Back 10 or more years ago I had a chunk gun load consisting of 20 grs of pistol pyrodex on the bottom & 100grs of pyrodex "select"?? (I think that's the right word, it's been a while) on top.
If I cleaned right it was no problem. My gut feeling is that if left uncleaned it would get ugly. For whatever that's worth. If we drug a gun home on a rope behind our truck it would screw it up also. So we don't. We clean BP or pyrodex properly & there ain't no problem.
Most of the war stories start with a barrel left uncleaned from last years hunting. And of course the thing is junk. I've seen both BP & pyro. where this year long abuse destroyed a gun.
I would bet, based on my experience, the barrel shot with Chlorate powder to any extent can be identified as such by looking IF the observer knows what to look for. The "dwell time" between shots is enough, over time, to cause problems.
If the stuff is cleaned like for BP I KNOW the barrel will show it if used much.
Debreeching or borescope would tell the tale. Its POSSIBLE that the barrel is unpitted but I would bet that it was. Often its very tiny craters when magnified that may not be noticed unless the observer knows what he is looking at with the naked eye. Once the observer understands what he is looking at its instantly identifiable.
Proponents just love to assume that the people failed to clean the gun correctly. While I am sure this is the case in some instances. Its not the case in ALL and conscientious bore cleaners still have problems.
A guy I know pretty well shot the stuff in an original 1869 TD in 50-70. It took a YEAR to stop the after rust. He finally stripped the barreled action from the wood and took it in the shower and heavily flushed it and he got the salts washed away and it finally quit rusting.
He was highly experienced at the time, probably 20 years ago, and certainly was no neophyte.
People that think the stuff is no worse than BP need to look at the various military rifles shot with milspec corrosive primers. These have perhaps a 1/10 of a grain of "active ingredient" Potassium Chlorate the chlorate powders are 17% +- Potassium PERchlorate. Both of which produce virtually the same result on steel. It destroys the iron at the molecular level and will even eat "crawdad holes" in barrels and breeches. This has ALL been seen in disassembled firearms since the advent of this stuff.
For reference I have owned and or worked on rifles that were shot with BP and not cleaned for an entire Silhouette match to preserve a consistent bore condition. This means being left "dirty" for several hours at time. These barrels do not rust. I know of guns that have been in service for long periods and shot 10s of thousands of rounds with BP loads and the bores are still perfect.
This simply is not possible with powders with Chlorate components. The fouling is just too aggressive and difficult to remove adequately. Wiping between shots may actually increase the problem unless ALL the fouling is removed as soon as the wiping is started. Wetting the stuff activates it. Even Hoppe's original #9 (not 9 Plus) will cause it to pit a barrel seriously if left uncleaned overnight with #9 in the bore. A common practice with non-corrosive powders.
Dan