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Kroil is a penetrating oil not a solvent and should be fine to leave in the barrel indefinitely.
It should loosen any rust left in there too.
I wouldnt stress about it it will probably still shoot...

Jackangus could this orange you see down the muzzle be copper streaking from the bullets?
If so this is not uncommon and is not a problem untill it affects accuracy and then it is. A good copper...