You could use the valve grinding compound on cast bullets - fire- lapping.
I did that with my Model 71 Mauser with a pitted bore. Came out quite shiny, but did enlarge it .001". The grooves were good, so I only put the compound on the bore riding nose of the bullets. I fired about 40 of them - squib loads, low vel.
Trail Boss would do well in this application - about a 70% load.