Safe to Shoot in a 7x57 Spanish Mauser M1916

[Ovidio]

I’d love to help, but I never used IMR powder.
If the rifle is a large ring, you can be pretty sure that it’ll be extremely sturdy, but still... I’m very scheptical when it comes to reloads that I didn’t personally assemble.
Did you try and look at the original IMR reloading data?