Thread: Case head separation imminent

Originally Posted by grandpamac

Greetings all,
I currently have two sets of .223 Rem sizing dies here so I thought it might be useful to compare their sized cases. I selected two once fired cases that had been fired in my old Brno. Each was de capped with a punch and base set and one sized in each die with the decapping stem removed to eliminate one more variable. The case were then measured in the comparator and the RCBS die set the shoulder back an additional 0.04mm (a bit less than 0.002") which is actually quite close. With the RCBS dies I would need the +0.002 shell holder rather than the standard one
Next I hunted out a copy of the SAAMI chamber and case dimensions for the .270. The maximum case would be a slight crush fit in the minimum chamber which would be hard to notice in chambering but the minimum case would be a very loose fit in a maximum chamber at 0.333mm clearance (about 0.013"). This is enormous. The headspace dimensions for the .270 were taken from the .30-03, a forerunner of the .30-06. Later cartridges may have tighter tolerances but this reinforces the point that setting the die down hard on the shell holder is going to result in early case head separations in many rifles.
Regards Grandpamac.
Some cases are much more stoutly constructed and so may take longer to separate but separate they will in time if they are oversized.

That bit about the origin of headspace dimensions for 270 is very interesting - and the wide variation possible, esp considering it is a 65000psi max case. Certainly the Xbolt fired cases I was given were way long. I didnt worry about that too much figuring they could handle one stretch / fireform from new ( hope I was right), they were then sized to just chamber nicely in the old BSA Hunter and loaded with a light load ( start load of 2217 for 2660 fps 130 partition) to mimic a light 7x57 load.