CE Harris says
"125 grain plain based "small game/gallery" 900-1000 f.p.s., 5 grains of Bullseye or equivalent."
Equivalent = WW231, SR-7625, Green Dot, Red Dot or 700-X
These are good out to 50 yards and cheap to run. If you wanna go further I d suggest a heavier boolit.
If you do insist on trying to run these further. Then I d suggest 16gr of 2400.
Also .311 is probably going to be too small for the enfield.
Jeremy