Looking to see if anyone out there has any loading data for this wildcat. The project was finished 10-12 years back before the introduction of the WSM and RUM cartridges. I just recently got the rifle from the gunsmith (I moved before it was finished). I will be using 300 gr. Sierra MK bullets. I figured I might as well test it out before I have it rechambered for some other hotrod 338 cal cartridge. Thanks.

Big Stick, what's the capacity of the case? It's bound to be nearly that of the Weatherby case, or somewhere between that of a RUM and Wby case. The powders should be slow enough that you can extrapolate. I've used everything from H-4831SC to H-870 for the 300 Mk's in my 338/378. Hopefully that'll give you a start.

Not sure. I don't have any fireformed brass yet. I do have 100 Norma cases ready for firefroming. It will be close to the 338/378 Weatherby. I knew I could use 338/378 loads to start with, just checking to see if anyone has any first hand experience with this cartridge. But thanks for your input.

What powder do the 300's like best in your 338/378 and what were your velocities for the better loads? I'm hoping for 3000 fps with a 300 gr. moly'd bullet. I do have a 40" barrel by the way. Think its doable?

I suggest you contact Darryl Cassel, I know he has pretty extensive knowledge of this round. He hangs out at http://precisionlongrangehunter.com/groupee these days.

Also, Dave King, who does post here every now and then but more often at http://longrangehunting.com/ubbthreads/ubbthreads.php?Cat=0 IIRC has used this round a fair amount.

They could get you pointed in the right direction.

Thanks Jon A. for the direction. I have since posted the same questions I posed here on both of those forums. Am looking forward to hearing something in the next few days.