@ pink : Best way to find out is by forcing a soft lead bullet full length through the barrel.
This will give you the minimum diameter of your rifling.
Then, take another and force it in roughly one inch....then take a dowel and gently tap it back out.
This will give you your most likely area of wear, and where most of us get barrels that are "shot out"
In the event either is significantly out of spec, you are not out of luck ! : If your full length pushed lead still contains significant rifling, brad at MBC will be happy to ( I hope he's not swearing at me for saying so) custom size within reason bullets of a larger diameter for you to use.
If you havent a few soft lead .309-.311 bullets to use, PM me your address and I will happily send you a few.
Hope this helps !