I found this board when I was looking for info on the big 30's (OK, maybe the mid 30's). I couldn't understand the draw to the 300RUM when it only gave a couple hundred feet over the WM with a 180gr bullet; I could get thet with a longer barrel. I was schooled by the more knowledgable mambers here that the bigger cases shouldn't be compared with the same weight bullet, but with the more efficient bullets weights for their capacity (apples-to-apples). If you want to shoot lighter bullets got with a 300WM or WSM. If you are going to burn the powder, in the big case you should push the bigger, more efficient bullets. Just my thoughts.
I agree with Jon A, With a 12 turn barrel have it made into a WSM and shoot the lighter bullets. It's kind of like vehicles; you don't need a semi to haul your groceries. It will work, but it sure is a waste of fuel (powder). There are better/smaller tools for that job.
On the other hand, you have the barrel and it will cost the same getting it put together; make a lazer out of it and have fun. Won't last as long but it will be a fun ride.
I'm having a 300RUM made right now and it will have a 9 turn barrel. I was looking for a 10 but the smith had a MUCH better 9 twist in the shop for the same cost so I went with that; same cost, , better quality, better turn around time, and it will stabilize the 200-220gr bullets I wanted to shoot.
If you want to make a 300RUM out of it GO FOR IT!!! But it probably won't be the best/most effective use of the barrel.
Genises 27-3: Now therefore take, I pray thee, thy weapons, thy quiver and thy bow, and go out to the field, and take me some venison...