recurveman- For years I carried a cloth tape and measured the top-to-brisket heights of quite a few deer. For AZ whitetails, the smallest was 12" (a spike) and the highest was 16. The 16 was a big one with a 17 1/4" spread, and I'd say most decent three-pointers are 14 or 15.
I use this to estimate range by determining at which power the duplex part of the scope just brackets 15", or whatever. Might as well be optimistic!
Another thing I do is to determine how much elevation the point of the bottom post gives you. Most scopes are fairly close and on 9 power will give you 12 to 16". For instance, the Bush 3200 3X9 on my .270 gives me 12" at 400 yards, and the bullet drops just over 13 ( 2 1/2" hi @ 100 yds) at 400 yds. So if I hold on the top of the heavy bottom segment of the aperature instead of the crosshairs at 400 yards, the bullet will be an inch or two low. I determine all this with a yellow or white yardstick at a measured 25 yards (times 4, of course, to get the figure at 100 years, then go from there.) Looking at a ballistic program can get it close, but you need to actually go out and do it, especially if you don't have a chrono. Factory figures are usually pretty optimistic, both in bullet drop and velocity.