Alpha and the Hornady srp brass use large flash hole. Lapua, Peterson use small and the strongly advise NOT to open them up. Although I really see nothing wrong with the idea. I have not tried it yet, as I haven't had any issues. I have not shot in sub zero temps yet.I never thought of enlarging the flash hole highdrum.
I only have a few left and will try that.
Do you use a flash hole deburring tool or drill it out?