Full house/heavy loads in an Enfield, even if the headspace is good, are a sure recipe for short brass life (sometimes, VERY short). I load mine down to around 2200-ish FPS with a 180 grain bullet and a slow-ish powder (H4350 comes to mind as being a great idea; though I do mine with Win760, just because I have a pile of it already on-hand), and I routinely get 4 or 5 firings instead of 2 or 3.
Not that I shoot my 303's much anymore since I discovered that with slightly toned down loads and a neck sizing die, I can apparently reload 308 Winchester brass for a modern rifle indefinitely (I haven't worn any out yet, and I shoot quite a bit!)
So anyway -- I revise my advise above; get you something like H4350, and load it kind of mild (46-ish grains with 180 grain bullets ought to be about right, according to QuickLoad -- though as with all things reloading, field observations should take precidence over anything QuickLoad or some book tells us!)