Forming .257 Wby cases from other brass

[The Sodbuster]

I have some 7mm Rem Mag and .300 Win Mag cases I'd picked up at the range.  Since they're based off the .300 H&H, as is the .257 Wby Mag, I thought maybe if I run 'em through my Weatherby sizing die, I could form them into brass for my Mark V. 

The 7mm mag cases went through the die easy enough and look right, although the necks are short.  With the .300 Win Mag cases, about 1/3 of them have serious dents or are crushed enough that they're useless.  Those that came through look right, but they'll obviously need trimming.  Although they do all have tiny creases in the brass where the case tapers down to the neck.  Am I wasting my time with this?  When I resize .30-06 to .25-06 I first run it through a .270 Win neck die before putting it in the .25-06 die.  I'm afraid I don't have a .270 Wby die for this intermediate step with my Weatherby case-forming efforts. 

Guess I should have tried chambering some cases before posting this.  I'm afraid to try the resized .300 Win Mag cases, and the 7mm mag cases look short.

[bubbadoyle]

I have used alot of 7mm mag brass in my 257 weatherby .  Yes the neck is a little short but they shoot just fine for me.  Just be careful as my 7mm brass weighs a good bit more than 257 weatherby brass, so case capacity is reduced.

[Tom W.]

Be careful of the "donut" on the neck, as this, if not trimmed, could cause serious pressure problems. I was going to try a simillar thing, resizing a .338 win mag to a 7mm Rem mag. The only difference that I could find was the caliber , as all other dimensions were the same , except from the head to thrbottom of the neck. When I did  it, I saw that the neck had a "donut". As I don't have an outside neck trimmer, I didn't want to take any foolish chances.

[Castaway]

Fire form the buggered up cases with about 10 grains of Unique topped with a wad of toilet paper and you can increase your yield.

[Stimey]

Fire form the buggered up cases with about 10 grains of Unique topped with a wad of toilet paper and you can increase your yield.

 Are you doing this fire forming with a bullet in the case, or just the touilet paper?