to the gas block. Fouling at the gas block has no less an affect on reliable function of the rifle. I have never tried a op-rod upper on an AR, but I have put many rounds through other rifles with the piston located in the gas block. It can still build up to the point that reliability suffers.
I am going to respectfully disagree with this, with the disclaimer that the only piston gun I know is the HK416, so there might be variables in regards to the conversion kits.
The upper and lower reciever in an op-rod AR design is cleaner than the inline piston system. The net fouling in a op rod system is less than in the inline piston system.
You state the the dirt accumulates in the gas block. I usually swab out my gas block after shooting, with a q-tip dipped in CLP. It might be a bit grey, but really no fouling to speak of.
There is some fouling on the barrel itself, on an area a few square milimeters just in front of the gas block opening for the piston, under the op rod. There is also some fouling around the gas evacuation port in the front of the gas block, where the front sight sits. There is also a bit of fouling on the piston itself.
What is the dirtiest part of the gun after shooting? Inside the hand guard, in the area that surrounds the gas block, where all the evacuated gas goes.
Some gas escapes as the piston moves to the rear, some gas is blown out of the evacuation port, and since we have the AGR (adjustable gas regulator), there are also some vent holes on the left side of the AGR selector where some gas escapes.
And this gas is blown out into thin air, and there is only fouling in the areas I mentioned. Most of it accumulates inside the handguard, like I stated.
In the inline piston, the gas is blown directly into the BCG, as you know. The C8 I shot, we ran close to 1200 rounds through it. M855. The BCG was DIRTY. So was the inside of the upper.
Having shot courses of fire exceeding 1200 rounds with the HK416, the amount of fouling is not directly comparable to the amount of fouling in a inline piston system. Not even close.
I am also going to disagree on the accuracy statement. The inherent accuracy of the weapon will of course be affected by the barrel harmonics, as well as microscopic variations in powder shape and weight, and projectile dimensions of the ammunition used. That is why a gun shot from a mechanical rest won't put rounds in the same hole. These variables however will not greatly affect accuracy. Mostly shooter error and inconsistency is the reason for increased group size.
But to state that the groups will double in size from a inline piston gun, is a bit of a stretch in my opinion. Our guns are 1 MOA from the factory. I have shot 1 MOA groups with my gun @100 meters, but that was slow deliberate fire from a bipod rest using a S&B Short Dot.
But at least the accuracy part would be easy to compare, if someone had similar setups, one inline piston and one op-rod gun, with the same ammo.
I know my MR416 is sub MOA capable. Matter of fact I think that with a more capable shooter then myself, it would be at least 1/2 MOA capable. It is 14.5 inches and has a .7 diam pre-gas block barrel and a .74 diam post gas block barrel FWIW.
Can't speak for any other piston design though.
Added reciprocating mass does not increase recoil, nor does it mean sharper recoil. If it did, a bolt action rifle would have softer recoil than self loading rifle
It's actually the opposite. Heavier buffers give "softer" recoil. Adding reciprocating mass is just like adding an even heavier buffer.
My personal opinion is that a subset of the gun crowd (online or otherwise) brings about the drama more than for my taste.
So, instead of adding this to an existing general piston-gun thread, you decided to start a NEW one...
....providing a lodestone that will attract them like iron filings.
....while providing neither new information, nor new lines of inquiry.
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