The Big One: .50 BMG (12.7x99mm)
By Chuck Hawks
There are bigger bullets out there, .577, .600, and even .700 caliber, but the .50 BMG is "The Big One." No other shoulder fired big bore caliber shoots as fast, as flat, or hits as hard. "BMG" stands for Browning Machine Gun. John Moses Browning devised it for his heavy machine gun, which first entered service with the U.S. military between 1918 and 1923 (depending on which source you believe) and is still in service today. It has been adopted by over 30 nations. The NATO designation for the cartridge is 12.7x99mm NATO. Browning's big .50 has now been in active service longer than any other contemporary cartridge in the world, and it performed admirably in the 2003 Iraq War, easily shredding the light trucks favored by Iraqi irregulars and terrorists.
Mainstream recreational shooters realized the sporting potential of the .50 BMG in the 1990's. Barrett, McMillan and a few others make .50 BMG rifles. In the long, heavy, bolt action target rifles created for it, the .50 BMG is the best 1000 yard cartridge in the world, often achieving 0.5 MOA 5-shot groups. (I cannot help but wonder what the "short, fat, sharp shoulder cartridge" crowd makes of the long range accuracy of the big .50 BMG!) The Fifty Caliber Shooter's Association (FCSA) sponsors long range .50 matches.
The .50 BMG is based on a huge, but conventional appearing, rimless bottleneck case. It has a .804" rim diameter, .803" head diameter, 15 degree 44 minute shoulder angle, 3.91" case length, and 5.45" overall cartridge length. It looks something like a scaled-up .30-06. Bullet diameter is .510" and all .50 BMG bullets are spitzers (pointed). Most cases are Boxer primed and made of brass, although mild steel cases have also been produced. A small magnet can be used to separate the two.
I don't know of anyone who has tried to prove it, but the .50 BMG delivers the bullet frontal area, sectional density (SD), ballistic coefficient (BC), and energy to make it a 1400 yard elephant rifle. At a more practical 400 yards, a range normally unheard of in pachyderm hunting, the .50 BMG (750 grain bullet at a MV around 2800 fps) can deliver 10,000 ft. lbs. of kinetic energy!
As far as I know, no factory loads for the .50 BMG are available from the major ammunition manufacturers, so the cartridge is strictly for reloaders. Surplus military ammo is available and is widely used as practice ammo by .50 caliber shooters.
The U.S. M33 .50 BMG military load uses a 668 grain FMJ-BT bullet at a muzzle velocity (MV) of 2910 fps with muzzle energy (ME) of 12,550 ft. lbs. The U.S. M2 military load uses a 720 grain FMJ-BT bullet at a MV of 2810 fps and ME of 12,600 ft. lbs.
At this writing, .50 BMG Reloading data is provided by Barnes, Hodgdon and Hornady. Commercial .509"-.510" bullets for the .50 BMG are supplied by Barnes (550 grain XLC-S, 750 and 800 grain FMJ-BT) and Hornady (750 grain A-Max BT). In addition, there are .510" RN soft point and solid bullets (usually weighing 500-600 grains) intended for the .500 NE and .500 Jeffery that could be adapted to relatively short range use in the .50 BMG. Slow burning powders are most suitable for the big .50. Recommended powders include Hodgdon H50 BMG, H870 and H5010, Viht. 24N41 and Viht. 20N29, and AA 8700. There are probably other providers who have not come to my attention that also offer data and components for the big BMG cartridge.
The following reloading data was taken from the fifth edition of the Hornady Handbook of Cartridge Reloading. Hornady used a McMillian rifle with a 36" barrel, IMI cases, CCI 350 primers, and their 750 grain A-Max UHC bullet (BC 1.050, SD .412) for developing all of their .50 BMG loads.
185.5 grains of H50 BMG powder provided a MV of 2400 fps, and 214.9 grains of H50 BMG provided a MV of 2700 fps. 186.5 grains of H870 powder drove the big Hornady bullet at a MV of 2300 fps, and 224.0 grains of H870 achieved a MV of 2800 fps. 218.6 grains of Viht. 20N29 powder gave a MV of 2500 fps, and 238.7 grains of Viht. 20N29 gave a MV of 2800 fps.
At a MV of 2750 fps the Hornady ballistic tables show that the ME of their 750 grain A-Max bullet is 12,592 ft. lbs. At 1000 yards the remaining energy is 6357 ft. lbs. The trajectory of that load from a rifle with a low mounted scope looks like this: +25.3" at 100 yards, +47.2" at 200 yards, +74.9" at 400 yards, 0 at 1000 yards, and -225.6" at 1400 yards.
For long range elephant hunting that load could be zeroed at 400 yards. In that case the trajectory would look like this: +6.6" at 100 yards, +9.7" at 200 yards, 0 at 400 yards, and -187.2 inches at 1000 yards.
Such hunting would require a hunter with a laser rangefinder and the patience to wait for a situation where he or she could shoot from a solid rest at a standing animal. Not to mention a couple of gun bearers willing to haul around a 30 pound rifle and protect the hunter's back with more conventional rifles.
The "Rifle Recoil Table" shows that a shooter with a 30 pound .50 BMG rifle firing a 750 grain bullet at a MV of 2400 fps had better be able to deal with some 68.3 ft. lbs. of kick. A 750 grain bullet at a MV of 2800 fps from the same weight rifle delivers a crushing 94.8 ft. lbs. of recoil energy. That is undoubtedly why every .50 BMG rifle I have ever seen is equipped with a muzzle brake.
Copyright 2003, 2012 by Chuck Hawks. All rights reserved.