While cleaning my new Preban Colt Sporter target, and my friend his Postban Colt H-BAR Comp. target. (both about the same condition)we mixed up the bolt carrier assemblies. One bolt has M P C etched into it the other has M P V C in white. Anyone know which one goes to which weapon?  Thanks, You guys are great!! I have learned so much here...

IT does not matter at all.

"MPC" came from the oldest firearm.

Thank You SBR7!! I was concerned about head space.

If you mixed up the CARRIERS, it doesn't matter.

If you mixed up the BOLTS, headspacing should be checked with a gauge before you fire the rifles again, just to be safe.

You might be able to determine which goes where by very thoroughly cleaning the barrel extension lug area and the bolt face and lugs as well, and matching up the wear marks.   It could work.  If one pairing clearly shows matching wear marks and a different pairing shows wear marks that DON'T match, then apparently the first pairing is the right one.

CJ