I've participated in the last few 'Big Bore' air rifle shoots in this country. The year before last ony guy had a home built model that shot a 3000 grain slug that developed over 1000 foot pounds of energy. A new world record. I have a Stoutenmeyer of London Butt resevoir rifle that shoots a ..62 calibre ball at approximately 650 - 700 feet per second. That's enough to take a deer at up to 25 - 30 yards.
There are quite a few large bore airguns out there now. Check out this web site:
http://ns.connext.net/~glbarnes/ He makes some very nice large bore airguns.
The Antique ones were made all the way back to the early 1600's. They used either a Butt resevoir, Ball resevoir (under the reciever or sometimes over the top of the reciever) and in rare cases they even had a barrel resevoir. This was a shroud over the barrel that acted as the air storage. Lewis and Clark brought one along on their expedition. It is commonly believed to be a Lukens of Philidalphia and is believed to be the one at the Virginia Military Institute.