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Posted: 2/23/2007 11:46:20 AM EST
[Last Edit: 2/23/2007 11:48:11 AM EST by Agent_Scott]
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.
Link Posted: 2/23/2007 12:05:52 PM EST
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.
Link Posted: 2/23/2007 12:09:11 PM EST
Thanks GunDisaster. That's what I thought, but I wanted to be 100% sure before I passed on any false info.
Link Posted: 2/23/2007 12:12:08 PM EST
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.
Link Posted: 2/23/2007 12:14:18 PM EST
no, if you try it you will effectivly kill yourself. you can send all your AR stuff to mee for disposal

grins greedily
Link Posted: 2/23/2007 12:29:19 PM EST

Originally Posted By Shadowstep:
no, if you try it you will effectivly kill yourself. you can send all your AR stuff to mee for disposal


Heh...I'm sure I'll be fine.
Link Posted: 2/26/2007 8:12:16 PM EST
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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