Abrasive bullets, interesting concept. I'll admit the idea of using abrasives makes me real nervous, but its worth more investigationI disagree that lapping could cause a problem. It's really a low impact process. Most barrels are have a choke at the muzzle. Basically you take something like a jag on the end of a cleaning rod, run it up to the end of the barrel. Wrap the end of the rod with something to prevent the casting material (cerrosafe) to flow past. This cast will be your lap. Use very fine abrasive i.e. valve grinding compound to coat your lap. Run it threw your barrel as if you were cleaning it. Go slow and check your progress.
David Tubb developed a system of abrasive bullets to "fire" lap your barrel. I mean, Tubb should know what he's doing but, that process seems really high impact.