303s a weird one to start with, they were manufactured with a large assortment of barrel diameters. I assume you are just getting into reloading so no offence if this is to general an answer. When I first started, I always found cheap (.311)180gr as they where nearest of the factory rounds. I had a Jungle Carbine which shoot those things ban on every time. Later I bought a #4 Long branch with a very large bore around .316 so the .311 would keyhole, I had to cast to find any accuracy at all. Hope this helps you
