I have a Ruger in 300 WM that has somwhere between 5/8" and 3/4" of free bore. It took me a really long time to find something that would shoot in it and now I can shoot groups in the 3/8" range and on regularly shoot in the 3/4" range.

May take some shooting to figure it out. If you have the money I would talk to a smith to remove some of that freebore but you'd be better off putting a new barrel on it.

I was pretty upset when I measured my Ruger. I didn't do it until after a I found a load. I kind of learned to reload with that Ruger. So some of it could have been bad reloading practices.

Tom