When I chamfer flash holes, I begin my trimming the brass to a uniform length.
I then set the stop by adjusting it so that it trims away the metal flashing the flash hole punch leaves behind, but not deeper. I attempt to avoid leaving any bevel in the inner end of the flash hole.
IMHO, this directs the flash directly along the case axis, and extends the the flash's reach as deep as possible into the propellant column.
IMHO the best internal burn pattern is along the case's central axis, from the center line toward the case wall. I believe this generates the most consistent pressure curve.
Mine is mounted on my RCBS case prep station, and interchanges with the pocket brush depending on whether dealing with new or fired brass.
Greg
PS Don't get upset about the brass in the picture. My first few batches looked exactly the same until I learned better. Yours will shoot and likely be accurate as well. I just believe the no-bevel approach ends up better.
You will probably find, as I did, that as a beginning handloader, all your skills will improve (be more consistent) concurrently. This means that any issues due to the beveled flash hole will likely end up being perceptible on the target as your consistency with all those other skills reaches a better level. It's not a big deal, and nothing has been ruined.
When you buy Lapua and pay the premium, this part of what that extra buys. It really is better, but if one chooses to prep their own brass, and does it well, it's a tradeoff between luxury and sweat-equity.
Just go forth and sin no more, youngster.
