Forming 6mm Rem from Norma 7x57 Mauser brass

[AckleymanII]

I neck turn at 7mm, then they neck down to 6mm very easily, then do a clean up cut at 6mm.

On the AI's, I leave a small section, forming a false shoulder to keep headspace tight...never loose a case.

 

[fyrewall]

I have a .260 Rem die, I use that on 7X57 PPU cases but remove the expander ball and adjust the die so the shoulder of the 7X57 brass just stops short of contacting the inside shoulder of the shorter .260 Rem - just the neck - a neck reduction of about .020- (don't squash the 7X57 shoulder back). Shoulders of the .260 are slopey and act as sort of a funnel to guide the brass in to the die neck. Next step is to run the brass into a 6mm F/L die for final sizing. If the ammo is to be 6mm Rem I use the expander ball, then neck turn to .268. If it is to be 6mm AI, I size without the expander ball in a 6mm Rem F/L die (it gotta fit inside the chamber with a slight crush fit), then fireform to 6mm AI (COW), then size with a 6mm AI F/L die with expander, then neck turn to .268. I use a small amount of 3 in 1 Lock Lube inside the case necks.

Neck turning only 1 time.

Sort of a pain but you only gotta do it once. Annealing the finished product helps.

 

[Lannister]

If you have a 257 roberts die run the 7x57 through that then into your 6mm and trim. If you do not have a 257 die run it straight through your 6mm die then trim. Use a good case lube like imperial sizing wax. After its trimmed put it in your gun to see if it fits nice. If its too tight you will need to neck ream or turn. Im not sure if you would need to aneal after. It couldn't hurt though. Good luck, i'm in the process using 7x57 to make 257 roberts. I found that i don't need to neck ream. You could make the 6mm out of 257 a little easier but 257 is pretty hard to find too and its expensive.

 

[fyrewall]

I gotta add - subject the fired round to a simple bullet slip fit test. If a bullet does not easily slide into a fired case the neck of that case needs to be turned. Upon necking down from an inside bullet diameter of .284 to .243 the brass has to go somewhere and that makes for thicker neck walls. Upon firing that case in most chambers there might not be enough neck space to allow enough expansion, like bullet grabbing.

 

[AMG04]

I run 7x57 into a RCBS 6mm Rem die. Fireform, then trim and neck turn. I use Redding Type S dies for subsequent sizing and bullet seating.