Don't recall the specifics but PO Ackley did a bunch of tinkering with the .303...or somebody did during his era. I've got one of his books hiding somewhere, will see what I can find for you. One I have recollection of was a .224 and another was for the .257 bore.
FWIW, you can probably do anything with the .303 that you can do with the .30-06, bigger or smaller. I'd also think that if you're using an Enfield for the platform you might want to take a close look at feed geometry before leaping off the cliff.
