Exploding Gun Myths
Myth: If your revolver or pistol barrel is leaded up from cast bullet, just shoot some jacketed bullets down it to clean the lead out.
False: I had a .357 S&W come into my shop. The customer said it was shooting all over the place. He said it was probably the fault of the lead bullets he had been shooting. That was the clue I was looking for. I asked him,"Say did you by chance shoot a few jacketed bullets through the gun to clean out the lead?"
"Yeah I did, a couple cylinders full, but it didn't do any good" He said.
"You are right," I answered" "But it did do everything bad." "The good news is your revolver can be fixed as good as new." "The bad news is it is going to cost you a pretty piece of change." "You cracked the forcing cone and the barrel for about 3/4".
"HUH? he said, "It must have been a bad barrel" "All I have shot in it was lead target loads."
"And a couple of cylinders full of jacketed rounds you said", mentioned Sarge. "Yeah but it didn't make it shoot any better" I said, "Remember"? "Yes, but it did crack your forcing cone and barrel", Sarge came back.
Here is what happened: When the lead from the soft lead target bullets filled up the rifling, it also was deposited on the forcing cone by the hot burning powder gas. No lead cast bullets have clean perfect bases. There are little fins of lead sticking out on the base and on every lube groove. The hot gas melt these and carry it forward until it hits the forcing cone and builds up on it. The forcing cone and the barrel next to it is slowly filled with deposits of lead which builds up making them close down smaller and smaller. Then when a jacketed bullet is shot, the harder non-compressable (relatively speaking) bullet at 18,500 PSI forces the deposited lead into the tapered forcing cone until reaches the cylindracal area of the barrel where it exerts outward pressure on the barrel/forcing cone junction. At this point the peak pressure is much higher because of the restriction of the leaded up barrel. Something has to give and the forcing cone and barrel does.
So don't believe all old advice from old shooters.
PS the myth grew out of the practice of using a cast bullet with a gas check on it. The gas check had a sharp edge on it that did make a very good scoop shovel to scrape out the lead with out over riding it.