This may have been hashed out before but could not find anything on it.I was wondering why it states in the owners manual (the one I downloaded from this site) "DO NOT exchange or switch bolt assemblies from one M16A2 to another doing so may result in injury to. or death of, personnel"  I got both of my AR's without instructions. I happened to do this once because while at the range I found my ejector pin missing so instead of driving 50 miles home I just switched bolts and carrier around! Was this a close call? Thanks for the help!!!    

DrB.

As long as the head space is okay, you should be fine.  The military does it all the time.  If you make it a regular thing, be sure to get a set of headspace guages to always keep yourself in check and make sure you don't have  kaboom.  If you don't have the guages, the best thing to do is avoid swicthing them cause you never know.