Firecracking can be smoothed up with lapping bullets. Get a full-length neck bushing die and partial-size the brass, leaving the shoulder where it is fireformed to the chamber and a little bit of unsized brass at the base of the neck. Select a bushing which gives just enough tension to hold the biggest bullet that will fit into the throat. Use a universal expander to slightly bell the case mouth, and don't crimp (or only use enough crimp to make sure the cartridges will go in the chamber without scraping the neck too hard).
For even better results, turn the necks for uniformity after firing, just take enough off the high spots to get under .0002-3" thickness variance. Use Forster Benchrest seating die to reduce cartridge runout, though with oversized cast bullets the neck portion of the sliding sleeve will need to be enlarged slightly.