I received the 601 upper that raised a lot of questions.  m1sniper and others had seen a lot of anomalies in the other thread which i captured in the notes below.

• square forge upper without proofmarks, though not as sharp as some square forge


• lacks recess around ejection port, the ejection port door does not close as securely and bumps open easily.


• finish appears original w/ darker shiny anodized lugs


• has normal 601 upper features (recess under ejection port, angle cuts above charging handle, hole for ejection port cover spring, recess on pivot pin lug)


• small parts appear original (sight wheel, ejection port cover)


• barrel extension not stamped (none of my 1:14 barrels are)


• barrel L marked but has Colt C in a square proof mark near the barrel nut


• cast FSB w/ correct C mark and uncoated sling swivel


• carbon steel gas tube

My best *guess* is that the upper was a replacement upper since it wasn't proofed.  That may be how one without the ejection port recess got out, as a replacement.  The barrel with the colt proof mark does lend a lot more credence to it being an original barrel that's just undocumented.

We have seen anomalies make it out before like 603 forgings that has the arrow and R ground down and engraved:

https://www.ar15.com/archive/topic.html?b=3&f=123&t=620690

OPs pics









My pics
C in square proof mark


In Ekie's guide


Rounder square forge like my other 601 upper


Not related to above upper but observations i found while going through my 601 uppers:

Pic of a more square forging and more rounded forging on 601 uppers


The more square forged upper in the pic above had the angled cuts on the pivot pin

Very interesting.  My personal belief from having handled a number of different 601 items is that they lack consistency on the finer points.
I think there are some valid generalizations about 601 characteristics, but the parts themselves were made over a number of years by
many different machinists.  I have also seen some weird lettering and marks on lowers and the barrels.  Part of this may also be that
we had both Colt and Armalite company parts coming together on one rifle.

Were you able to confirm the barrel twist?

haven't measured yet but was told it was 1:14.

Its a fake ill take it!
my 601 upper is more rounded too, but all the other features of a 601.

When u get a chance please confirm and share!

 

Here is another oddity, there is no slot for the charging handle latch machined in this "CH" forge Colt proof marked upper receiver:

Wow.

Made on a Friday?