6.5 Short Action Ultra Magnum

We will never know for certain who was first to neck down the 7mm Remington Short Action Ultra Mag case for .264-inch bullets, but George Gardner of GA Precision is the person who put the wildcat on the map. In addition to being a serious participant in Precision Rifle Series competition, he is one of its strongest supporters as well.

- Layne Simpson

George started using the cartridge in competition in 2012, and while it became only mildly popular there, it quickly caught on with hunters across the country. Many custom rifles have been built around the cartridge, with no small number of them put together at GA Precision. When Remington 7mm SAUM brass became difficult to come by, Gardner turned to Hornady, and that company has since turned out thousands of 6.5 SAUM cases, all sold through GA Precision.

As is often the case with wildcat cartridges, there is more than one version, and the “6.5 GAP 4S” head stamp on Hornady cases differentiates it from the rest. The RCBS dies I have are marked 6.5 RSAUM. Despite the different names, the cartridge originated as the 7mm SAUM case necked down with no other change, and it is more commonly referred to as 6.5 SAUM. Gross water capacity of the GA Precision case is 72.3 grains, or about 4.0 grains more than Hornady’s 6.5 PRC. Cases formed from Remington and Norma 7mm SAUM brass hold a bit less water. As other comparisons go, Hornady 6.5-284 cases hold 64.3 grains while 6.5 Remington Magnum cases made by Remington hold 70.2 grains. The old 6.5-06 case formed by necking down Federal .270 Winchester brass tops out at 66.9 grains, and .264 Winchester Magnum cases on my shelf hold 82.4 grains.

Several different chamber neck diameters are out there. With a .264-inch bullet seated in the 6.5 GAP 4S headstamped case, outside neck diameter is .292 inch. Outside-turning to .291 inch uniforms neck wall thickness. Necked down Norma and Remington 7mm SAUM cases are reduced to the same diameter. When installing a heavy, 26-inch 6.5 SAUM Shilen Select Match barrel on one of my switch-barrel target rifles, I went with a .295-inch chamber neck.