For the .338 Lapua Magnum chambering a non-traditional 305 mm (1 in 12 inch) or 36.4 calibres right-hand twist rate was selected to optimise the rifle for firing 16.2 gram (250 grain) .338-calibre very-low-drag bullets. As of 2009 .338 Lapua Magnum barrels can also be supplied with a 254 mm (1 in 10 inch) or 30.3 calibres twist rate optimised to stabilise longer, heavier very-low-drag bullets like the Sierra HPBT MatchKing and Lapua Scenar .338-calibre 19.44 gram (300 grain) bullets. The traditional 254 mm (1 in 10 inch) has since become the standard twist rate for the .338 Lapua Magnum chambering. Due to the .338 Lapua Magnum cartridge dimensions it is a long TRG-41/TRG-42 bolt-action chambering.