I impulse bought a 4" fixed sight full lug barrel (new/never installed) for my currently 3" fixed sight Ruger GP100. My original thought was to have this new 4" barrel slab side milled and the under barrel lug ground off to be a half lug. After I started researching what it would take to properly fit the new barrel myself (lathe and mill work), I'm rethinking the project. Has anyone had any experience with a local (SE MI Metro area) gunsmith who might be able to do such a barrel swap at a reasonable price? I think I could handle the slab sides and underlug grinding and filing myself.