AR-10 5.56 Nato Conversion
My father and myself were having a discussion about AR's in general and he asked me whether or not you could use an AR-15 upper (5.56 NATO) on an AR-10 lower to sort of have the best of both worlds. I've crawled the net for a little bit on the subject and really I pull up a bunch of stuff on AR-15 conversions and not much on the AR-10 conversion.
My questions are: 1. Can you easily use your AR-15 upper on an AR-10 lower. 2. Do AR-10 5.56 NATO conversions exist and where are they?
Thanks for the help.
No it won't work. The AR10 receiver is longer and larger than the AR15. There are even different AR10's and uppers won't interchange between the different AR10's.
Gunco Good ole boy
The Fulton Armory Titan (308)and the DPMS LR308 will interchange. Neither will fit the Armalite, though.
As stated above, the .556/223 platform is much smaller than the 7.62/308 so a conversion wouldn't work.
Why would the AR10 lower be better?
Gunco Addicted for life
there is no reason that an AR10 lower would offer any advantage over the smaller ar15/16 lower in a 5.56/223 set up even IF it fit the smaller upper.
Originally Posted by 
this is an "answer" in search of a question.
The "question" would be can you build a "poor man's SCAR" by starting with the larger magwell of the AR10 and use an adapter for AR15 mags.
IMO it could be done with the right amount of research and scrounging. A magwell adapter would probably need to be machined or a scrap mag used as the starting point. But I agree it is an answer in search of a question - caliber-conversion platforms are presumably an interchangeable platform for "on the go" applications... but who wants to carry a backpack full of gun parts around?
IMO you could do better. I've seen a lower with a slide-in mag well, allowing you to swap calibers by using additional shims for different mags/calibers. That would be the best solution as you could use different mags with the uppers. Can't remember who made it, just saw it and said "neat" then moved on.
Back in July 1984 "Gun World" magezine did an article on the A.I.I. Inc A.R.C. conversions for the AR-15 lower frame. These were 9mm and .45 ACP steel uppers for the AR-15 type lowers. They mounted the mag out the left side like a Sten. These were pistols and SBR's for LEO sales. When Bob Pierce (A.I.I. Inc, in Prescott, AZ) went out of business I obtained some spares with which to experiment. Fun stuff !!! These were all blow-back pistol conversions.
In discussions with a friend who worked with Pierce I learned that there was a prototype .308 conversion unit for the AR-15 lower. Yes, that's right !!! This was done with the square steel upper using a side-mounted .308 magezine and I assume a locked breach. Wish I had some pictures of that unit. This all transpired over 20 years ago.
I've been messing with converting an AR10 to 7.62x39 as the larger magwell might be able to fit AK-47 magazines.