First off, you have yourself a real shooter there!
Give it a try with some cast bullets. I have a Model 94 in .32 Special that has some light pitting yet it shoots cast bullets well. Like yours, it shoots jacketed bullets very well.
Try a 170 cast bullet sized .322" or .323". Seeing your bore slugs at .3210" you want to have your cast bullets .001" to .002" oversized, at least I have had my best accuracy with oversized cast bullets. If I use a bullet that is sized to bore diameter I usually end up with very poor accuracy.
I rarely use gas checked bullets. I feel that a cast bullet that is properly sized .001" to .002" over bore diameter, along with the proper hardness, does not lead at the velocities I load them to. At higher velocities (over 1600 fps) they may lead but I like to keep the speed around 1600 or less.