Been there & done that about 8 years ago.
PPU 7X57 brass from Graf's.
Neck down to about .290 OD using .260 R die without expander/decapper with die backed way out so no contact with shoulder.
Lube inside necks with powdered graphite, then neck down to 6mm using 6mm Rem die with expander/decapper, some brass spring back happens
Turn necks to .268 - .270 OD (.270 - .015 - .015 = .240, bullet diameter = .243)
Fire Form COW (cream of wheat or cream of rice, raid pantry).
Decap & clean & inspect insides of brass for FF debris.
Anneal - toast with propane for 1 min
F/L size using 6mm Rem or 6mm AI die without expander/decapper - working on uniformity & run-out concerns with annealed brass.
Trim & chamfer necks. 7X57 brass is a tiny bit shorter than 6mm Rem but trim to make uniform.
I took about 1 week to process 100 & used them for about 8 cycles. No problems but lots of work.