April 3rd, 2012

Comparative Specs for Various 6XC Brass Sources

GS Arizona, a top small-bore and centerfire shooter, uses the 6XC cartridge in some long-range matches. He has tried a variety of different types of brass for this cartridge, including necked-up 22-250 brass and Norma 6XC brass from David Tubb’s (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
GS 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. The tester did not have a chance to measure the high-quality Lapua 22-250 brass introduced in 2010. NOTE: These differences in case capacity are large enough that you MUST adjust your load to the brass type.

Norma 6XC brass David Tubb

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).

We recommend sticking with the Norma 6XC brass. It is available from DavidTubb.com for a reasonable $69.00 per 100 cases. These days, that’s cheaper than many other types of premium imported cartridge brass.

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″ (with no-turn brass). 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 at least .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.

NOTE: The research for this story was conducted in 2010. Dimensions may have changed with more recent production, so you should double-check the case capacity of your own 22-250 or 6XC brass.

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