While working for a couple of BPCR makers and shooting BPCR competition I had opportunity to examine a lot of guns, do some testing with company guns and see the guns used by customers and competitors.

If you have some of these powders polish a 1" wide by 12" long piece of steel so that its perfectly clean on one side. Belt sander will work.
Place a paper over one end and flash a small pile of BP on the other. Then cover the BP end and flash the other stuff on other end.
Set in some dry place (free of physical water, a shelf in a shop or house will work) and check periodically. In low humidity Montana the BP end will not rust in 2 weeks (remember the 30% humidity thing with BP). Not so the other end of the bar.
I have never seen a gun used to any extent with the corrosive powders that did not show evidence of what was used. BP is far less of a problem and I know of rifles that have been shot for years and 10s of thousands of rounds with BP and the bores look just like new.

One must be careful "naming names" when dealing with a company with lots of money for lawyers. Believe it. The truth is no defense against the lawyers.
The magazines (other than a letter to the editor in Rifle or Handloader years ago about a barrel ruined over night) just will not publish anything that might damage an advertiser.
Trust me.
So do your own careful testing make your own decisions based on that.
Dan