Hello, Bad Boy, you'll find--I'm sure--plenty of fans of the .303 on this board. Just the fact that Saint W.D.M. Bell used it extensively on elephant earns it a privileged spot in the Great African Cartridges Hall of Fame--plus, the fact that it has been the British Empire's military cartridge for 80 years makes it a staple from Canada to Australia and to South Africa and the rest of Albion's former colonies in the Dark Continent.
I myself am preparing to go on a safari in June, and one of two rifles I'm taking is precisely a .303.
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Due to the ammo and components shortage, my choice in bullets is limited to Prvi Partizan 174gr boat tail soft points, which give more than satisfactory hunting accuracy in this rifle. This Watson Bros Martini is an absolute tack-driver with 180gr Federal Power-Shok, although I only have a handful of rounds left of this brand and it's impossible to find more. These are all .311" diameter. I wish Hornady's .312" offerings were available--especially the 174gr round nose InterLock--but trying to find them has been a fool's errand.
Of course, what I really wish to take are the splendid 215-grain bullets that made this caliber a killer of any game on Earth in the hands of the likes of Bell. As far as I know, only Woodleigh and Hawk make them--the first being the victim of a November, 2011, fire that has placed production on hold, the latter so overstretched as to be backordered for over 8 months.
I'm glad every time I see a new .303 initiate. This caliber truly has it all. By the way, since your rifle has already been radically altered from its original military configuration, you may want to consider outfitting it with a new barrel. It's widely available for the N. 2 Mk. IV and for a few hundred dollars you can have it installed and headspaced. The problem with many of the existing barrels on British service rifles is that their throats are more or less shot out because of the use of Cordite, which has a very high nitrocellulose (=explosive) content. This is why you're limited to a certain accuracy ceiling, no matter how perfect your handloads. With a new barrel, you can truly explore all the potential of this wonderful (and wonderfully-historical cartridge).