In all my reloading I never collapsed a shoulder. I am back in the saddle after a decade of not reloading. Anyway, I got some never fired 7mmRM brass, and sized it in Redding dies to 257WM, I did not neck turn or ream, people said here not needed by there experiences, 7mmRM brass is about 1/16" or .0625 shorter then 257WM brass after the change, they will not even reach the crimping groove in the die if the die is set to touch the shell holder when the ram is fully extended All cases where chamfered.
I set the bullet seating die correctly, seated, 12 bullets, Hordnady 117gr RDN with the crimping groove, the next 3 seating attemps collapse the shoulder. The next 5 went okay. Need opinions and knowledge here.

Are you trying to crimp as you seat the bullets? Variations in case length or too tight a crimp setting will collapse shoulders on cases. Even new virgin brass can have length variations. If you do not intend to crimp, perhaps your seating die is in too far and the crimping shoulder is bumping the case mouths a bit. In either case, you may want to back off the die body a bit and see if that solves your problem.

Crimping, if you want to do it at all, is probably better done as a separate step, and a Lee Factory Crimp Die is your friend.

Other possible causes could be failure to chamfer the case necks sufficiently or case necks that are too thick. When you size 7mm brass down to .257, it wouldn't be unusual for the case neck walls to thicken as they are sized down. That would require reaming or turning to correct.

You using the expander ball when forming the .257 Wby brass from 7mm Rem?

John

Maybe you're doing it wrong?

Hondo,
Yes I had the expander ball in the 257WM die when I resized them.

257,get over it!!! If you cant be part of the solution, you are a problem!!! I never do anything wrong,sometimes incorrectly, but never wrong!!

Haha. Glad you edited that from what you probably first thought about me. Since I didn't know the solution, I figured you needed a light moment. A deep breath, maybe. I hope you get it solved. But at least now I know why I sprung for factory 257 Roy brass.

Are the bullets seating hard or does it take normal tension to seat them? I've seen the shoulder move back a few .001 on my 30-378 because the die leaves the case mouth extremely tight for seating bullets.
If the bullets aren't seating with alot of effort I would have to say something is going on with a crimping feature of the die or other internal problem with the seating die.

257H,
Na Heaven, it was an add not an edit. No hard feelings by me!
I do not think it is the brass persay. It cant be the crimping ring in the die either because the cases are about .060 shorter then a regular factory 257WM case and never even touches the crimping area of the die. I think it was/is the shoulder got formed in the die to the radiuses of a WM and may have been worked a bit, and/or the inside diameter or the neck is tight even though the expander ball went through them after the neck is sized on its outside diameter.
But looking for any posible ideas, I have ever had this happen before, BUT I never took a different caliber brass to form it into something else except for fire forming 257R to 257AI.

If the seating tension is normal compared with other cases you reload for I doubt it is the shoulders just collapsing. What is the inside mouth diameter after sizing the case? Anything smaller than .254/.253??

IME, it dosen`t take much to collapse the Wby design necks. I`ve done it on my 7`s.
The flat base bullet has got to be guided by hand into the neck. I know you said you champered, IMO, you can not over champer, so check that. Also sounds as the next cases seated fine.

All else fails, shoot boat tails!!but I`d check champering..

Not a bad idea. Stick a 100 Gr TSX in there and go kill stuff. They will act like they're as heavy as the 117 grainers but at a higher velocity