where are you finding these horrible shooting mosin nagants even the worse bore ive ever seen was not that badPlease be aware that you may be looking at a gun that shoots 12MOA both before and after all your hard work. It may shoot 6 MOA after your work. That is very good for a gun that is expected to take deer at 100yds.
I was only suggesting you might get more personal satisfaction from a rifle capable of much greater accuracy.
Good luck in your endeavor