February 2nd, 2012

Mid-Sized 6mm Cartridges — Great Accuracy & More Zip than 6BR

Many precision-oriented shooters are discovering that the “middle ground” in cartridge size is optimal for the 100gr to 115gr match bullets. With a mid-sized cartridge, you can run these pills faster than a 6BR or Dasher, without giving up much, if any, accuracy to a 6BR or BR Improved. The most accurate 600-yard rifle at this Editor’s local club is a 6-6.5×47. It can shoot as tight as a 6BR past 300 yards, plus it offers better ballistics, pushing 105 Bergers at 3140 fps.

If you’re considering a mid-sized 6mm cartridge for your next rifle, you’re probably wondering WHICH mid-size 6mm cartridge is best. We are often asked “what’s the difference between the 6×47 Swiss Match, the 6XC, and the 6.5×47 Lapua necked down to 6mm?” All three cartridges have 30° shoulders and fit a .308-sized boltface. However, alone among the three, the 6mm-6.5×47 has a small primer pocket and small flash hole. The 6×47 Swiss Match (made by RUAG), and the 6XC (produced by Norma), have a large primer pocket and large flash hole, just like a .308 Winchester.

Forum member DesertLefty has provided a line-up photo, with 6mmBR and .260 Rem cases provided for comparison. As you can see, the three mid-sized cases (6x47SM, 6.5×47 Lapua, and 6XC) are very similar. The Swiss Match has the longest neck, while the 6XC enjoys the highest capacity. But performance is very similar among the three cartridges (with the 6.5×47 necked down to 6mm). The same powders, (particularly H4350, Reloder 17, and IMR 4007SSC) work well in the 6×47 SM, the 6XC, and the 6-6.5×47 Lapua. The parent 6.5×47 Lapua case is rated at 63090 psi, while the new CIP rating for the 6XC is 63844 psi (4400 BAR). Both the necked-down Lapua brass and the Norma-brand 6XC brass can hold stout loads. Though the 6mm-6.5×47 has slightly less powder capacity than the 6XC, max velocities with 105-108gr bullets are quite similar. However, you should not substitute loads from the 6XC directly to the 6mm-6.5×47 or vice-versa. Because of the different case capacities and primer sizes, you should work up loads separately for each cartridge.

6mm Cartridge Comparison

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