Geo T said:
I managed a gun store for 5 years and there are two things that will remove both external rust and internal. They are P B-Blaster available at Auto Zone and Tractor Supply here in Texas. The other necessary item is Time. Given enough time the PB will loosen the rust. It may take three or foue days but wet the bore a couple of times a day. About day two use 0000 steel wool apply it. Use several strokes and you will see the rust melt away slowly and you will do so without doing further damage to the bore.
At that point you can see if polishing is required. JB bore lapping paste will do a good job. It has been my experience if it needs more aggressive compond like valve grinding paste it may well be new barrel time! Good luck and let me know how it goes.
Geo. T.
Thanks for all the advice. There is light pitting that I can see but I figure if I stick with PRB's that won't be much of an an issue. I have been using PB Blaster with the 4/0 steel wool wrapped around a .45 bronze bore brush to do the initial cleaning along with an application of J&B bore paste.
Next was warm soapy water which removed a lot of crud from the powder charge left in the barrel. Patches are coming out white now, I just want to be sure I get all the rust. Push come to shove, I could always rebarrel it with a Green Mountain 50 cal barrel. I'll hold off on any rebuild decisions until after I shoot it some.
Tom