I played around with a wildcat a few years ago where I necked up a .308 Winchester to .338. It was a pleasant gun to shoot (compared to a factory .338 Win.) and was very accurate. The bullets I tried (210 Nosler Partition and 225 gr. Hornady) didn't expand a whole bunch, but gave a lot of penetration. Speed was about 400 fps below the .338 Win Mag.