Hey guys I'm in the process of collecting parts for an early Mod 604 build… BUT I need some input from you guys to know what kind of upper I should look to buy.

The BIG question I have is this... Did the early 604 rifles use the Mod 601 / 602 upper receivers where the milling just under the ejection port on the upper meets perfectly with the milling on the mag well of the lower?  OR were they offset on the early 604’s?

Any help you guys might offer would be greatly appreciated.

Brandon

The forge line underneath the port door on the early 604's are not offset. They're square forge as well.

Here's some specs and pics of my early varient and as I purchased older parts and installed them.

Click Here!

The earliest 604s were square forge and had the "early contour" under the port door where it did line up with the lower receiver.  HipSh0T's build below has a nice example of that style upper receiver, they are very tough to find and I have never seen one in person.  Later square forge 604 and all round forge 604 upper receivers do not line up under the port door.  SP1 upper receivers switch back and forth from early -> late -> early contour under the port door.  604 upper receivers used to be all over the place but I don't see them at shows or for sale on the EE as often as when I got into this.  (I think I've had an account since 2010)

Thanks for ALL the help guys... the picture examples really helped!  Looks like the 604 upper I have according to these pictures was made in 67/68ish.

I'm looking for something earlier if anyone has a lead?  Would prefer the 64/65 vintage but would settle for the 65/67 example for my build.

Thanks again!

Brandon

Great photos. I dated mine to the 67 on period too. I know my 604 build is a mix match of early and later parts.....but seeing as the USAF armorers did that........I guess I am good.   hahaha  

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If your not in a hurry than do what I did. Build a 604 and just keep upgrading it until it's all correct. The nice thing about the 604 is any configuration can be justified... Those uppers are NOT easy to find, I think it took me around 3 years to find the one I have.

Yep, I'm with ya on that... I'm in the process of collecting the correct early small parts to use on my partial fence NDS lower and 1967/68 vintage colt upper with the hope of upgrading later to an early upper.  I'm in no hurry because I want to do it right like you.

Thanks again for all the help guys!

Brandon