This is the 14.9x102mm SOP, a wildcat cartridge made by necking down a 20mm Vulcan autocannon shell casing. It was developed as a collaborative project among members of the Snipers Hide online forum. It has undergone several revisions since 2010.
It’s usually loaded with a hand-crafted low-drag 1,690 grain solid copper bullet, which it fires at roughly 3,350 fps. The projectile itself is roughly 4 inches long, with driving bands and an aggressive rebated boat tail to reduce base drag.
The sectional density is around 0.70, which is an astoundingly high measure of the mass-to-diameter ratio. It’s very heavy for it’s caliber, nearly a quarter pound.
The ballistic coefficient is about 1.85, which is an astoundingly high measure of how aerodynamic the bullet is during flight.
Here’s one unfired bullet next to a recovered bullet:
At the previously stated muzzle velocity, the bullet is carrying about 42,000 ft-lbs of kinetic energy. It remains supersonic out to 5,000 meters, or 5,400 yards.
For comparison, a similar monolithic bullet in .50 BMG usually maxes out around 800 grains at 2,900 fps. It has a sectional density around 0.44, a ballistic coefficient around 1.13, and it’s carrying less than 15,000 ft-lbs of energy at the muzzle.
For further comparison, you’d be hard pressed to find a 5.56 load recipe that hits 1,400 ft-lbs.
Here’s a comparison image of the three examples: one 14.9mm, one .50, and a stripper clip of green tip 5.56 NATO. The 14.9 is coated in black molybdenum disulfide film, which acts as a lubricant and helps extend barrel life.
Needless to say, the rifle that fires this colossal cartridge is appropriately huge. Currently, the test gun is a single-shot bolt action, which wears a 48-inch super-heavyweight bull barrel. The entire gun weighs in at about 100lbs, due to deliberately added weight.
This weight helps dampen recoil to a survivable level, although the designers suggest that a recoil-reducing stock, giant muzzle brake, and lighter barrel profile could bring the weight down to 30 lbs without inflicting enough blunt force trauma to kill the shooter.
At least a few other prototype rifles are under construction, include some magazine fed repeaters. Due to laws against rifled bores larger than .50 caliber, each 14.9mm (.59 caliber) must be federally registered as a “destructive device”.