No it's not the gas block or ability to put the the correct hand guard. I believe the issue is the collar location, I know the true mk 12 barrels have a taper from .720 to .749 where the collar goes. That taper I know the dpms does not have but I think the location of that taper is further up the barrel towards the muzzle on a spec barrel than the dpms. Taking material off is doable and I'd imagine not to expensive. My thing is I am not building a "mk12 clone" I just really wanted to use the ops inc brake/collar, allen suppressor and have the rail end before the gas block like on the mod 1. If I can't do it then I may need to consider getting a different barrel. I want to build my own version of the spr with moe rifle stock, dual charging upper, mlok rail and the ops inc/allen set up.
@ killer86,
Yeah that's where I saw that the dpms won't work.
I might end up needing to use a aac spr/m4