I have a 200 rd. batch of weatherby 270 bee cases (made by norma) that have been loaded dozens of times, and trimmed once, in a factory chamber. they have been partialy resized each firing, and loaded to book max.
RR

I use; 1. Lee Collet Neck Sizer Die 308 win. 2. Forster Bench Rest Full Lenght sizer Die 308 win. 3. Forster Ultra micrometer Seater Die 308 win.
I do not exclude the possibility of error to have me, but it`s probably bad brass l got.
Always follo manufacturer of black powder.
Which is now only used Lapua and RWS in these two caliber.

Using blackpowder in a smokeless cartridge may be your issue...

Use only powder Vihtavuori N540 because Varget not always.