With a .30 cal barrel 12.5 inches long and powered by 2 x 12g CO2 cartridges, it can do around 14 good shots (7 rounds in each magazine) with 44.75 grain JSB pellets at around 475 feet per second.
Here's a 0.30" pellet compared to a more traditional 0.177", quite a dramatic difference and around 7 times heavier.
Front piercing cap
Breech with magazine removed
[youtube][/youtube]
In action, it packs quite a punch and is pretty loud!
Some recovered pellets.