Just thought I would add my 2 cents to the BH209 corrosion subject, a year or so ago I took an old (junk actually) CVA ML rifle and an Italian C&B revolver in similar condition and fired both with BH209 then stored without cleaning to see what would happen. The sidelock ML was very hard to ignite and took several caps to each shot before it would fire but I did get it to discharge a few rounds, I went through 12 shots with the revolver. At first not much happened at all then after a week I was getting rust around the nipples, I assume from the residue from the cap, this got even worse after a couple of weeks but there was no rust or any signs of corrosion anywhere from the BH209 powder! It did create a dull "Greyish" powder like layer but this easily cleaned off leaving no signs of corrosion. Under similar conditions I am sure Pyrodex would have destroyed the bores in these guns but apparently the 209 is not at all corrosive, at least I couldn't get it to produce any signs of such.

Brass cases are another matter for some reason and while it doesn't seem to damage them it sure turns the brass dark, very dark, in a very short time. Still I really liked the stuff with two exceptions, it doesn't light off worth squat in a side lock ML (to be fair it's not meant for such systems) and it just costs too much! If they would get the price within reason I would shoot a lot more of it, my 45-90 works really well with BH209 but I can go through one of those $35 jugs way too fast!

I am not sure how much if any sulfuric acid is produced but I couldn't get any signs of corrosion on the steel at all and the darkening of the cases showed no signs of etching and no greenish residue, other than the brass turning dark it didn't seem to harm it and after many loading since using the 209 it is still holding up just fine. There are several chemical reactions that can affect brass coloration that aren't corrosive, not saying that's the cases here but I couldn't get any rust/corrosion effects on the steel and I tried!

That pistol remained untouched for months with no change except for a bit heavier rust around the nipples where the caps had fired, even through the humidity of this past Summer the last time I saw it was when I gave it away and it still had no rust in the bore. The pistol was rather shabby anyway so I wasn't concerned with it, the ML rifle however was worth saving so after the initial two week period I cleaned and oiled it and put it away until it too was traded off some months ago. It was pretty conclusive to me that the BH209 does indeed live up to it's claims and it sure seems non-corrosive to me, orders of magnitude better than Pyro!