My best results for 300 gr TSXs was 70.5 gr of Norma 203B -basically full load with a hair of compression. (Book max was 71.5 gr of RL15)

I was going to do the same with the 250s - start low and work all the way to max load.

I loaded the 300 grs at 3.57" COL (Barnes recommended) and got the best results. Tried other lengths up to 3.629. Figured I'd go 3.57"; also 3.680" puts me at the top of the second pressure relief groove (whatever it's called). I use lee crimp dies. Lands on the 250 gr are WAYYYYYYYYYYYYYYYY out - about 1/5" of an inch from max magazine length.

A long jump works just fine. My .375 Wby likes COAL of 3.575" crimped at last groove best.

I checked capacities tonight at 3.575". 72 gr is max, maybe a hair compressed. 71 gr has just under 100%. estimating about 2,700 - 2,725 fps based on my 300 TSX results. I was hoping for a lot faster - like 2,900 fps. we'll see.

My .375 Wby didn't manage 3000 fps even with 235-grainers, FWIW. (IMR 4831 there.) I get 2825 with RL-15 and 78 grains with 250-grain TTSX. So,...

Tried RL15,IMR4320, H4895 maybe a few others and couldn't get what I consider acceptable accuracy. Got some IMR4451 and that finally got me under MOA.