Markings are the "C" on the extension at about 1:30, the MVP under the FSB, and "12" out near the muzzle. Forged no-drain FSB.

Was it just friday afternoon at Colt and this just got turned around backward in the M stamping machine, or was there something else going on?

Any insight appreciated.

Looks like you just found the holy grail of Retro barrels! The super rare "W" Prototype barrel!

I have one exactly like that. I just thought it was normal lol intersted though

If it was normal we would call them WVP's, right?

I dont think its special (other than its mine ) but I was just curious what others thought.

I had one stamped like that too.

I'm not so sure that a machine stamped the M and vp. Could have been a hand held stamp. I say that because I've seen quite a few of them that have rather randomly placed/skewed stamps. I would think that if they were machined stamped, that the barrel would have been placed on a V block or some other means of location. I could be wrong though. Anyone have any knowledge of how the proof marks were actually placed?  Based on some of the proof marks that I've seen, where the stamp was obviously placed above/below centerline, I'd say they were hand stamped.  If that assumption is true, it would be easy to have the stamp upside down.
As an aside, over the last 30 years of doing machine work, I've often had a stamp 180 out, but I don't think I've ever had one 90 out.

what's up with the screw in the swivel?

Interesting, thanks  

Just how I got it, not sure if it was done during or after its life in .gov service. Im going for a bfpu type build so Im leaving it

Mine is stamped straight. But the C is upside down at 12 o'clock.

I think it might be fair to say that the M and the Vp were stamped in two seperate operations, perhaps at different times. I'm basing that assumption on the fact that sometimes the M and Vp are side by side.........or said another way.......timed the same on the barrel. Sometimes one stamp is rotated around the barrel from where the other one is. That would, or might imply, that they were stamped at different times. It would seem to me that once the barrel was placed in/on whatever held it while it was stamped, that if they were both stamped at that time, that they would be indexed the same. I would think that the procedure to magnetically particle test the barrel might be done prior to assembly, and the Vp would be stamped after assembly........after the barrel was proof fired. (the Vp being the stamp for "verified proof")
I did a search on Vp and came up with this picture, which I believe is from an olf American Rifleman. My google foo and computer skills are lacking, so the discription under the pic didn;t come though, but it stated the gentlemans name in the pic, and stated that he was stamping Vp on these 1911's. Could have been done differently by the 60's, or not.
 Edit........see, no computer foo. The excerpt did come though.

Good insight, thanks for posting!