Nick,the 275 H&H was introduced in 1911/12 and were the first 7mm.mags. but although a fair no. of American custom rifles were made for this round no factory rifles were made.The belted version known in the U.S. as the 275 H&H MAG.was loaded by the Western Cartridge Co.until 1939.It was developed by F.W.Jones as an improvement of the 280 Ross.Eley and Kynoch loaded bullets of 105,140,143,150,160 and 180 grains.The 275H&H Mag.is similar to the 7mm.Rem.mag.