.22 Accelerator
The .22 Accelerator is a special loading of the .30-30, .308, and .30-06 cartridges that is manufactured by Remington. Description
It consists of a sub-caliber  diameter bullet, held in a .30-caliber  six-fingered plastic sabot with a hollowed base. The bullet separates from the sabot approximately  from the muzzle. Usage
The cartridge allows for using a large-caliber rifle for varmint shooting, although the accuracy is somewhat diminished. The advantage, however, is the extremely high muzzle velocity from factory-loaded ammunition. References

Pistol and rifle cartridges