Case Forming?

[Ben Lamb]

I've also heard that one can use about a half case of Bullseye with NOTHING in the case mouth [no tissue, etc.] and obviously point it straight up. Doing a lot of cases might give one a dirty barrel. I prefer a stout load and the bullet lightly jammed.

That would save a lot of burger.

 

[Caseknife]

Good question. Guess we're going to see.


That's what I do for my .257 AI-- 117gr Interlock on top of a moderate load of whatever I have handy to blow out the shoulder. Have used Varget, StaBall 6.5, maybe even Win 760 with good success. I'd like to follow the same procedure to form these 25-7 cases but I'm back to my chicken or egg problem-- I don't know how I would seat the bullet without already having the die I would be ordering using the once-fired brass. I wonder if I can get a 7PRC bullet seating die with a .257 seating stem by itself?

If you are using the 7PRC as the parent round, just use the 7 PRC seating die to seat the bullet. If there is any inconsistencies it will come out when it is fired. All you are doing is making a couple fireformed cases to base the die making process off of, you are not looking for accuracy. If it is a moderate load and the bullet is kissing the lands, the brass WILL form to the chamber.

 

[Caseknife]

That would save a lot of burger.

What I want to know, is the burger you use mixed with 20% suet and does it stick together when cooked down the barrel?

 

[kodiakisland]

Good question. Guess we're going to see.


That's what I do for my .257 AI-- 117gr Interlock on top of a moderate load of whatever I have handy to blow out the shoulder. Have used Varget, StaBall 6.5, maybe even Win 760 with good success. I'd like to follow the same procedure to form these 25-7 cases but I'm back to my chicken or egg problem-- I don't know how I would seat the bullet without already having the die I would be ordering using the once-fired brass. I wonder if I can get a 7PRC bullet seating die with a .257 seating stem by itself?

If it was me I'd just get the 25 WSSM dies. You are already into this project by a lot, so what's a little more?
Use those dies to neck down the 7mm cases with a false shoulder for positive headspace. Load a cheap bullet with the WSSM dies and go shoot. You are only after 3 fired cases, so ultimate accuracy is not the issue, only proper formed cases.
Use other people work and extrapolate what you need to. Should be fairly easy. You just end up with expensive dies you used 3 times. https://westtexordnance.com/25-7-prc-cartridge-development-and-test-results/

Or, trust the die maker has the correct dimensions and forgo the fired brass all together.