The L4 seems to have more recoil impulse when fired semi , the 303 is just smoooooth.
Its easier to find or load 7.62 and most of the 303 surplus is drying up or decades old.
I have several hundred rounds of MKVII 303 that is just a tad short of cycling my gun. Experimenting adding a full heavy crimp to bump up the pressure / impulse a bit.
Pulling the bullet and reloading with modern propellant does work 100%.