So you want an AR-15 for hog hunting that can launch .40 cal (10mm) pills? This wildcat caliber might be what you are looking for. It is called .400AR and was developed for hog hunting. The designers had initial requirements to have the largest caliber that will allow having double stack loaded ammunition in magazines fitting into the AR-15 magazine well. They also wanted to have at least 2,000 ft-lbs (2,712 joules) of muzzle energy and be able to use one of common cartridge head sizes which would allow using an off-the-shelf AR-15 bolt.

The new cartridge also had to have a maximum pressure manageable by the AR-15 platform. The development of this cartridge started three years ago with the first chamber cut back in the summer of 2014. The designers came up with a .40 caliber cartridge which is based on 7.35x51mm Carcano case. Initially, they cut the Carcano case right below the shoulder which gave them a 1.6″ long case. However, later they changed the design and made the final case to be 1.7″ long. The Carcano case has head (.447″) dimensions identical to that of 7.62x39mm cartridge, which means that they could use 7.62x39mm or 6.5mm Grendel bolts.

They started they tests with 200 gr .40 cal muzzle loader bullets and after a number of tests, they reached the set goals. The .400AR final load launches the 200 gr projectiles at a muzzle velocity of 2,312 fps with 2,374 ft-lbs of muzzle energy (at around 50K PSI of pressure). It also reaches pretty interesting numbers with .40 cal handgun bullets. Particularly, it pushes the 135 gr bullets at 3,042 fps.

I think the same results could be achieved if the cartridge was based on a .422 head size (.30 Remington, 6.8 SPC etc). But that would be a straight walled case whereas .400AR should have a slightly tapered one, which is good for feeding reliability. If the case taper is ignored, then they could use larger projectiles of .423 cal from .404 Jeffery cartridge with the .447″ case body diameter. But then again case taper is good and the .423 is a rather odd caliber compared to the 10mm/.40 cal.

There is a website dedicated to this cartridge, where you can read more about it by clicking here.