i have 2 26 inch barrels in 243 and 243 ai for my grandson they fit an encore frame.he shoots 105 berger vld in both with a 1 in 9 twist no problem.as far as the chamber a good gunsmith can bore the throat out a little.i just had a 280 ai done no special reemer.your mag will give you problems...
why waste the money you have a cal. that will do anything the 300 win mag will do and also has alot less kick.i have a rem 700 sendero in 300 wsm and i love it.also had 2 300 win mags and got rid of both