You can use sabots in an air rifle just like you can in a shotgun. You get a higher velocity with more shock and better trajectory. The sabot allows you to use a smaller caliber bullet in a larger bore. 50 caliber sabots allow you to fire a 45 caliber bullet from a 50 caliber rifle. The lighter weight bullet achieves a high velocity.
Hornady and other manufacturers make sabots for muzzleloaders but you can use them in a air rifle too. They work the same way.
These are 50 caliber sabots with a Hornady 250 grain SST bullet.
You can use any brand sabots and then insert whatever bullet you want. Here are some other brands of sabots.
Now all you need is a .50 caliber air rifle to shoot these. Several manufacturers make them like Sam Yang, Dragon Slayer, Quackenbush, Extreme Big Bore and XP Airguns.
Here is a demonstration video of sabots being used in a 50 cal Sam Yang Dragon Claw air rifle. It is pretty amazing.
Here are some 50 cal sabots for sale..50 cal sabots at Amazon.com