Clean it, a lot. The Micro-grooves are full of something, probably jacket fouling or lead (or both). Alternate scrubbing with a brass brush, and then just use patches with copper solvent (and a plastic jag not a brass one).

The other alternative is a badly damaged crown, but presumably the gunsmiths checked that. A .30-30 should be able to stabilize any off-the-shelf ammunition.

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MikeG