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.
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.
