When I crown my barrels, I don't use any dremel at all since I know it would be uneven. This is what I do....
I use a piece of masking tape and wrap the barrel to the approximate desired length. I use a marker and draw an outline on the masking tape to the exact length I want. I then use a hack saw and cut slightly more than my desired length since I know it will have to be grinded/sanded.
Following, I clamp the barrel vertically in my vise and use a filer to sand off the burs and rough edges. After sanding, the newly cut edge is still rough and crude.
I then clamp my inner barrel within a portable vise and place it underneath a drill press. HOWEVER, the inner barrel needs to be completely vertical or else the filing from the drill press will cause the edge to be slanted. I usually clamp the barrel right at the top to prevent any wobbling from the friction/sanding of the drill press.
I place a flat drill bit in the drill press to sand off the newly made cut and progress to a finer grid drill bit. Afterwards, I use a conical shape drill bit that just fits within the inner diameter of the barrel to chamber/crown the inner edge and again, i progress to a finer drill bit to crown the edges.
The final result is a cut to the inner barrel that is parallel to the length of the barrel with no slants, deformities, or uneveniness. The crowning is also very even within the inner ridge of the inner barrel. I don't need to use any sandpaper or dremel since I want to avoid the risk for human errors at all cost. Any slight imperfections or residual burs from the inner barrel can compromise the accuracy of the inner barrel, and as such, I avoid hands tools (except for the hack saw of course). I've used this approach 6 times, and achieved good results for all 6 attempts. Here is the what I did:
Marking the length of the inner barrel:
Cutting the inner barrel with hack saw
Drill pressing
Finished product
