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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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Why? It seems unnecessarily complicated, invasive, and expensive (if at all possible). I can understand putting a custom made barrel in place of an MR556 barrel and/or using a non-HK lower, but the rest seem unnecessary.....assuming it's even possible in the first place.

...just my take on it; it's YOUR time and money.
 

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It would probably cost more then simply buying an MR556 upper due to the amount of work that would have to be done to the barrel, modfying the upper, having a custom barrel nut manufactured, etc.

And good luck finding hand guards that fit.
 

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There are several piston conversion kits. The short stroke piston is just one of the improvements HK made to the AR platform. Unless you can make the parts yourself, it wouldn't at all be cost effective to just try to install the piston setup. If you could even get the parts, that is. Check out gaspiston.com. A friend has one of the Osprey Defense kits and says it works great.
 

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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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Discussion Starter #6
Thanks for the input

Thanks to all who took the time to reply! This is more of a "see if it can be done" project for me. I am trying to adapt a seekins precision upper / gen 2 lower to piston operation (billet construction, ambidextrous bolt release, and it looks cooler).I have a couple 416 uppers and spare parts as well as lwrci rifles/parts. Having studied the retrofit piston systems, I've found them all lacking compared to lwrci and HK, so when I wanted to build my own piston gun, it was a natural choice for me to try to adapt one of these to my own upper. The HK was my first choice due to the firing pin safety system / no lite primer strikes and the beefier gas block. However, as several above have printed out, HK modified the receiver (beyond the piston channel, which is enlarged and incorporates a stainless steel insert, just like LWRCI) to include an indexing notch for the rail system. LWRCI uses a standard upper (with the piston channel). I'll post the progress...
 

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I would actually be surprised if HK hasn't explored the possibility of selling parts kits for just such a project. I don't blame them for not doing it if they have looked into it. It's a very flooded market.

Since you *have* to buy a full HK upper to do what you want, like others have said, I would probably just replace the barrel, if that's you're concern.
 

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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
That is in fact how the first HKM4's (HK416's) were developed. HK took US Govt "loaner" M4's and modifed them with an HK-made CHF barrel, op rod gas system and bolt group. The same was done with a Dutch-built original AR10 for the first shooting HK417 prototype. While it can be done I would not "try it at home". One of the drop in kits mentioned herein might be a better choice if you want to convert a DI gun to op rod.

G3Kurz
 

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Of course it can be done, the question is should it? Sounds like you're trying to get a 416/17 on the cheap; hell I can respect that. I'm sure it can be done, depending on your skill the results could be great or... inconsistent shall we say. If you do it, post some pics.
 
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