sometimes there just isnt enough time to figure out what it is.
I think you do belong to the "theres a deer, bang" group. Personally if I dont know what kinda deer I'm looking at, then I dont shoot. Its really that simple. If he/she runs off, o'well I'll get them next time.
I would really like to know how people can tell the differance.
Theres a thing called Binoculars, get a pair. Its really a very amazing "gadget" you just look through the eye piece and bang, you can tell if its a bb, doe, or 160"+ buck.