READ.
FYI - for .303 British, SAAMI specs are GO .064", NOGO .070", and FIELD .074". I own a NOGO gauge in .303 British and use some tape to bump it up 4 thousandths when a rifle closes on it.
Enfields have notoriously sloppy headspace dimensions. Always check them or have them checked by a qualified gunsmith before firing. If they are out of spec, you can have a case burst in the chamber. I'm checking out two for a buddy tomorrow. Not difficult - remove the extractor (simple) and don't force the bolt handle closed (finger pressure only!).