Has anyone ever done a definitive accuracy test of the two systems? Specifically, as regards the ‘Modern Gas Piston System’, like the PWS Long-throw Piston System. When I do a Google search all I seem to come up with are the tired old Gas Piston vs DI which is better, cleaner, more reliable arguments. I've already made up my mind. I like piston guns. I'm not interested in re-hashing those issues. However, I am interested in pure mechanical accuracy potential of the two systems. There seems to be a lot of anecdotal statements out there stating emphatically that DI systems are 'inherently' more accurate. Where's the test data?

I haven't seen any legitimate empirical testing, where both systems are tied down to a Ransom Rest or some equivalent and fired for groups. Every argument seems to end with, "Well, if a Gas Piston AR can shoot more accurately, it would be used at Camp Perry." I don't know if the Camp Perry Nationals are the 'be all, end all' of rifle accuracy, but it seems to be the final say when discussing AR Gas Piston vs. DI, especially in the 'Service Rifle' category.

Before the AR-15/M-16 came to be, gas piston rifles like the M1 Garand and the M14 were pretty popular. And of course, the DI AR-15 supplanted those older piston system rifles. Is the DI system simply more accurate than ANY gas piston rifle?

If, the definitive answer is "Yes", then the question is moot. I'd still like to see the data. However, if you are talking mechanical accuracy measured in the thousandths, then an argument can be made that environmental conditions and the person behind the trigger can negate any possible mechanical advantage of one over the other.

I’m just curious.

Old_Navy

There is no functional difference in accuracy for well made systems.

Haven't seen a lot information on this, but from what I own (both types) I have seen that the accuracy is pretty close for similar setups, when comparing parts apples to apples.  For instance, don't expect my 10.5" piston SBR to outshoot my 20" match grade DI setup, etc.

If you want to see some data on it, go out and create some.  Then post it up.

Best regards and stay safe,

B

My one thought is there is a small, lucrative and loyal industry built around DI 'Service rifle' shooters. You can sink an enormous amount of money chasing a tenth of and inch.I read a statistic that Gas Piston gun sales on average make-up about 15%/year of all AR sales and in a good year maybe 20%.I can't really provide a source for that statistic, so take it with a grain of salt. I'm just wondering if there is a company considering fielding a shooting team to take on the DI guns at their own game? Or, maybe I'm just behind the times and "3-Gun Competition" is the 'new thing'. I understand gas piston guns are well represented in those competitions.

It also dawned on me after I wrote the OP, maybe Gas Piston Guns are not legal in the 'Service Rifle' competition? I don't know.

As I said, I'm simply curious if there is any definitive accuracy data out there. Since I'm not a competitive shooter this is strictly an intellectual exercise.

Old_Navy

If the purpose of a free float rail is for no pressure on the barrel doesn't an external piston mechanism attached to the end of the barrel defeat that purpose?  As the piston is activated its going to transfer force to the barrel that its attached to.

Built rifles for my brother and a good friend at the same time.  Brother went AA XLP piston, buddy went DI because that's what he was familiar with from his Army days.  Otherwise they both used the same Voodoo 18" fluted match barrel, the same MI SS Gen 2 FFHG, and have the same triggers installed.  They both shoot under 3/4" at 100 yds.  We haven't strapped them into a sled to split hairs, but there is NO functional difference between them.

If you think about the system there is no discernable difference between them, because of timing.  The projectile has left the barrel before the piston is actualted.  Because of this accuracy is not affected.  In shooting both the only difference is the recoil impulse, but down range there was no difference in accuracy.  A sled taking humans out of the equation could change this, but real world says it's not worth fretting over.

jbooker82...good point. However, I think there is some level of barrel harmonic 'interference' even with a standard DI Gas Block and tube. Maybe not as much? Or, maybe the Gas Block and gas tube introduce additional 'stiffening' the barrel assembly? Although, everything else is basically the same as long as you get a Gas Piston System that doesn't induce a lot of BCG tilt and drives it back as straight as the DI system does. And that may be the Achilles Heal for 'Piston' system.  

