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yep , older hunting rifles sometimes "wear" at the muzzle not from any wear as such but from rust and cleaning as that is where the water gets in.

I could send you a few hand loads of a recipe...

Yea that.
you won't lose Bugger all velocity from an inch.
when you say it looks worn can you see better rifleing down the tube? how old is it and how many rounds been down the tube?
ss or blue ?...