I bought a .54 GPR used last fall at a good price. Supposedly was fired twice. The barrel was rough inside with tool marks. About 200 strokes with JB Bore Paste smeared over scotch brite pad and she was smooth. Went from 8" group at 50 yds to 1" using 70 gr. ffg and .530 roundball. I presume it was tearing patches before the polishing. Works great now, and I will keep it. Only other complaint I had was the buttplate being sharp along the lower edge, also an easy fix.
