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Cartridge dimensions Of the 338 LAPUA

Extremely thick-walled brass results in a 7.40 ml (114 grains H₂O) cartridge case capacity for the .338 Lapua Magnum. The exterior shape of the case was designed to promote reliable feeding and extraction in bolt action, semi-automatic, and automatic firearms alike, under extreme conditions.

 

.338 Lapua Magnum maximum C.I.P. cartridge dimensions. All sizes in millimeters (mm).

Americans would define the shoulder angle at alpha/2 ≈ 20 degrees. The common rifling twist rate for this cartridge is 254 mm (1 in 10 in), 6 grooves, Ø lands = 8.38 mm, Ø grooves = 8.58 mm, land width = 2.79 mm and the primer type is large rifle magnum.

According to the official C.I.P. (Commission Internationale Permanente pour l’Epreuve des Armes à Feu Portatives) decisions and tables edition 2007 the .338 Lapua Magnum case can handle up to 420.00 MPa (60,916 psi) P_max piezo pressure. This now prevails over the C.I.P. decisions and tables edition 2003, that rated the .338 Lapua Magnum at 470.00 MPa (68,168 psi) P_max maximum piezo pressur.^] The 470.00 MPa (68,168 psi) P_max maximum piezo pressure C.I.P. ruling for the .300 Lapua Magnum cartridge, which is based on the same case, was at the time not accordingly changed. In C.I.P. regulated countries every rifle cartridge combo has to be proofed at 125% of the prevailing maximum C.I.P. pressure to certify for sale to consumers. This means that .338 Lapua Magnum chambered arms in C.I.P. regulated countries are currently (2013) proof tested at 525.00 MPa (76,145 psi) PE piezo pressure.

Lapua has been ambivalent on the maximum piezo pressure of this cartridge. In the article ‘From an American dream to a Finnish success story’^[67] by Janne Pohjoispää Lapua propagates the C.I.P. 2007 ruling of 420.00 MPa (60,916 psi) maximum piezo pressure. To further complicate matters the mentioned 56,000 CUP C.I.P. copper crusher pressure in this article would translate in ≈ 447.50 MPa (64,904 psi) C.I.P. piezo pressure according to a study on the conversion from CUP to PSI for rifle cartridges by Denton Bramwell.^[68] The C.I.P. 2003 ruling of 470.00 MPa (68,168 psi) piezo pressure is corroborated by Lapua Australia in the ‘History and development of the .338 Lapua Magnum’ article by Alan C. Paulson.^[69] A reverse engineering simulation with QuickLOAD internal ballistic software predicted that Lapua load their factory .338 Lapua Magnum ammunition at ≈ 420.00 MPa (60,916 psi) piezo pressure as Alan C. Paulson asserts in his article.

The large boltface combined with the maximum pressure means that the .338 Lapua Magnum should only be chambered in rifles that are capable of handling such large high pressure cartridges and thus high bolt thrust safely. Chambering such powerful super magnum cartridges in rifles intended for normal magnum rifle cartridges and using high pressure loads can cause serious or fatal injury to the shooter and bystanders.

The American .338-378 Weatherby Magnum cartridge introduced in 1998 and the American .338 Remington Ultra Magnum (.338 RUM) cartridge introduced in 2000 are probably the closest ballistic twins of the .338 Lapua Magnum commercially available as of 2007. The .338-378 Weatherby Magnum is however a belted cartridge and the .338 Remington Ultra Magnum is a rebated rim cartridge.

The American SAAMI (Sporting Arms and Ammunition Manufacturers’ Institute) has no normal voluntary guidelines for the .338 Lapua Magnum. On 14 January 2013 it opted to use the metric C.I.P. rulings and add some dimensions that have no C.I.P. analog.