Hi guys.
I had a question about Colt's compatibility with other AR15 manufacturers. I heard that something about them (don't remember what - the guys was kinda mumbling) is not compatible with other companies. Is this true? If so, what exactly isn't compatible?

Thanks in advance.

Some older Colts use .312" front takedown pins, instead of .250" like they do now and everone else always has. Some Colts have a block in the receiver that makes it impossible to use anything but a Colt proprietary bolt carrier. All Colts, even modern ones, use larger than standard fire control group pins, although essentially any factory or aftermarket trigger component you might what is available.

Colt upper, CMT lower, problem solved (at a significant cost savings).

Ahh, that's it. Thank you, Combat_Jack.  

Quoted: Hi guys. I had a question about Colt's compatibility with other AR15 manufacturers. I heard that something about them (don't remember what - the guys was kinda mumbling) is not compatible with other companies. Is this true? If so, what exactly isn't compatible? Thanks in advance.

Google for "large small pin colt bushmaster lower" or "lightning link colt doesn't work"