Gunsmithing Is this the correct Devcon for action bedding?

I have used that tube stuff. It works ok, but it flows a little and as said, may shrink more. If you are just doing a skim bed it will work ok. I do not recommend it for a full bed job.
As for the milling part, the key is to bridge off areas you don't want the epoxy to go to reduce the need for trimming. But there is almost always a little trimming needed. For that, a dremel with a sanding drum will fit the bill.