I think what’s always held me back is figuring out the whole barrel populating thing and how to properly headspace. Just the whole process of how a already barreled to the trunnion orients itself into a build
If you are using an OG barrel, Trunion, and bolt, it's super easy.
Pop out the barrel pin, press the barrel out of the trunion, rivet in the trunion, press the barrel back in, put the barrel pin back in.
New barrels require drilling and setting headspace which isn't that hard.
I have yet to Populate a Barrel but i am not afraid at all as YouTube and people here are your friend.
All of my builds so far have been with OG Barrels already populated and all i do is like @Rabbit2047 said just pop out the Barrel pin and Press out barrel then Rivet the Trunnion in to a Receiver then press barrel back in and press barrel pin back in and all good.