You don't want to stick anything abrasive in there especially dremel powered. The correct fix is a cleanup pass with a fresh finishing reamer lubed with some high sulfer cutting oil to true up the charge hole to SAMMI specifications. Done by hand BTW
This is a pretty common issue with mass produced rimfire revolvers. Worn tooling can result in slightly undersized chargeholes. Any defect in the tooling will be mirrored in the wall of the chargehole too with the same end result... sticky. Poor chip control when reaming can also lend to defects in the chargehole wall.
Chargeholes should not need any polishing after a proper cleanup pass with a good sharp reamer.
Do
not mess with the cylinder throats, you can quickly ruin accuracy. Throats have no bearing on the brass, they serve simply to guide/align the bullet with and into the forcing cone.
Cheers
Bill