6XC Brass Dimensions and Capacities
German Salazar, a top small-bore and centerfire shooter, uses the 6XC cartridge for his long-range matches. German has tried a variety of different types of brass for this cartridge, including necked-up 22-250 brass and 6XC brass from Norma and David Tubb (Superior Shooting Systems). German’s measurements reveal significant differences in water capacity, as well as neck-wall thickness.
6XC Source Brass Dimensions
Case Capacity and Pressure Issues
German has noted significant variances in capacity among the different “flavors” of brass. Norma-headstamp 6XC brass has 49.3 grains of H20 capacity, while Norma 22-250 brass holds only 47.8 grains of H20. Third-generation Tubb-brand 6XC brass is somewhere in the middle, with 48.6 grains of capacity. NOTE: These differences in case capacity are large enough that you MUST adjust your load to the brass type. A safe load in Norma 6XC brass could be WAY over-pressure in necked-up Norma or Remington 22-250 brass.
We ran a 6XC QuickLOAD simulation with 115gr bullets and H4350 powder. QuickLOAD predicted that the observed difference in case capacity can result in pressure differentials as much as 4,500 psi! In other words, if you switch from Norma 6XC brass to a lesser-capacity brass type, your pressures could rise 4,500 psi (using H4350 and 115gr bullets).
Neck Thickness and Chambering Issues
German noted that the different types of available brass varied quite a bit in neck-wall thickness — from 0.0121″ (Norma 22-250) to 0.0140″ (Tubb 3rd Gen). Consequently the diameter of loaded rounds also varied. Depending on the brass you chose, your loaded rounds could be 0.267″ at the neck or 0.271″. That’s a huge difference and it’s something you need to take into account when you have your chamber cut for a barrel. For a cross-the-course rifle, you might want a chamber with .003″ total clearance over a loaded round. Obviously, to achieve that clearance, you’ll need to set chamber dimensions base on your preferred type of brass.