I've made a lot of custom 338/378 KT's on 602 actions and another unmentionably ugly action (no, not a BU-21). I kept calling W'by about coming out with a 338/378 but they seemed disinterested. They then came out with the 300/378 (for some reason) and the 338/378 soon followed. I REALLY like the 338/378. About the same ballistics with a 250 gr bullet as the 300 with a 180 Gr bullet. Current powders available to us are better than the W'by powders and we can reload better than their factory ballistics. Just don't use Hornady bullets with these higher velocities. Liquid plasma comes out the barrels instead of bullets. I have loaded 250 Gr bullets to over 3450 FPS but over 3250 FPS the barrel life is destroyed quickly. With the removeable W'by muzzlebrake, recoil is mild.

By the way, although the Japanese guns are not as collectable as the German guns, the triggers are higher quality. They also have a 5/16" pin through the wrist which makes the weakly designed W'by wrist much stronger (except when W'by forgets to add the pin). I think W'by stared adding the pin on larger calibers first in the latter 60's but cannot find out for sure. They added side pins glassed in behind the recoil lug about the same time for good reason.