Hey D80, 8 to 12 hours in the dehydrator is a LONG time, which may be why you've had better luck with ground venison.

Odds are you are over drying it. In my experience, most jerky is done within 4 to 6 hours, but it certainly depends on the thickness of the end product, you may be spot on with 8-12 if your jerky gun is making a thick stick. It should bend without breaking when it's done, and if you tear a piece and squeeze it at the tear, there should be no moisture - it's a real fine line to hit, but it's fine if it's a little over or under.

If you are getting that many deer, you should practice more with some sliced top or bottom round roasts off the rear quarter. I have nothing against using ground, but most people seem to prefer the sliced when it is done right (myself included). Do a pound or two at a time till you master it.

There's an article on testing for dryness here, with other jerky tips too if you are interested. If you are making as much jerky as it sounds like, I'm sure friends/family will appreciate some variety!