I've used kg gunkote and nic cerakote on several front lug bolt rifles.
With a good airbrush and some practice, you can 'fog' into the breech area and get surprisingly good coverage. I've popped a barrel off and looked. I do it last, thin a bit with mek or acetone, turn the air down, and take my time.
Gunkote is thinner than cerakote (0.35 mil vs 1 mil), and is also slipperier and I've had no issues when coating absolutely everything, though these are not super close tolerance actions like nesikas or bats.
I have some duracote and armacote I bought for non-bake parts but can't really comment on them yet