Let's not go admitting how many mistakes we've made that cost money; it sets a bad precedent! All those horns were planned that way, I wanted to make rum horns and salt horns and such.
Doesn't look like anyone is going to believe that, so let's just say that at one point I must have had about 20-25 assorted salt horns, rum horns, horn cups, and powder measures in my box of trade goods. When someone would comment on how nice the horn was, or that they wished I would have made a powder horn with it, I'd just shrug my shoulders.
After a while I noticed that when thinning horn with a file I could hear the difference in the sound as it got thinner . . . . so I sacrificed a few horns that weren't quite what I wanted for size or shape or color. I filed til I thought the sound was indicating the right thickness or minimum thickness, then cut the horn open on a bandsaw so I could actually see the thickness.
It helped. You sort of get a feel for the thickness after a while. And I notice that almost every horn maker turns out the occasional salt horn.