Fireforming 300win. mag cases

[scpaul]

I'm in the process of building a 7mm wildcat on a 300win. mag. case. Body taper and shoulder angle are both going to be changed pretty drastically. I'm wondering about the C.O.W. method generating enough pressure to do the job completely. Anyone that has experiance with this method of case forming and a suggestion of powder and amount would be appreciated. If it isn't feasable a light/medium fireforming load w/bullets is always an option; powder and amount suggestions on this method would also be appreciated. Thanks, Paul

 

[scpaul]

Has no one reformed 300 Win. brass ? OK is there a rule/thunb re: the C.O.W. method (case volume, pressure required, % of case volume increase, reduction of bore, weight/volume of C.O.W.) Any info. will help, I don't want start with nothing. I've seen info on smaller cases, guess I could increase proportionately to pressure/case volume. :-X

 

[bigedp51]

scpaul

I would forget the COW and just fire the cases with a bullet seated long and centered by the throat. Below is an animated image of a American SAAMI commercial .303 British cartridge being fired in a British military Enfield rifle. On rimmed and belted cases the shape of the cartridge case forward of the rim or belt is not critical as the case does not headspace on the shoulder.

Below is a brand new unfired Remington .303 case in a Wilson gauge. This case is being supported by the rim in the Wilson case gauge and would be much further into the gauge if the rim didn't stop further movement.

Below the fired case in the Wilson gauge showing how far the shoulder location is forward in the military chamber.

I fire form these cases with a reduced load using pistol or rifle bullets to fill out the upper body of the case. And again they are fire formed using a bullet to "center" the forward part of the case with the throat of the chamber. Without using a bullet and using COW your case will decide where the center and axis of the bore is. This could be the start of warped, off center and banana shaped cases.

Once your "belted" cases are fire formed then forget the belt and let the case headspace on the shoulder using the proper shoulder bump.

Rimmed and belted cases are from a bygone era of sloppy manufacturing tolerances and a belt is something you use to hold your pants up when they do not fit correctly.

They are from an era when Cordite powder was loaded into the case and then the shoulder and neck of the case were formed "after" the powder was placed into the case.

 

[scpaul]

Thank you, I had never heard/thought about the fact that the COW method could allow the case body to be formed off center, very good point! I had planned to disreguard the belt once they are reformed and basically necksize only, bumping the shoulder only as necessary. The one thing about the COW method is it's cheaper and doesn't require a trip to the range. (I do love spooking the neighbors.I live in an old neighborhood where making a little noise doesn't hurt, might work in my best intertest in the long run.I'm known as the "crazy OLD phart at the bottom of the hill".) When I buy the reamer, If I specify a no turn neck spec., would/wouldn't this help minimize the amount that the case could be formed off center? With a no turn neck am I playing with the possibility of causing a neck splitting problem on some batchs of brass?This will be my first wildcat,can't you tell ; I do appreciate the input/advice. Thanks again, Paul