I have pushed as much as 40 gr FFF to see what it could knock down in my steel silouette plates. My best accuaracy is like the other guys, 25-30 gr. I use the .310 cast rb with .010 patch from what's left of my Ox Yoke in .30 to .40 cal
I am not sure if the 40 gr would be enough to get a deer, but it don't matter cause State Law is .40 cal or bigger anyway.
Good enough for any smaller game you bet!