I'm not sure I agree that a 12 ga. slug is requried to put down a wounded 1?0 lb. deer at close range, as opposed to a .45ACP, but that's a discussion for the hunting forum, probably.
No, it's not required, but I don't always have a .40/.45/10mm/.357 with me. The 870 was a freebie that I just had to put a little time and a couple bucks into, so I don't really care if it gets beat up (more) or a little rusty riding around behind the seat.
The mulies are thick here; You can't drive very far without seeing a fresh kill most days. Most of the time, the deer are already dead by the time I see them, and the majority that I've actually seen get hit expired quickly. More than once I've got out with gun and walked over just in time to see it take it's last few breaths, then check for pulse and, if I have time and it's not completely destroyed, load it up. However, the ones that get hit in the rear end tend to be badly broken but very much alive.
If i didn't feel confident my concealed carry gun was safe to euthanize an injured deer with i wouldn't feel confident in it for self defense either. I do have a Ruger LCP but only carry it when no other practical option exists and to be honest i believe it capable of humanely killing a deer with a headshot.
You've never dealt with an injured deer, have you? When they're writhing around with broken hips, they're very much alive and you
really don't want to get that close. I'm a decent shot with a handgun, but deer have tiny brains and fairly tough skulls. Odds are you'd have to shoot it more than once with a typical handgun (the 10mm I used was stoked with my own loads that far exceed typical .40 or .45 power), and that's just not ethical. With a 12 ga. slug, one or two through the boiler room and it's lights out.
Sure, I could just keep a larger caliber handgun in the vehicle instead, but why? If it's gonna live in the car anyway, it may as well be a more powerful (and less expensive) long gun.
It is lawful to dispatch and even claim car-injured animals here, though adviseable to call it in so no one thinks you're poaching.
Eh, not really out here. Does tend to be closer to 150-200, but it's not terribly uncommon to see 300+ lb big bucks around here.