Belted magnums

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mehavey
Why would you want to [re]size for Rim headspace rather than for shoulder fit ?
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A) The first shot of a piece of brass will be off the belt and not the shoulder. New brass come from the factory with the shoulder pushed way back.

To get around that you could mandrel up the neck, then partial neck size, and get a tiny shoulder that will stand up to the firing pin, but I don't know anyone doing that.

B) There is 0.010" variation possible in shoulder headspace from rifle to rifle per SAAMI tolerance. A piece of brass shot in one rifle, resized, and fired in another, could easily wind up spacing on the belt again.

C) You can't screw up and push back the belt too much, but you can have the die screwed too far into the press [too close to the shell holder when the ram is raised] and push the shoulder back too much. It may take as little as 0.005" shoulder push back to be on the belt again. With 7/8-14 thread on a die, the pitch is 0.071", so 0.005" adjustment is only 4 minutes if the die were a clock.... and you would be on the belt again. You can bet that mistake happens every day.
 
When full length sizing, headspacing (head clearance) a belted magnum off the shoulder, the area in front of the belt may become unsupported in the chamber on firing. Brass will bulge.
 
Myself, i full length size virgin brass. I've been burned by "once fired" before.
After that i collet neck size only.
My 7mm Rem Mags accuracy node is high up on the charge range.
I get about 6-7 reloads before the primer pockets work loose.
 
When full length sizing, headspacing (head clearance) a belted magnum off the shoulder, the area in front of the belt may become unsupported in the chamber on firing. Brass will bulge.
Click to expand...
No matter what, the rear of the case is going stretch back to meet the bolt.

Sizing to shoulder minimizes stretch -- which seriously and matter of factly
weakens the case precisely where a "bulge" can show thereafter up.

Size to the shoulder for strongest/longest case life/minimal bulge growth.
 
For decades, full length sizing fired belted cases bumping their shoulders back a couple thousandths so they'll headspace there when fired has produced best accuracy. But that ridge a few thousandths in front of the belt has to be sized down so it doesn't interfere with the case freely headspacing on its shoulder and cause accuracy problems by causing irregular barrel vibrations.

A standard full length sizing die had its top cut off below the shoulder and above the belt clearance then used after full length sizing all the way to the belt. The Willis collet die now does the same thing.

20 to 30 maximum reloads per case was normal.
 
This thread went inactive in 2015, until revived today. Pretty sure what ever the OP was going to do has been done by now.

Closed.
 
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