Today trying out a new load for my 375 Ruger Alaskan.

Speer 285gr.Grand Slam.
Varget-71.0
Case-Horn 1X fired
Pri.F215
O.A.L 3.300
Vel-2600fps
Air Temp.100deg.

Everything looked great, accurate. Re-adjusted the scope for zero. About 6 or 7th round on final sight-in (3 shot groups then cool down)
And Whooop's!!! Whoa.. Ruptured case at the web.

Now this isn't a max load..... Is it?? Faulty case??

Opinions needed..

I'd call it a case issue. QL calls the pressure in the 57,000 range.

Headspace?

No good answer for you, but I can share an alternative load. I have been shooting 300 grain Barnes TSX in front of 70 grains of RL15 and a F215M primer. Get one hole groups at 50 and 100 yards in my ugly Ruger Guide Gun. Velocity is right at 2400 fps.

Yep, moderate load.
Check the headspace on the rifle?