Georgia legalized hunting deer with air rifles a year or so ago. Been looking at the various options on the market.

Was wondering what everyone else is using.

Georgia allows 30 cal or larger with no foot pounds of energy requirement.

Realize that big bore airguns are really standard velocity handguns in a rifle form.  With that in mind, what caliber, bullet weight, and velocity (up to about 850 ft/s) pistol/revolver would you consider adequate?  

The rifle format does give you much better shot placement ability than a handgun which is a significant benefit, however, and may make you able to take longer humane shots.

Way back in the day when I deer hunted (with a rifle), my side-arm was a 4" .38 spl. revolver loaded with a 140 grain hollow point at low +P levels.  I felt that that was adequate for final dispatching of a downed mule deer, or when surprised by a trophy while otherwise occupied without my rifle in hand.   For me, a 35 caliber airgun pushing a 140 grain slug at 800 ft/s would be about my minimum for a smaller mule deer in my current neck of the desert. The maximum range would be limited to 150 yards as well, though hitting a deer at 250 would not be an issue, making an ethical kill at that range might be a problem.

That’s what I was thinking 35cal or larger. 100yards would be the max distance regardless just due to where I hunt at?

A friend of mine just got a new Umarex Hammer 50.   It shoots a 550gr .510 lead slug at 760 fps.
He's asked me to set it up, mount a scope, and sight it in for him, so I should have it in my hands in a few days.
He plans to go moose hunting with it.  

I have a Benjamin Bulldog 357 that hits pretty hard on steel targets

.45 caliber Bushbuck. 365 bullets. Far beyond Idaho's recommended 350 FPE.

I just sighted in the Umarex Hammer 50 with 320 grain Hollow Points.   Quite consistent muzzle velocities; around 880 fps
Not great groups at all; it seems VERY sensitive to wind.    "Minute of deer" at best.
Definitely don't want to be shooting big game over 100 yards with this; 75 yard limit probably better, both for accuracy and because the ballistics drop really increases after 75 yards.
Zeroed at 100, it's 6" high at 50 yards, 4-5" high at 75.   So 1-2" drop 50-75 yards, 4-5" drop 75-100 yards.
And that's with one of the lightest bullets available for this.   The 550gr would hit harder, but exaggerate the ballistics curve.

I wonder what it would do with a round ball and a PA sabot? I know you’re sacrificing energy but a round ball will get the job done.

What’s old is new:  the Lewis and Clark air rifle was of the same type once issued to some units of the Austrian Army during the black powder era.

https://en.m.wikipedia.org/wiki/Girardoni_air_rifle

The Austrian made PCP air rifle fired 20 or 30 round lead balls from one tank (in the buttock).  The balls were .45 (146 grain) or .51 caliber (201 grain).

Velocity was supposedly 600 fps.  Low, for big game, but I doubt that stopped Lewis and Clark from wounding big game animals with it, then finishing them off with their black powder guns.

Followup to the above story.

I did the above sighting for a friend who'd been given the rifle.   I put a high end scope on it.   Leupold Mk5HD, I believe, with Backcountry rings.  

I sighted it in OK.   Things seemed to move around some, but I finally got it hitting minute-of-deer at 100 yards, so I gave it back to my friend and told him it was good to go.

This was back in July.    

Come about September or October, my friend said he hadn't had time to shoot the gun, but he was going moose hunting in a week or so, and he asked me to come by and run through the charging, loading, and shooting procedures with him.

I went over to his place and he started shooting it.  First shot, missed the backer entirely at 100 yards.  Same with second shot.  We moved to 50 yards and  finally got a hit about a foot high left.   WTF??   This is a new high end scope, high end rings, professionally installed, lapped, torqued.

We diddled with the scope, reset zero on it, shot some more.   It would shoot one or two OK, then throw some big flyers.  And this is using no more than 3 shots per charge and making sure gauge is over 3000 on third shot.   After a bunch more diddling, we got it "sort of" shooting OK.   I left, my friend said he'd shoot it more later.

Last I heard from my friend about it, he never did get it shooting well enough to be comfortable shooting it at a moose.  He gave up on it and took his regular rifle.  He did get a moose.  ;-)

I know when my friend was given the rifle, it had what my friend called a "crappy" Vortex scope on it.   Perhaps his friend who had given it to him experienced the same issues and attributed it to the scope.  I'm not sure on that.

Anyway, I don't know it that one was just bad or if they're all like that, or what the problem might have been with this one.  
So bottom line is I wouldn't trust that thing at all, especially on a hunt.