.338 Cheytac?

There were a couple of dueling cartridges when they were in their hay-day, the 338 SnipeTac and the 338 Allen Mag. Both are very similar cases and they're both a 375CT Improved, necked down to 338. Both built on the Stiller TAC408 action, both DBM, both posted about the same performance numbers.

A friend has a bad to the bone 338 Snipetac with a 32" Proof Straight 1.250" and it pushes the 300 grainer along at >3300fps, all under 16lbs scoped and ready to roll. The downside is that he waited ~8 years for that rifle by the time it was all said and done, and the gun had to go back a couple times for issues. He's said over and over how giant of a pain in the ass the whole ordeal was and he wouldn't do it again. I think Viers has shuttered the business since, on the back of some accusations of dodgy business.

Kirby Allen is still churning out the Allen Mag though. It's a pretty long wait, I waiting just shy of 2 years for a 338 Allen Xpress from him, but he's a good gunsmith and everything I've seen from him is top notch. Link to his wildcats if you're curious. http://apsrifles.com/Allen_Magnum_Wildcats.html