Here is how I did it. I used a deep 12 point 9/16 socket, it fits my 300 WBY cases perfectly. The drill is a cordless. I made sure the flame was adjusted the same each time and the same distance from the case. I will know if I did any good when I test them Saturday.
The rifles in the pic are my 300 WBY (nearest) and .308 I built when I was in the Marine Corps as a police sniper rifle
I took the 300 out last Saturday to test some loads at 300 yards. It was hot as heck out 90+ so the mirage was an issue, had a light switching wind as well. That said the rifle wants to shoot. Of the 27 rounds I fired 23 were pretty good to excellent. I think the rifle will agg. 1 in with this load at 300 yards in perfect conditions, if I do my part.
I am shooting 210 Berger's at a little over 3000 fps with 80 grains of 7828. The groups on the right are .010 off the lands and on the left they are .020 off.