The 338 KT is otherwise known as the 338 Keith -Thompson, co-designed by none other than Elmer Keith himself. It was designed around 4831 speed powder. There is an excellent write up on it by Ross Seyfried in Guns & Ammo in one of the issues in 1985 I believe. It is indeed the 378 Weatherby shortened by .25" and necked down to 338 caliber. An awesome long range cartridge truly ahead of its time and basically duplicates 338 Ultramag performance, a 250 gr bullet at around 3000 fps.