Dwayne, there's a big difference between the 340 WBY and what the OP asked. He may decide that is what he's ultimately looking for, but it was my impression that he's wanting to re-chamber a 338 win mag and neck up a 300 H&H. Necking up a 300 H&H is not a 340 wby. and one can not simply re chamber a 338 win mag to make this happen. Too much taper on the H&H case. Dimensions and taper of the H&H makes for a not so likely endeavor....Like Kute has already mentioned, OKH developed a cartridge in the 40's. It used the .333 bullets instead of the .338 bullets of today. It was a 300 H&H necked up to a .333 cal and was made obsolete after the introduction of the 338 win mag in 1958. If you look at the dimensions of the H&H cartridge and compare it to the 338 win mag, you'll notice that the case diameter is too small near the shoulder on the H&H round. Thus, you can not simply re-chamber a 338 win mag while using a necked up H&H cartridge. The chamber would be too sloppy to allow for this and would split the case at a minimum or even blow the gun up. Hope this makes sense..
