hoghead,
i have had good luck with devcon 30 min epoxy...i use a heavy duty cut off disc on my dremel tool to cut a nice thin, even channel between the butt cap and the handle material all the way around. this gives you a uniform space that is wide enough to make sure you get good penetration with the gooey epoxy (i stuff it into the crack with a toothpick) and also leaves a fresh, laha free surface for the epoxy to stick to. this might seem a bit involved, but i dye my epoxy black so that it either matches the horn, or looks like a nice black spacer if the handle is wood (another reason to cut a regular channel out with the dremel tool). the only really tricky part is getting the epoxy to stay in the gap all the way around the handle...it wants to run out. i've had good luck with two ways around this, you can either mix up a good size batch of epoxy and sit there for a half an hour a keep ladling epoxy into the groove as it sets up, or seal off most of the groove with masking tape and then pour (or even better) inject the epoxy into the space. in either case you're going to need to do a little filing / sanding / buffing to get the excess epoxy off, but if you do a decent job,i think this solution ends up looking pretty slick.
blah blah blah...boy, i sure can run off at the mouth...
good luck,
e.