So I just bought this bolt off of the EE. Was supposed to get a BCM bolt ended up with this one with the letter MPXC on it. After doing some research I found that the "X" was a date code manufactured by Colt. But one thing that surprised me about the bolt is that it has a one-piece gas ring on it. Did Colt ever install these on their bolts from the factory? I didn't think so. Coincidentally I was reading through a document I downloaded here about the Navy's CQB 10" receiver. It appears that they used bolts with one piece gas rings in those. Can anyone offer any insight? Below is the document I am referring to.

http://drop.io/ogdfbvh

I dont know for sure but its probably a mcfarland ring or gapless gas rings.

Yea it looks like a Mcfarland. The document just says COTS, but that probably means Mcfarland. I thought that the armed forces stuck with regular three piece rings. I have read enough about the Mcfarland causing short stroking that I don't want to use it in my rifle.