Fat man and little boy: a .50 caliber kick with .22 fun

Guns Magazine, Nov, 2004 by Dave Anderson

For More Information Contact: DPMS, Inc., 13983 Industry Avenue. Becker; MN 55306, (763)261-5600, www.dpmsinc.com

BlackHawk Industries, 4850 Brookside Court, Norfold, VA 23502-2052, (757)436-3101, www.blackhawkindustries.com

DEVELOPMENT OF THE .50 BEOWULF

Bill Alexander is a university-trained mechanical engineer with specialization in armor and defensive aid suits. He has a military background and has worked in many small arms programs. He notes, "For obvious reasons it is difficult to discuss much of this work but during this time I gathered much experience with small arms."

Alexander commented, "The development of the .50 Beowulf started in early 1999 in England. We were engaged in the latter stages of work on a tiny Personal Defense Weapon (PDW) cartridge and weapon.

"A large-caliber black powder enthusiast who was assisting with load development said, 'Why can't you get the M16 to shoot a bullet you can actually bloody see?' The idea was appealing.

"Design calculations for the rifle showed the M16 is well balanced around the 5.56x45 cartridge. To dramatically change the caliber, the balance must be maintained if the unit is to be safe and this is not as easy as it now appears.

"The M16/AR15 is governed by the head thrust it will absorb and by the mechanics of fatigue failure. To fit the largest bullet and to minimize the thrust on the bolt, a cartridge design will always move towards that of a straight case. This also increased the efficiency of the cartridge as the energy in the powder is converted better to projectile energy.

"Back in the workshop, the question was what cartridge we were going to use. We tried a shortened .50-70 carbine case with rebated rim, and while it looked impressive it would not work. We obtained some unfinished .50 AE brass. This reduced the cartridge diameter slightly and immediately solved the feed problems. After a good deal of analysis of the bolt, the rim dimension was set at .447 inch, which is identical to the existing 7.62x39 rim.

"Bolts for this rim diameter are already proven and offered significant increases in strength, life and safety. The case length was then set to fit an existing AR magazine with a 325-grain Speer bullet. We refined the angles at the cartridge base to ensure reliability and the .50 Beowulf was finished."

MAKING THE .50 RIFLE

The AR was designed to function with a small bore, high-pressure cartridge. Making it safe and reliable with a large bore, low pressure round took some thought.

Alexander comments, "The .50 Beowulf runs at a nice, gentle 33,000 psi. This in turn keeps the bolt safe. Using the straight-case design the cartridge has a high expansion ratio so the time pressure curve peaks quickly and then falls away just as quickly.

"Normally, AR-15 port pressure is around 15,000 psi to operate the mechanism, but in the Beowulf this occurs only 3 1/2 inches in front of the cartridge case. Add a port here and you get gun parts as the bullet is still in the bore when the bolt opens. The solution is to balance the pressure with the duration it will act and the time the mechanism takes to move.