Just wondering what would be the proper 603/604 upper to go with a Colt MP 12 marked barrel. The FSB is a forged type with flashing removed and no drain hole if this helps. Also.........would these barrels have come with the early bend gas tube or the improved?  Thanks folks..........

Most would have left the factory with early bend tubes and square forge upper receivers.  A square forge upper receiver with the rebate underneath the port door would be optimal, but not required.

Assuming this ^ is what we're talking about....

MP12 barrels were only produced for a relatively short time and were in the timeframe when IMHO, from original examples Ive seen...uppers were sort of in between "very square" and "clearly round." They most definitely would not have been found on the rebated under the port door uppers.

This is the upper I have my MP12 barrel assembled on, and I feel like its the correct profile. Its what I would call a late square forge 604 upper. Notice how the left side is slightly curved at the top:



This barrel was originally assembled on an XM16E1upper that @Morg308 had that I believe looked the same. Also keep in mind with the MP12 theres about a 50/50 chance it would have been on a full fence XM16E1 lower.


^ Full fence lower indicating produced between Jan 1967-Oct 1967 Notice the curvature of the forge lines


^ Another example of the sort of rounded at the top forge lines


Compared to how straight the early uppers were (this upper is rebated under the port door)


This is an early A1 with the MP C barrel (all original, .fed gun)

Thats my case for how uppers looked from 66-69~ish and what MP12 barrels would have been assembled on. Mostly square but slightly rounded at the corners.

Thanks for the input gentlemen!!

MP 12 barrel is 1966 to 1967, refer to Ekie's guide for proper upper.

You are correct, my bad.  I SAW MP12, but I THOUGHT M VP 12.  Most MP 12 barrels WOULD have had early bend tubes, and they would have been on square to round uppers, but NOT square rebated uppers.

VP MVP MP CMPC .... It's easy to have a brain fart