what is this? what is created from?? Thia was on a H&R Handi rifle.

It is almost the same as a 300 Whisper. Basically a 221 Fireball necked up to 30 caliber. Designed to run in an AR 15 that is suppressed and still cycle the action. Can also run it un-suppressed.

Web site dedicated to the cartridge. http://www.300blktalk.com/foru...ae9f4a6f1c7f9a214d2f

Another feature is that 300 Blackout ARs can use the same magazine as 5.56 ARs.