Current Rifle Cartridges
.277 Wolverine or 6.8x39mm
The .277 Wolverine (6.8×39mm) originally started off as a wildcat cartridge developed and marketed by Mark Kexel,
President of Mad Dog Weapon Systems. Brass became available in 2018.
It was developed for the AR-15's platform rifles and pistols which if chambered in .223 Remington  (5.56×45mm NATO)
caliber will only require a new barrel to upgrade/convert any 5.56-based firearm to .277 Wolverine.
Please note, in the above pictures, the picture on the right, for size comparion : Left .223 vs .277 on Right.