I have several milsurp rifles - my Krag one of them - with dark and worn bores. I shoot cast bullets in them with great success. The key is to slug the bore and determine the best bullet size for your rifle. Typically, most find good success with bullets sized at or 0.001 over throat diameter. Also check the muzzle crown with a loop or magnifying glass. Even small imperfections can grossly affect accuracy. You are doing the right thing - clean 'er up and give it a try!