AR parts commonality between brands?

[KAPA]

Was searching around and couldn't find much on this... Can anyone tell me if i can switch out parts between two different ARs and expect them to run just as good as with their original parts? For example, a Colt 6920 is known to be fairly loose while a Sig M400 is known to be pretty tight. Could I swap out parts between them and expect them to run just as well? What about between two 6920s or two M400s?

I suspect my answer is going to be "not as well" but would they run well enough to be considered reliable?

[brutal]

With the exception of upper-lower fit on a factory matched rifle that might be a little better than a mutt, MILSPEC is MILSPEC. You're going to find most everything will fit to one degree or another. AR's are like Goldilocks and the Three Bears but with size instead of heat.

All things being equal - BCG, buffer spring and buffer, there shouldn't be any reliability issues.

[HoneyBadger]

MILSPEC is MILSPEC.

+1. This is the point of standardization: Anything that complies with MILSPEC standards is interchangable.

[KAPA]

Nice! Thanks for the replies guys.

[Great-Kazoo]

ALWAYS CHECK HEAD SPACE if and when you switch bolt assy's around.

[KAPA]

ALWAYS CHECK HEAD SPACE if and when you switch bolt assy's around.

What does that mean exactly?

[ray1970]

What does that mean exactly?

He means just because headspace is good with one bolt doesn't mean it will be with another.

[kidicarus13]

Maybe he doesn't know what headspace is.

[KAPA]

Maybe he doesn't know what headspace is.

Yes, that was the problem.

http://en.wikipedia.org/wiki/Headspace_(firearms)

Interesting. Is there any method of checking headspace without the use of a tool or gauge? Seems like the measurements are so small you can't with the human eye or will the BCG just not be flush with the rear of the upper?

[ray1970]

Special tools required. Unless someone knows a trick I am not aware of.