Lead bullets overpressure??? No way. Lead bullets offer less friction, start easier and generate lower initial starting pressures than a jacketed bullet .
The only reason they say do not shoot cast in polygonal rifling is due to poor accuracy with the softer bullets. Polygonal rifling has rounded lands and soft cast bullets don't grip the lands like a jacketed would and therefore tend to not stabilize properly. At 10 yds you won't notice this, but as range increases you will. I shoot cast out of a G19 and they shoot fine, but I cast with a hard alloy beefed up with linotype for hardness.
Polygonal rifling was developed for one reason. That was to extend barrel service life.
Anyone who would let a barrel lead up to the point where it restricted enough to cause a safety issue deserves to blow himself up. Even in the worst case scenario, I'll bet you you wouldn't blow up a serviceable gun from barrel leading. Think about what happens when you fire a shotgun slug through a full choke. The same thing would happen to your pistol bullet. It would swage down to the ID of the bore just like that way oversized shotgun slug does.