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Posted: 2/23/2007 12:46:20 PM EDT
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Should have just posted here in this forum for the higher visibility but...hindsight is 20/20. Anyway, post recreated below for convenience sake: www.ar15.com/forums/topic.html?b=3&f=4&t=316662 I had a question that was recently fielded to me, and I've never built an AR before, so I'm kind of curious of myself. "Are all AR15 uppers and lowers interchangeable?" I know for the most part the answer is yes, but are there any exceptions? I remember reading somewhere that Colt's civilian rifles weren't made milspec and therefore there might be some compatibility problems with milspec parts? Finally, can a gas piston upper work with a lower that was originally part of a direct impingement rifle? Thanks. |
| For the most part yes all lowers and uppers fit together fine. Colt is the only exception to the rule. Colt made some uppers and lowers with a larger front pivot pin. Of course they don't do that anymore, just on some of the earlier AR-15's. And yes you can add a gas piston upper to a standard lower with no problems. |
You WILL find that some receivers are "tighter" than others, starting with RRA. They did this on purpose; their lowers are a hair narrower in the pivot ears and their uppers are a bit wider in the pivot lug. The takedown lug is also just a bit bigger. All of this gives you an incredibly tight rifle when it's put together, but it can be a bit of a chore to get it together in the first place. 
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| Also, some of the parts for a Bushmaster Carbon Fiber AR15 are not mil-spec, and therefore cannot be easily interchanged with some others. Old Professional Ordinance CAR-15 carbon fiber rifles have very few mil-spec parts on them. Uppers won't match mil-spec lowers and vice-versa (the takedown pins are not located in the same position) also the barrel nut is different on some of these rifles. gk |
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