Need help identifying upper

**dentron** · 01-20-16, 14:44

I just picked up this upper reciever and would like to know more about it. From the research I have done, I believe it to be a 603 or 604 model. It has C M forge code and the barrel is marked C MP CHROME BORE. It does not have a forward assist. I think it has a larger diameter front pivot pin hole. Square C proof mark, no marks on FSB. Does have dust cover. Has bird cage FH.

Any info would be great.

Pictures:

**herd118** · 01-20-16, 14:51

It's a Colt SP1 (semi-auto,commercial) upper.

**mack7.62** · 01-20-16, 14:57

Also know as a big hole due to the pivot pin being larger than normal, use on a standard sized lower will require an adapter.

**Renegade04** · 01-20-16, 14:58

What you have is an Colt SP1 upper assembly. Not a 604. The 604 uppers did not have the .315 hole for the pivot pin. Only the SP1 uppers did. 603 uppers have forward assist. I have the exact same upper assembly on my 1977 SP1. The C MP CHROME BORE barrels were used starting in 1974. M16A1s used the same barrel up until production ceased (around 1982). The C M forge code is for "Colt / Martin Marietta".