Castboolits.gunloads is a good site if you haven't been there.
Find discussions on bore size etc. All guns bore size vary. Regardless of model or make. Tooling wear etc. if you really get into it. Need to find exactly what you'd bore size is. True with modern cartridges also. Might be a little different than you would imagine. Something you force down the bore is different. Unless you are blowing something 1600fps or higher. Gas checks aren't needed. Heavy large boolits don't get there usually.