I have been shooting BP guns, both MZs and Cartridge since I was 14.
I am 54 now so that makes 40 years so far.
I have used Elephant brand, Goex, Swiss, Pyrodex, Tripple 7, Clean Shot, Clear Shot and I can tell you that it is all corrosive.
It all will cause a gun to rust if it is not cleaned properly
The only one I have not used is BH209 so I can't say if it is corrosive or not.
As far as clean up goes, I never use water on a gun!
Used to do that and had nothing but rust problems.
Now I use a good bore cleaner of different brands and follow that up with a complete wipe down inside and out with Rig grease and have never had another problem with rust on a gun since.
As for the brass casings I do clean them with soppy water, let dry and them tumble clean.
Have been thinking of getting one of the new ultra sonic cleaners to try on brass used for BP and see how well it does.
I also have a few rolling blocks that I shoot.
Two 7x57s (one a 1897 #1 action and the other a smokeless 1902 #5 action) and three #1 action 1879 Argentine models (one rifle in 43 Reformado and one each, rifle and carbine in 11.15x58R) along with a #4 in 22 cal.
I was lucky enough to have found a good supply of new bell brass for the 11.15 back in the 70s along with 80 rounds of new ammo.
In BP form the 43 holds a few grains more powder than does the 45-70, 77-78 IIRC.
I can tell you that the 43 will put a deer down just as fast as the 45-70 also.
In the real world you can't tell the difference between the two loadings, 45-70 with a 405gr lead bullet or the 11.15 with a 385-387gr lead bullet when loaded with BP.
Both hit between 1300-1400 fps out of a standard length rifle barrel.
LONGTOM