Black bores. Hum? What is the cause of black bores in some rifles? I have a 1903 springfield with a black or very dark bore. The barrel on it was refitted in 1944. Lots of lands and groves and it shoots ok. So why the black bore?

I would guess that it's a combination of powder fouling and tarnished copper. Does it come out when you clean it? If you scrub it with a powder solvent do you see green or copper fouling in the bore.

A lot of the older rifles fired ammunition loaded with cordite (at least the english ones). Cordite burned very hot and caused the barrels to become black, also called cordite burn! I have seen many rifles in this condition.

Could it be barrel blue?

cordite smells so hot....

Some ex-mil ammunition (if that's what your using) has a tar like sealer on the projectiles that can leave some pretty stubborn black fouling.
Cheers...
Con