DI vs Piston AR-15

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DI vs Piston AR-15

Postby LumberZach on Mon Mar 13, 2017 9:06 pm

Certainly not learning anything new here, but I enjoyed this quick read and thought I would share it here.

https://www.ssusa.org/articles/2017/2/2 ... -accuracy/

Enjoy.


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Re: DI vs Piston AR-15

Postby Holland&Holland on Mon Mar 13, 2017 9:12 pm

While I do not disagree with his theory, it could just be that that particular barrel liked di better. A different barrel could give different results.
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Re: DI vs Piston AR-15

Postby UnaStamus on Wed Mar 15, 2017 2:00 am

Piston rifles have had a sordid past with accuracy. There have been problems along the way with several big name rifles.

The British Army was looking to develop a semi-auto rifle platform for their L129A1 Designated Marksman Rifle. The rifle solicitation came down to two main challengers: LMT 308MWS and HK 417. The LMT is DI and HK417 is GP. The HK417 had reliability issues, and the accuracy was subpar. The LMT was obviously chosen.

The German Army was looking at developing a Designated Marksman Rifle as well, designated the G28. They basically designated HK to build the rifle, and HK built an accurized HK417. The rifle failed the testing and couldn't hold the requisite 1.5MOA or better. After the rifle was rejected, they had to rework the barrel to get it to meet accuracy testing.

The Navy was looking for an SSR (Sniper Support Rifle) and FN modified the Mk17 and developed the Mk20 SSR. The rifle was built to be an accurate semi-auto, and it has difficulty printing better than 3/4 MOA consistently. I read a write-up on the Mk20 and it mentioned that several shooters ran it during the USASOC sniper competition back in 2014 or 2015, and the rifle had difficulty competing with the LaRue OBRs being run by most of the other competitors.

The harmonics are a major component to the accuracy. GP rifles require tuning to make them work. This is one of the reasons why you need a proprietary system with GP, so that the barrel and piston setup are able to function harmoniously. In contrast, you really don't need to "tune" a DI rifle so long as it's a free-float setup. Pretty much any quality barrel will produce accurate results. Custom designs like tighter receivers, different chamber cuttings and so forth can enhance the accuracy. It's not uncommon for a general build to pull 1/2 MOA or better. Custom or factory precision offerings like the JP LRP-07, GA Precision GAP-10 or LaRue OBR are printing 1/4 to 1/3 MOA groups consistently.

You can get a GP rifle to shoot well, but the accuracy of the GP rifles has always been less than DI. The question is really whether you will notice the difference between a 1/2 MOA gun or 3/4 - 1 MOA gun. 3/4 - 1 MOA is still very accurate.
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