Yes it's a Precharged Pneumatic Gun (PCPs).
A 50 caliber Pellet gun (rifle) is a precharged pneumatic air rifle. It uses a scuba tank or compressor to charge the rifle. It can fire up to a 50 cal pellet. Companies like Shin Sung and others make air rifles this large. You can find the on the web. Places like "Pyrmyd air" sell them.
Shin Sung Career Dragon Slayer. 50 Caliber, Sam Yang Reclusive .357 cal or Sam Yang Dragon Claw .50 Caliber. Any one of there are suitable for larger game.
When you say Air Rifle you are referring to a pellet rifle not a firearm. At present there are no 300 Cal air rifle being made.
It all depends on the rifle, pellet and power source.
OKAY: What is you queston?
Rodents and small game.
Definitely Yes it can.
Some air rifles were available in .22 caliber.
No. Just have to be old enough!
Rodents
The Benjamin 132 is an air pistol not a rifle, it uses .22 caliber pellets, not .177 caliber pellets. The 130 series of Benjamin pistols were models: 130 shot .175 Cal BB's 132 shot .22 Cal pellets 137 shot .177 Cal pellets If yours is a rifle then I have NO idea what it shoots
Gamo Hunter Extreme 1650 FPS - Air rifle .177 Cal Air Force TalonP 900 FPS air pistol .25 Cal Hatsan AT P1 Air Pistol .177 870 FPS The Air Force TalonP is faster in .25 Cal than the Hatsan .177 Cal