Barrel Fins - Colt Vs Others?

[Sig]

Anyone able to post clear photos of Original 1921 early compensator barrel fins Vs other types of barrel fins?

I am looking at a Colt 1921AC Thompson (sorry working remotely right now) with an early compensator and an alignment or witness mark. The finish matches the gun as far as I can tell yet I thought the fins were thinner than what I am seeing. Compensator is clearly no mark and the thinner barrel end. Sorry not able to post pics right now, otherwise I would.

[LIONHART]

Early '21 Guns have thinner fins than later ones. Fins on a Colt Gun are more rounded than WW2 Fins. WW2 1928 Fins are more square. some WH Barrels have rounded fins, and I think the new Kahr 10" Replacement Barrels have rounded fins as well.

[gijive]

Sig,

 

If you attend the TCA Thompson Show and Shoot next year you will see that the fin thickness varies on the Colt guns depending on when they were made. It seems that the earliest guns had very thin fins, yet I've seen some that have slightly thicker fins. The Colt guns that had the barrel replaced with the second style compensator definitely have thicker fins.

 

If the gun has the first model compensator the fins are usually thinner, but I'v seen the fin thickness vary. One way to get an idea is to count the fins. The Colt guns should have 29, not counting the flange at the breech end. The first model compensators have a different thread pitch than the second style, so if the compensator looks legitimate and the retaining pin doesn't look tampered with, chances are it is the original barrel.