I had this problem with my .260 Remington build. Because a lot of manufactures through the term ar-10 around interchangeably so often, I got a barrel and a bcg that were both advertised for ar-10s. After it wouldn’t close on a no go gauge, I did a little research and found out my problem was ar-10 barrel to dpms style bcg.
because I had custom ordered the barrel, I sent it back with my bolt and they fixed the head spacing issue. The thing is a little tight when trying to manually extract a round, but fires, extracts, ejects, and is really accurate.
so if you have the option, instead of getting an armalite bcg, you can go the route of fixing your chamber and headspace.