Well Ruger produces their Number 1 single shot in .303 British but that's not why it's so popular. After the war in the early 50s, they used to sell surplus Lee Enfields at deparment stores, brand new in the grease for $10. You could get a "sporterized" one for $15. Everybody and their uncle bought a .303. Every camp has one. It's what our guys used in the wars. They work great on moose, deer and black bear but aren't too handsome to look at. I think that the .30-06 is probably the most popular deer hunting cartridge in this neck of the woods, although it's not my first choice. The .30-06 is a great cartridge, I just find it boring because everyone has one. Now the .35 Whelen or 9.3 x 62 on the other hand...those are a little more interesting.
