The .338 Norma Magnum is a caliber initially made in the U.S. as a wildcat cartridge and is now a precision rifle cartridge manufactured by Norma.
The .338 Norma Magnum was originally designed by American sport shooter Jimmie Sloan as a sport shooting wildcat cartridge with help from David Kiff, the founder of Pacific Tool and Gauge, who manufactured the reamers and headspace gauges.
Barrels for the cartridge were supplied by Saturn Rifle Barrel Company. Various twist rates were tested with 5R rifling. The cartridge was deisgned to optimize shooting the Sierra HPBT MatchKing bullet from actions and magazines that did not have the length to handle cartridges exceeding 91.44 millimeters (3.60 inches) in overall length.
Later on, the design was purchased by the Swedish ammunition manufacturer, Norma. On May 26th, 2010, the .338 Norma Magnum received its C.I.P. certification, therefore becoming an officially registered and sanctioned rifle cartridge.
Prior to its C.I.P. certification, the .338 Norma Magnum had a shorter overall length when compared to the .338 Lapua Magnum.
It loaded with .338 caliber, 19.44 g (300 gr) Sierra HPBT projectiles that would be less deeply-seated compared to the .338 Lapua Magnum when both cartridges are loaded to 91.44mm (3.681 in) overall length.
For this, the .338 Norma Magnum uses a shorter case, which is based on the .416 Rigby, with less taper and a slightly sharper shoulder angle with a slightly longer neck. This results in about 6.5% less case capacity.
However, the overall lengths between both it and the .338 Lapua Magnum are currently determined, as of 2013, at 93.50mm (3.681 in) by C.I.P. rulings for them.