I fell into this rifle as a gift.
This is a 338 Win Mag expanded to 375, same case length.
I can find all kind of loads for 260 to 300 grain jacketed bullets at 2600 fps+.
Can anyone help me with some CB data at reduced loads up and down the scale?
Thanks - Lew

Lewis. Congratulations on getting a rifle in a fine cartridge. I've only done one cast bullet load in mine, built on a tang safety Ruger 77. It's the RCBS #37-250-FN with 49.0 gr. of IMR-4895. It has a couple of drawbacks, the first being that the base of the bullet with the gas check is well below the neck of the case. I don't like that situation at all. Accuracy was only fair at best. I'm thunking along the lines of a custom mold of maybe 230 gr. or so with a wide flat nose. Might make a good deer load.
Lyman has a bullet that is supposed to go 250 gr., but it's so similar to my RCBS mold that I think it will end up being around 270 gr. again and would most likely still be way too long.
If you seat the bullet so as to have the base just even with the back of the neck, then it will jam into the rifling and be pushed deeper into the case.
I ran into a similar situation with a 6.5 Mannlicher and a cast bullet years ago where I had what appeared to be an overload. As near as I can figure out, the gas check came off and then when I shot the gun, it lodges just long enough back into the neck to cause the pressure to rise drastically. Load was a near full power load, so a double charge would have been impossible.
t one time, Lyman made 16 different bullets for .375 caliber, but I believe #375449 is probably the only one still in inventory. If you can find a copy of the Lyman cast lead manual (second edition) there is a list with photos of the different .375 bullets. At least it'll give you an idea of what to look for in used molds. I've found a few in weird oddball shapes for 30 caliber nosing around gunshows and gunshops.
Good luck.
Paul B.