I’m looking at purchasing a Colt M16 bolt/carrier to replace that nasty shaved unit. The bolt is marked MPUC. The MPC is what I’m used to seeing, so what does the U signify? Thanks.
can’t help you, but maybe you can help me- where do you get colt parts? all i’ve ever seen is takeoffs and odd lowers on gun broker
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Look at Specialized Armament as noted in the previous post. Colt parts are also available from Brownells if you look under the factory parts heading.
dont worry the “U” is just date code.
my Colt bolt is marked MPGC 
Thanks for that…makes sense.
Someone on TOS (I think) contacted Colt about the markings. They would not disclose what the additional markings meant.
What the hell does “that nasty shaved unit” mean???
That means the carrier is the “half circle” variety, commonly referred to as shaved or lightened. They are half circle all the way back to the rear of the carrier. Colt made these to clear the sear block they used to put in rifles, and they changed to the M16 full circle carriers sometime in 2004 or 2005. There were some photos around here not too long ago showing the differences.
I bought a 6920 right after the ban ended in 2004, and the carbine’s build date was march 2004, and it came with that “nasty shaved unit.” That is in the process of being remedied as I type this.
Merry Christmas to all!
1/2 circle Colt carrier unshrouded:
1/2 circle Colt carrier shrouded:
AR15 full-circle unshrouded / AR15 enhanced shrouded / M16 carrier
Colt has a lot of variations in the way they mark their bolts.
Some of the more recent bolts even have the “MPC” ground down and a large “C” engraved over it.
Thanks Molon. Great photos. 
Yeah, I gotcha guys, I know the shrouded vs unshrouded bcg, but I just haven’t heard the term “shaved” used before.
On another note, those rather odd methods of Colt “MPC” markings are quite intertesting. I don’t think any of mine have those little “dots” used for the lettering. I always knew Colt had numerous ways of marking their bolts, with different letters/etc, but those oddly shaped dotted lines are new to me.
What’s the deal with those? I cannot think of any method Colt could/would use, that would result in those mis-shaped dots, which make up the letters. What’s up with that? I mean, it almost looks like a blind 3 year old with a tiny punch was let loose on those letters. Why are they so oddly shaped??? Anyone know what process was used for that???
Agreed here.