What a great thread, and group! But you've instigated this new guy on your block. I have strong thoughts about cast bullets and real or mythical bore leading, after a bit over 61 years of shooting and 50 years of reloading and bullet making, cast and jacketed. During that time I've probably made just about every mistake that can be made, but I still have all my fingers and original body parts. I hope those mistakes have taught me how not to make more...or at least not as many.
Bmcgilvray has it pretty much right on all counts, as do some others here.
You don't pound lead into a bore by shooting jacketed bullets through it. That doesn't happen, with one exception. If there are deep pits, that's where the lead stays, unless removed with a brush or chemicals. But that's a losing battle, because lead from the next cast bullet will be deposited in the pits again immediately, even with correct alloy, lube, and velocity. You need a new bore, or stick with jacketed bullets in that gun.
A highly polished bore does not easily attract lead deposits in the first place, even if your cast bullet alloy is a bit soft and the velocity above the recommended limits. But a bore made with a bad reamer and cutter will attract lead, even when you are doing everything right. Those who have tried some of Numrich's barrels know about this.
Anybody ever ponder just what a gas check is for? It prevents hot pressurized gas from melting lead alloy from the base of the bullet and sort of soldering it to the bore at the higher velocities. But its secondary job is cleaning from the bore any lead which even that bullet, or a previous one, may have already deposited, despite being properly lubricated.
Does it work? There's no need to "wonder". I've examined hundreds and hundreds of recovered gas checks, in .30, .44, .45, and .357. Every one was plated evenly with at least a thin, fused coating of lead where it contacted the bore, but not on the bases.
S&W does a fine job of finishing its modern bores. A well designed gas check, made of the right gilding metal alloy, crimped onto a cast lead bullet of the Lyman #2 alloy equivalent, used even with good quality home made non-Alox lubes, will not lead a typical Smith bore up to at least 1500 feet per second, maybe higher. If you do get leading in that range, one of the controllable factors is not right.
Another consideration is that copper colored gas checks, and bullet jackets, contain all, or a lot of, copper. Few things bond as well as clean copper and lead/tin alloy solder, if you heat them together, which happens inside a gun barrel. We take advantage of this by pushing a jacketed bullet through a somewhat leaded bore. The thin lead deposits are sandwiched between the steel bore and the copper jacket, under great heat, pressure, and friction. The copper has a much higher coefficient of friction than the steel, and the lead alloy fuses to it more easily than to bore steel. Then with lead bullets, we try to use the right bullet lube and an alloy which hopefully ensures the worst possible "soldering job" on bore steel. Those of you who have done some electrical or plumbing soldering understand the dynamics of this.
There are a million ways to get leading, even in a smoothly polished bore, at velocities as low as 600 - 700 fps. That's airgun speed. Just use the wrong lube or soft alloy, or have a roughly bored barrel. And there are other factors.
During five decades of reloading, I have never before heard that the shooting of jacketed bullets in a moderately (not heavily) leaded bore is a bad idea, or that it is not a quick, safe, and effective way to remove such deposits. Lyman and just about everybody else has long recommended it.
Those who make .22 conversion kits for AR-15s and other gas operated rifles, such as the AK family, recommend that after firing 500 rounds or so of lead .22 LR bullets, you should switch out the kit and fire a few rounds of jacketed ammo. That will clean out the gas port and the bore. (Does not apply to actions incorporating a gas piston, which needs to be otherwise cleaned.)
I'm an incurable ballistics student (albeit not so venturesome where reloading manuals and my lack of lab equipment for pressure measurement is concerned). I've recovered jacketed .30, 8mm, .44, 9mm, and .45 bullets, both mine and commercial ones, fired after using lower velocity lead bullets. The jacketed followup bullets do a great job of dragging the lead out, and it stays on the jacket, even after the abrasion of going through several feet of wet backstop dirt and rock. They pick up lead even if you could not previously see it with a bore light. After it is gone, which only takes 3 - 5 shots, the recovered bullets come out clean. To me, that pretty thoroughly disproves the notion that anything has been "hammered into the bore". So for those of you who have been concerned about it, rest easy. I've done this a few times, to get rid of moderate lead in bores of guns bought at a show.
But of course, that's not the ideal way to approach the issue. Try not to get the lead fused in there in the first place. Use the right alloy for cast bullets, the right lube, the right powder, and understand velocity and pressure limitations...for the specific firearm and bore. By all means, don't be afraid of shooting lead bullets. I wish I could convince all of you who still have reservations. Cast bullets, some with gas checks, are almost all I shoot, even in rifles up to about 2300 fps. I have put thousands through my 1928 Thompson, at around 900 fps. IT-DOES-NOT-LEAD-UP! So stop worrying about leading a Smith. Best of all, lead bullets put almost no wear on a bore. On a $25,000 classic submachine gun, that's important. It is also important on a 70-year-old Smith which, to me, is like a fine painting. Save that bore, but shoot and enjoy it.
...which makes me pause to consider how wonderful S&W handguns of the golden era really are. Many of today's CNC-produced generation are even better, because modern tooling enables the mass production of bores with a remarkable surface finish, with good quality control management.
Remember what I said about my own mistakes? As a newbie reloader with a brand new S&W 36 Chief in about 1959, I thought it wouldn't hurt to fire a few rounds made with un-lubricated bullets, as I had run out of those black lube sticks for my Lyman #45 Lubrisizer. Those 148 grainers were so beautiful and shiny, how could it hurt? I fired no more than 20 rounds, hit no crows, and went home to clean the gun. Unbelievable. The leading was visible in strips and chunks that could be carefully pried off with a small screwdriver blade. Diameter was wa-a-a-ay below .357, and I'm lucky I did not pass the pressure limit. I was not "shooting" those last couple bullets; I was swaging them.
Now, that would have been the wrong time to use a jacketed bullet to try to clean out lead, as the jacketed projectile could not have been swaged down as easily as the lead slugs, and even that 2" +P Model 36 barrel or cylinder could have burst, or so I've theorized.
I've never used commercial chemical products to remove bore leading, because I've been religiously careful not to allow it to accumuate. And I've never had to use the reportedly excellent Lewis Lead Remover. I reload for over 30 different cartridges, thousands of rounds, for quite a few handguns, rifles, and a couple automatic weapons. And I don't get leading. I'm actually afraid of it, after my Chief's Special experience. And anyway, it is such a monumental pain in the butt to remove the stuff.
But thanks for tolerating all this maundering. I just wanted to share my experiences, as it has been so much fun learning all of the above, and it won't do me any good once they nail the lid shut. It would not have been nearly as much fun without all my wonderful S&Ws, and historian Roy Jinks is one of my heroes. The S&Ws are truly the best of the best, and I hail the company's resurrection. Now, don't go out there and use 450 grain jacketed hollow points to magically iron last weekend's residual cast bullet leading into the bores of your nice new $8,000 S&W custom shop .547 Magnum revolvers.
