I'm not so sure that the heat has so much to do with it. The flame and pressure lasts for probably a millisecond. There no doubt is gas erosion and maybe some particulate cutting. Now if you are shooting long enough to heat treat your gun, that's another matter. You do have to match your bullet hardness to chamber pressure though.
I myself have never loaded lead bullets with Lil' Gun, I am only going by what others have told me. If there is enough heat and particulate cutting to eat a forcing cone, I assume there is enough to eat the base of a lead bullet as it passes thru the cylinder gap. I would also assume this would contribute to a poorer fit and thus leading. Not leading from just melted lead. I dunno. I do know there is relatively little if any published data using Lil' Gun with lead. That tells me something. If it were me and I wanted to push lead to max velocities with Lil' Gun, I'd probably use a GC. Again, JMHO.
Just trying MANY different powders to see what produces the most desired results. Lil' gun haz been mentioned by many to be a good choice in thier mags.
Half a dozen years ago, Lil' Gun was touted as the "Holy Grail" of powders for Magnum handgun calibers. Higher velocities than obtainable with H110/W296, 2400 or IMR/H4227 with considerably less pressure. I never found that to be true. What I did find was my guns got considerably hotter in considerably less time than when shooting any other powders. Didn't matter if they were my revolvers or handgun caliber carbines. When the reports of excessive premature forcing cone and top strap erosion came out, it was easy for me to believe. It was easy for me to walk away from Lil' Gun because it did not produce for me, any better velocities, or accuracy, in the calibers and bullets I was using. I never was one to load for highest velocity tho, only highest accuracy. In the last few years, you find few if any threads like this about using Lil' Gun in revolvers. This too, tells me something.
IMR4227 gives me my best accuracy in .44 mag and .460 mag with the projectiles I use. It is a tad dirty when not loaded to compressed or nearly compressed, but that does not matter to me. In .357 mag, the old standby H110/W296 gives me the velocities and accuracy I want for hunting, again, with the projectiles I use. I shot up the last of the loads I had using Lil' Gun in my carbines and I still have half a jug left. The cost of letting it sit, to me anyway, is much less than the cost of potential damage to my revolvers. Others are free to fell differently.
