Q: I’d like to develop a wildcat cartridge by necking down Remington’s 7mm SAUM case to shoot .264 calibre bullets. Can you tell me if this has already been done? If so, what kind of velocities could I expect with bullets weighing from 120 to 140 grains from a 600mm barrel? Do you think I’d do better to using the 7mm WSM case? Any comments about this would be appreciated? Where would I get dies for this new wildcat?
A: I have no doubt that as soon as the 7mm RSAUM arrived on the scene, wildcatters pounced on it with shouts of glee, necking it up and down to just about every conceivable calibre. They necked down the .270 and 7mm WSM cases to 6.5mm as well. Most experimenters consider the Remington case a better design than the WSM case. Although the former holds slightly more powder, the latter features a longer neck and is more efficient. Loaded to equal pressures, the WSM case delivers 2 to 3 percent higher velocities than the SAUM case, but burns up to 10-percent more powder to do so. Forming cases is as easy as falling off a log. Simply run 7mm SAUM cases into a full length die, trim to 2.025″ and deburr case mouths inside and out. There’s no need to ream or turn case necks. Being overbore capacity, the best powders for this wildcat are slow burners such as RE22, RE25 and AR 2217 sparked off by a magnum primer. I’d expect muzzle speeds of 3400fps with the 120gn bullet, 3300 with the 125gn, 3250 with the 130gn and 3100fps with the 140gn. Loading dies for this “new” wildcat are available from Redding and RCBS. Of course there’s little or no loading data available so working up loads is done by trial and error. Unless you are an experienced handloader, I recommend you give the 6.5-7mm RSAUM a miss.