Unless there's an obscure cartridge that I can't remember right now, I think you're referencing the same thing. A No 4 Mk1 is chambered in 303 British. There may be some headstamped Enfield though I've not seen any. What I've got here is just 303 and then date stamped. It was used in the Enfield series of rifles and I think in one of the belted machine guns --- again, poor memory.
I had a No 5 for several years and always bought 303 British ammo for it. Never a problem.
Hopefully, someone else will jump in here and either confirm or say "no, dummy....." with the right info.
I had a No 5 for several years and always bought 303 British ammo for it. Never a problem.
Hopefully, someone else will jump in here and either confirm or say "no, dummy....." with the right info.