I just recently got a custom 257 Wby and have had a bit of an issue fire forming 7mm Rem Mag brass to 257 Wby. Although there are a number of threads floating around where this is discussed, I haven't seen any that include load data. No problem with chambering or firing but I can't seem to get the rounded Wby shoulder to form.

What I've tried so far is two different loads: 1.) 100gr Rem SP with 65gr RL19 and 2.) 120gr Rem Core lokt with 67gr RL19, both loads were developed using virgin Peterson brass and fresh Remington mag primers. The reason for RL19 is nothing more than "I got some" and "I don't use it much anymore." I found load data for RL19 from Nosler online. Min/Max loads for 100gr bullets with RL19 is 65/69gr, and for the 120gr min/max is 61/65gr.

On the left is a piece of unmodified 7mm Rem Mag brass, on the right is one that has been run through my full-length sizer, loaded with 67gr RL19 and a 120gr Rem Core lokt.



Brass looked much the same with the lighter load (65gr RL19 and 100gr bullet), which is why I increased bullet weight and powder charge, which is actually 2gr over max book load from Nosler. One more detail, I checked velocity on the 120gr load and I'm at 3200fps out of a 26" barrel.

Should I be using faster powder to fire form? Could freebore be the issue here?

I have used Rem. and Win. 7 mag brass and have never seen anything approaching what you show. Either after full length sizing or fire forming. Wby MKV and RCBS dies. What does the weatherby brass look like after firing. Something is not right with your setup.

What 219 Wasp said.

Here's what happens when I run 7mm Rem. Magnum brass through my .257 Weatherby die:



And no, the case has not been fire-formed.

Yep when I form 7 mag to 257 it goes right through the die and loads and fires perfectly. I would anneal the 7 mag brass if you have not already that will make a big difference.

Thanks for the info guys. The approach I took to sizing brass was fairly cautious - gradually adjusting the die downward until brass could be chambered but with a little pressure on the bolt handle. After full length sizing, I've still got a false shoulder in the neck and not much, if any, rounding of the shoulder. I'm using a new set of Forster dies.

I'm still surprised that a load hot enough to push a 120gr bullet 3200fps won't create this shoulder.

I have not annealed my brass, but it looks like Peterson brass is annealed from the factory.

After reading the posts from Mule Deer and 219 Wasp, I set my sizing die up according to factory recommendations - dialed down to the shell holder, then 1/8 turn further - and resized a fired case. This case was previously fired with the 67gr RL 120gr bullet load. At left in the photo below is the case that's been sized a second time, at right is a once-fired case.



Seems odd that a properly cut 257 Wby chamber could produce the case on the right.

Looks like a .264 Winchester reamer was used. How does a bullet fit in the fired case?

That's a good eye you've got there 219. I checked and a .257 bullet is pretty sloppy in the neck of the fired case. Then I checked a .264 bullet and I can press it into neck of the fired case just with hand force. It's tight but I can push it in and pull it out with my fingers. ID of the fired case (at right in photo above) is 0.264 and ID of the newly sized case is 0.255.

Quick question for the fire.

Is resized 7mm as accurate as 257 Weatherby brass? Is there any trimming necessary. New brass is tough to come by right now.

Thanks

Onerifle

You have to watch neck thickness.

DF

It should always be checked to make sure there's no problem with your .257 Weatherby chamber, but so far all that I've necked down has resulted in loaded rounds with more than enough neck clearance in two .257 Weatherbys, a Vanguard and an Ultra Light Arms Model 28.

Dumb question but you mention it’s a “custom”….is it actually bored .257 or .264?

Something isn't right for the OP with the pics he has posted.....................................

.

Have you measured it?

Yeah,...there's something wrong with the OP's procedure.
I just did a bunch the other day for my son's 257 Wby
Look like this out of the die and loaded with 110 Accubonds
Necks are about .060 short but they will work.

Onerifle, I find most 7 mag brass has necks just a bit tighter than the WBY .257 brass but still gives enough clearance. Rem and Win brass is heavier so powder capacity is a bit less.

Wasp

What brass would you recommend for long term use?

I gotta buy something to hold me over.

Thx

Onerifle

I had checked it with a bullet before firing and it seemed to be 0.257, however checking with calipers it seems to be 0.264.

I like the Weatherby brass. Case capacity matches the data better. Got 60 pieces when I bought the rifle in 1990. Probably only 200 rounds fired but all the brass is still good. I tend to use full power loads! The gun has never been a tackdriver. I am in the Ingwe camp regarding the Mark 5. A buddy bought a new one in 257 3 or 4 years back, it doesn't shoot great either.

Another dumb question….Were you firing your fire forming loads at a target or just firing them into the dirt? If they were at a target, were the bullet holes circular or slightly oblong?

Isn't weatherby brass typically made by Norma? I think mine may be stamped Norma. Of course its possible the have switched suppliers.

They were fired at a target, much key holing was observed - most came through sideways. However the barrel is 8 twist and I suspected stability issues were due to jackets spinning off.

So your smith built a 264 mag and marked it as a 257 Weatherby? Think I'd be having a few choice words with said gunsmith, followed by not using that gunsmith again in the future!

That’s the reason I asked the dumb questions. 😁

Damn. Would be really bad if that were reversed and the owner was able to chamber a round and light it off. Yowzers!!!

I appreciate all of the "dumb" questions that I didn't think of myself!

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