As far as doing my own testing. I don't have the resources to perform quantitative/qualitative testing to ensure a large enough statistical sampling to be meaningful. Wish I did. Unfortunately, it requires deep corporate pockets to do that kind of testing.

Best regards,

Old_Navy

Mr. Brain...thank you for the thoughtful and informative response. I appreciate your real-world knowledge. What I read on the 'InterWeb' are opinions often tainted by an almost pathological investment in one system or the other.

I'll be perfectly honest. The ONLY reason I went to Gas Piston gun is I hated to clean my DI rifle. I had my '2005 Bushmaster M4'gery converted by ADDAX Tactical in '2008 with an early version of the PWS system (different design than the current system). I know it's a petty and trivial reason, but it's the truth nonetheless. I currently own a PWS Mk114 Mod1 carbine in .223 Wylde. A wonderful little gun.

BTW, I still have that Bushy 'ADDAX conversion' and have no noticeable BCG tilt.  The rifle shoots great!

Best regards,

Old_Navy

Well see the thing you also have to take into account is barrel regidity, barrel cut, barrel length, type of piston system, torque specs, and how the barrel mates to the upper. All of those to my knowledge will have an effect on accuracy.

Speaking from my own experiences I have been able to shoot tighter groups with my M6 IC than I have ever been able to shoot with an M16A2 or an M4. I got tighter groups even without an optic. Whenever I qual on my M4 I have used the CCO and even then was still not able to achieve tighter groups than my own personal rifles. That also probably comes down to my trigger choice as well considering I use GA triggers in all my AR15's.

One of my favorite things to do is dispell myths about piston rifles by taking people to the range with my own and letting them shoot their own groups.

Everyone likes to talk about my rifle is 1 MOA and sub MOA but look at the conditions this kind of shooting takes place. It takes place in stress free ideal conditions with the rifle mounted on a bench usually utilizing rests on the front and sometimes rear.

Of course you're going to shoot more accurately under those conditions but for me personally if you want to talk about accuracy I take the stance of combat grade accuracy. If your rifle can shoot 3 - 4 MOA under stressed and unideal conditions it is G2G in my book.

Most rifles especially ones tuned for accuracy with specific loads in most cases will shoot better than the actual shooter.

The kind of accuracy we typically talk about on this site is outside the realm of a good number of shooters capabilities including mine.

Could I possibly shoot 1MOA with my rifles? It's very likely if I took my time and did it in ideal shooting conditions. Do I do it? No. A lot of shooting I practice for is reactive based shooting where it's about getting an acceptable kill group on a target quickly.

That kind of shooting will not give you 1 MOA or sub MOA accuracy but it most asuredly will keep you alive.

However all this changes if we start talking about different shooting roles such as snipers, DMR's, and hunters. That's a different kind of shooting one that I believe although is proven to be possible with an AR either DI or piston is one that is not something goal wise you should be aiming for IMO.

If that's your goal go for it. I'm not stopping you but to use a quote from the .mil forum "the war I train for is different".

The quality of the barrel and other components has a much greater effect on accuracy than DI/piston. Either drive system is capable of sub-MOA accuracy.

^^^This.

Not trivial at all... I'm with you.  No other firearm system that I own injects heat and expended gases into its action.  As a lefty it was a Godsend because a wet DI gun spatters my eye protection with oil.  I also prefer grease and I can run that in my action and almost never have to change it, excpt when I get solvent into it and break it down.  It doesn't burn off like oil does in a DI.

So, don't feel the least bit guilty.  All my guns are piston driven for these reasons, are all very accurate, and I can dump mag after mag if I so choose and never get the BCG warmer than the temp outside.  I see no downside to it.

Mr. Evil...As I stated earlier, I'm not a competitive shooter. Nor, am I a target shooter. I shoot for pleasure and to keep my skill-set reasonably honed, so if forced, I could protect my loved ones and myself, in the event of a serious social matter.

