I've used some of the drum dyed horse butts from Springfield. Interesting stuff. It is not soft jacked in the general meaning of the term and I suspect a different tannage than the regular veg tan horsehide. On the ones I received the flesh side is much nicer than the grain which had cracks and stress marks all over. The flesh side is a very fine nap almost like microfiber and is really pretty. I've been using it for rough out pocket holsters and it really grabs. I did note that this stuff takes water as quick as cowhide and molds nicely although it doesn't stiffen much when dried and I had to use a different method to make it stiff.
Normal soft jacked horse, which I prefer for regular holsters, will case quicker than hard jacked but still much slower than cow and I believe molds and forms better. YMMV. In that case it is only a matter of compression not tannage as soft jacked will stiffen nicely when heat dried.