Solvent, toothbrush, effort. Wear gloves and do it outdoors. Back in the day we’d take The M14’s or of the stock and stick them in a 50 gal drum of gasoline and stir. Pretty sure this is not actually a good idea.
I bought an 03 Springfield once that looked like someone took a grease gun and filled the bore from one end to the other…… took forever…. Lots of patches and solvent… my guess is the rifle was never shot once it was rebarreled. Bore looked brand new.
If you know somebody with a cerakote or powder coat oven ask them if you can cook it for several hours. just make sure it drains into a metal bowl. Or if you live someplace hot let it bake in the sun. That's how I used to do my Nagants and Mausers when I was collecting them.
I used to stick garand stocks in the back of my car at work and let the warm up on a hot day. Metal took a good scrubbing with hoppes and a paper towel… Or soak the metal parts in a large tub with diesel fuel. Worked well
View US 3rd Marine Division armorers repairing small arms vintage historic HD stock video footage in Iwo Jima, 1945. Buy HD video and archival still photo images of clip number 65675064084.