Like you, my ruler of success is, can I cover the group with the palm of my hand? At my age (60) and with health issues (stroke survivor), my eyes don't let me shoot MOA in the best of circumstances.

In the Military I learned 'a little ditty'. "Two in the chest, one in the head, even the Jolly Green Giant will be dead."  It has something to do with a Southeast African country. I can still do that at CQB distances.  That's good enough for me.

Thank you  and all the others for contributing to this conversation. I like discussing things of interest (at least to me) in a civil and adult manner. I hope I convey, I'm not trying to gore anyone's sacred cow.

Best regards,

Old_Navy

As I said, I appreciate the discussion. There is one piece of information I knew, but had forgotten. I was reminded by one of the contributors, the bullet is out of the barrel
long before a  'Piston, or DI gun for that matter begins to take the action out of Battery.  So, any criticism of how the 'Piston' influences the accuracy of the gun in a negative manner is moot. At least IMHO.

Old_Navy

That is a fair point!

You can raise BS flag but I dont care, I shot a 3 shot (yes not a five shot whatev) group with my Sig 716 gas piston that measured 0.75" inches at 200 yards.

168 grain Barnes TSX over Varget. RRA match trigger group, gun was sandbagged in.

I think thats pretty good for a piston gun.

I believe it. I shot a guys gun that had a well used RRA match trigger. Single stage, no grit or take up. It was by far the smoothest trigger I've shot outside a GA. Me personally though outside of pistols I hate single stage triggers. You have to break that trigger in or polish it to experience the full benefits in my opinion.

Mr. J-L...3/4" a 200-yd. Impressive. I'm not a good 'Groups' shooter, it wouldn't matter how mechanically accurate the rifle is. But, there are those who can shoot 'bug-holes' if the rifle is up to it. Good on-ya Mate!

My first outing with my new Mk114 Mod 1 after sighting-in, I shot 3" extreme spread group at 100-yd and was very happy. When I performed the basics and held my tongue right, I even got a couple of bulls-eyes. Considering it was a brand new rifle, new Vortex PST 1-4 x 30 scope and new American Defense QD mount and it was also raining, cold (56-degrees. For FLA it's cold) and the wind was gusting to 25-mph, I'm thrilled with the results. Certainly good enough to put food on the table and to stop any that would try to take it away.

Best regards,

Old_Navy

I've noticed no difference in groupings from my GP Huldra or DI BCM, both 16" middy's.

The whole "piston guns are inaccurate" is bunk IMO.

^^^This.

To that end, any truly anal Engineer would and could argue that on a DI platform, the excess gasses jetting out the side BCG's gas ports imparts an off axis force. Off axis forces, even minute, is never good for shooter accuracy.

Ditto what Herr Evil said in the extended post.

I could say my DI is way more accurate than my piston ARs and that would be true
Of course the DI I am talking about is a White Oaks 26" barrel 15 pound prone/bench gun with an adjustable Geissele match trigger, PRS stock and 10X sniper scope but it certainly is a DI and more accurate.

Now, I have a couple of DI M4s I love. My SWMP15 TS (expensive for a SW) is so light and handy and I recently got a deal on a nice lightweight Aero Precision with YH hand guard and popup front site, Troy rear and Magpul stock for 5 bills, (who could pass that up?)
They both are light and shoot as well as my PWS MK114s.
So, why is it I almost always shoot the PWS?
I keep my training mags pistols and ARs loaded and everything ready because I live 2.4 miles from our club and can decide to shoot and be loaded and on the road in under 10 minutes including beverage. When I go to the safe what I see is the fact I will be coming home and with the PWS I will be putting the gun right in the safe 9 times out of ten while the DI will get stripped and cleaned.

That is all the reason I need to want a piston over a DI as there is no performance difference in accuracy or in short range trips reliability issues.

Now, if they would only make a pistol that does not need a cleaning save every 2K rounds