You can look at the .303 British cartridge, and compare it to a .308 Winchester. That's about as close as your going to get. That being said, you can use the .303 on anything you feel comfortable using a .308 on. Hornady makes a decent bullet in the 150 class. Interestingly enough, I called Nosler a few years back and inquired why they don't buile a .311 or .312 dia. bullet. They told my they can't keep up with what they have now, and who would really want a premium bullet in such an obscure caliber! This from the same guy's who offer a Ballistic tip in .375! You have to figure they would sell far more .303 Partitions as opposed to .375 Ballistic tip's, no? If you could find a readily available premium bullet, I would reign the Lee Enfeild as the supreme rifle. Think about it. If you were to manufacture the same rifle today, with all that machining and fitting, it would cost a fortune.
http://www.marstar.ca/gf-AIA/M10-N4.shtm It's close, but not quite. The rifles are extremely durable, quite accurate and totaly dependable. If I could only have one rifle, this would probably be it. Spare parts are a breeze, and there have been some mighty fine sporters made. Ever see the movie the Ghost and the Darkness? My best friend only really owns one hunting rifle. It's a .303 Lee Enfeild that we monkyed around with. We dropped it in a synthetic stock, and mounted a Bushnell Trophy on it. I then worked up a nice handload that litteraly cloverleafed three 150 grain hornady's at 100 yards. I used his rifle on my first day out this fall. And I'll tell you, it just felt right carrying it. But i told him, after hunting with it, to fill the stock with foam. It sounds like a drum in the sticks.
And this one is mine. I bought it as a back-up rifle/truckgun/beater. But it lends itself so well as a hunting rifle, I may do somthing with her.
Good luck with your collection. And take one or two afeild. It kind of throws you back in history.