Quote Originally Posted by RCS View Post
Jeff, I was able to check this early upper and heavy barrel over this weekend. The upper has the Colt triangle and square C in front of the ejection port, no FW or brass deflector. The ejection port cover looks just like the 604. The slip ring is flat. The rear sight drum has only an arrow R.

The barrel is .680 at the muzzle, .715 in front of the front sight base and .750 between the bayonet lug and swivel. I checked the barrel again, it is 1X12 twist. The barrel has the exact profile as your photo of the Model 606 profile. The handguards are the glossy black triangular.

I have plans to get this upper/heavy barrel back as I think it is kind of a rare item. Thanks for your help and posting the photo of the 606 barrel profile
Does the upper look like this, no numbers on the sight wheel, just an arrow R and no arrow on the reciever itself?