On the left and center are two stainless OTP barrels and on the right is camo anodized barrel which could be Carter.
OTP stainless barrels look very similar to early Dye Stainless barrels but there are a few differences.
If you look at the end of the bore/muzzel break there is an inch long portion that is a larger inner diameter.
Some of the muzzle breaks on the stainless OTP barrels have lines milled into that run parallel to the barrel. The center barrel is an example of this cut.
Let me know if there are other differences I am forgetting.
Both of the stainless barrels pictures are super polished and have the larger ID portion under the muzzle break. I will probably will end up putting them on the Brahim Ironmen bodies I am putting together.