Is M4 and M16 (AR15) upper and lowers compatible?

[ShootAndHunt]

Just wondering whether the uppers and lowers of the M4 and M16 are compatible or not. i.e. could you put a M4 upper on a M16 lower, or put a M16 upper on a M4 lower?

I am asking this because they look alike, but there are also some differences, for example the buffer and the action return spring are very different, (and others please remind me), this may introduce some differences to the action function. will these differences cause any problem when you interchange the uppers and lowers of M4 and M16? Anyone has some experiences?

 

[Ed]

yes you can switch them with no problem. You can't switch buffer from M4 stock to M16 stock( unless is is a pinned M4 style with a full length buffer). So to answer your question yes. The upper has the same sized bolt so it will work.

 

[Mulliga]

As I read once on a post on ARF.com, the carbine-length gas system is compatible with the A2-length buffer, and the A2-length gas system is compatible with the carbine buffer (these guys even put a 20" HBAR upper on a stubby-stocked lower - no problems at all).

Pretty good design, no?

 

[Das Pferd]

According to http://www.isayeret.com/weapons/assault/assault.htm the Israelis have been switching uppers for a while. Instead of bying all new M4's, they retrofitted most of their old firearms with M4 uppers only to keep the cost down.