Tinker,
Yes, I have used them on deer and they worked extremely well. I never recovered a fired slug to examine though, they have always excited the animal. To answer your next question, No, I have not tried any harder alloy in these slugs because I didn't see any need to do so. Even though we think of water as being 'Soft', it causes bullets to flatten just about like they would if they had hit a block wall. That is why the slug looks so stressed. Deer chests are much "softer" on soft lead bullets than jugs of water, hard as that may be to believe.
Also, I make them soft because I want to, they seem to work well and a slug that dumps most, if not all, of it's energy into the animal seems to kill much quicker. I agree with what was said about soft muzzleloading bullets killing well, even though they were radically slowed down from their enitial muzzle velocity. That is the energy dumping soft lead bullet of decent weight, still doing its job well. This 20 gauge double gun is used to hunt just like I used to hunt with the muzzleloader, get close, and put the slug where it will do the best job. No problems so far.
Bob