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Transplanting an hk piston assy

3829 Views 8 Replies 8 Participants Last post by  CoolHandPuke
This may sound nuts... Has anyone ever built an AR using an American barrel, lower receiver and upper receiver but retrofitted the HK piston system (gas block, piston assy, barrel nut, 'channel' tube (metal cylinder which passes through the upper, providing a channel for the piston rod to go through the upper receiver and impinge the bolt carrier), and bolt/carrier assy?Looking for a project!Thanks!Charles
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My understanding is that the HK416 is reliable not just b/c they put a piston in an AR-15 but it was developed and tested as a piston driven AR-15 and is a complex upgrade. The buffer and recoil assembly are optimized for the 416's performance. Putting a piston into a mil spec M4 will probably result in a compromise and for M4 PIP, the US army has dropped the piston conversion. For a weapon to be reliable the whole package must be properly designed, integrated and tested. If you want a piston AR-15, it's better to buy an upper receiver that was developed and tested as such. If you can't get a MR556, then LWRC may be a good choice (I don't have experience with LWRC guns but they did get a DEA contract and there have been good reviews).

If the American made barrel is not a CHF barrel, then it will have shorter service life and will probably rupture earlier during FA torture tests (M4 light profile barrel launches a round through the side @ around 540 rounds, the HK416's CHF barrel will survive after 900 rounds). Also, I heard HK's CHF barrels have better performance and safety if the barrel is obstructed. But for civilians I think the stuff about barrels is less important.

It's best if you switch the HK lower for a standard AR lower so you can use reliable and readily available mags like Pmags rather than try installing HK416 components into an AR-15.
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