Man, I didn't know these things existed. Two weeks ago, they held the Standing Stone Rendevous here in Corbin. Air rifle shooters from all over the US and Europe showed up to shoot everything from .177 pellet guns to a monster .58 caliber bolt action air rifle. That .58 caliber was one awesome machine. It shot 650 grain maxiballs and obliterated a steel target at 40 yards.
Gary Barnes was the guy who built this firearm. It was something to see. Very capable of killing an Elk or Black Bear. I'd be hesitant on a Grizzly simply because of the shot limitation of the air supply. They powered these things with compressed air from a dive cylinder. The 58 cal at full power could get 2 shots to a charge, maybe 5 at the lower pressure they were using to keep from killing the targets at the range.
Have you ever seen such rifles? Like I said, I didn't know they existed till I went to this thing. I knew there were a lot of small calibers around, and like everyone else I know, my first rifle was a Red Ryder, but this is just way past that. The big guns were very much equivalent to traditional muzzleloaders as far as power goes.
Here's some pics of the guns I took while I was there.
http://skipsoutdoors.com/Forum/showthread.php?t=2962Skipper