For my 375 H&H I am loading a reduced-load for plinking and possibly very close hunting. Open sights.
235 gr Speer with Somchem 335 powder.
https://www.somchemreload.com/search?c=8&f=127
Start load is 64.7 gr.
Is 60 gr too low?
If not, is a filler of tissue paper (I have no dacron) necessary?
If so, is a .75" square adequate?
Advice will be appreciated.

No knowledge of this powder.

But, 60 grains is 10% less than starting load, so should not be a problem.

I think you won’t need to use a filler for that much powder.

For reduced loads we usually use pistol or shotgun powder.

Works best.