The Firing Line Forums - View Single Post - why a difference in load data between manuals

Clark · November 5, 2010, 04:23 PM

The 308 uses the 1889 7.65x53mm Mauser case head built with large Boxer primer pocket.

In 1905 the 8x57 was sending a 150 gr at 2900 fps, which we know today takes that the same case, but with Berdan primer, to about the same pressure that limits the case head with the Boxer primer.

This case head is good for 65k ~ 70kpsi before short brass life in handloads for an individual rifle.

The 270 and other cartridges using this case head were registered at SAAMI as 65kpsi average peak pressure many years ago.

We would have thought that the 308 would have been registered at 65kpsi, but it was registered at 62kpsi.

More recently, the 260 with this case head was registered at 62kpsi, maybe because there are manufacturing variations and different rifle variations for factory ammo in unknown rifles.

The SAAMI registration and loads should be designed to stay a safety margin away from the weak link in the system, the large Boxer primer pocket.

But that is reality and pressure measurements and published data has taken on a life of it's own.

Often in engineering there is a polarization of two political parties; "follow procedures" and "get'r done".

This polarization in reloading strong rifles, like the 308 would then divide us into two parties, one trying to find the one true load book to follow with load book fundamentalism, and the other camp finding the threshold of short brass life and backing off a safety margin.

November 5, 2010, 04:23 PM	#12
Clark Senior Member Join Date: December 4, 1999 Location: WA, the ever blue state Posts: 4,678	The 308 uses the 1889 7.65x53mm Mauser case head built with large Boxer primer pocket. In 1905 the 8x57 was sending a 150 gr at 2900 fps, which we know today takes that the same case, but with Berdan primer, to about the same pressure that limits the case head with the Boxer primer. This case head is good for 65k ~ 70kpsi before short brass life in handloads for an individual rifle. The 270 and other cartridges using this case head were registered at SAAMI as 65kpsi average peak pressure many years ago. We would have thought that the 308 would have been registered at 65kpsi, but it was registered at 62kpsi. More recently, the 260 with this case head was registered at 62kpsi, maybe because there are manufacturing variations and different rifle variations for factory ammo in unknown rifles. The SAAMI registration and loads should be designed to stay a safety margin away from the weak link in the system, the large Boxer primer pocket. But that is reality and pressure measurements and published data has taken on a life of it's own. Often in engineering there is a polarization of two political parties; "follow procedures" and "get'r done". This polarization in reloading strong rifles, like the 308 would then divide us into two parties, one trying to find the one true load book to follow with load book fundamentalism, and the other camp finding the threshold of short brass life and backing off a safety margin.