This article described our steps in Forward Spotter Bunker Design.
We could be wrong. Don’t trust this article, do your own testing!
In our preparation for our world record attempt in the summer of 2022, we needed to know what kind of steel to use. The bullet would be a 422 grain solid copper bullet descending at about 48 degrees from 4.4 miles away. Our world record attempt / success story is HERE)
Our team did some initial math, or as Cirque Innovation engineer Wes Womak calls it; “noodling.” and thought that a heavy solid copper Buffalo Bore bullet from a 44 magnum at 100 yards would be close to equivalent. The test passed, with 3/16″ A-36 steel at a 80 degree angle, denting the metal deeply, but not penetrating. Still, we wanted to be extra sure. We turned to our mentor David Crandall, a retired engineer who specialized in small arms related things, as well as being a competitive shooting champion and serving for four years as Captain of the U.S. Veterans Rifle team.
Limited Penetration Testing of Copper Projectiles on Sheet Steel
Disclaimer: The authors and test personnel do not represent the above information to be accurate, reliable or suitable for any use. Those needing information on copper projectile penetration in steel should design and conduct their own testing.
Test projectile assemblies consisted of .408 diameter 395 gr MTAC Cutting Edge bullets seated in muzzle loading SABOTs for loading in 458 SOCOM cases. The Cutting Edge bullets were also wrapped in a one layer band of electrical tape and then covered with heat shrink tubing to bring the forward bearing portion up to approximately .450 diameter to hold the projectiles in better alignment with the gun bore. Low velocity test loads used 7 grains of Red Dot powder. Higher velocity loads used 19.1 grs of N110 powder.
Personnel shielding consisted of approximately 1 ¼ inch of wood backed with 3/16 A-36 steel plate to stop rebounding projectiles. Target material consisted of 3/16” and 10 gauge (≈ 1.134”) A-36 sheet steel set approximately 10 inches forward of the SOCOM caliber rifle muzzle. The short flight distance was set to assure the projectiles were point forward at impact. The slower twist rate (1 turn in 20 inches) of the SOCOM rifle was known to be too slow to stabilize the long heavy Cutting Edge projectiles for greater flight distances. A short (≈ 4”) section of 1” OD radiator hose was attached to protect the rifle muzzle from rebounding projectiles.
The rifle was set in a dismounted car tire, lifted about four inches at the side under the rifle butt using 2 x 4 wood blocks, to bring the rifle barrel level. The barrel surrounded by the radiator hose was inserted through a 1” hole in the steel and wood personnel shielding. The rifle barrel was aligned to deliver projectile assemblies on a line perpendicular to the sheet steel targets. A long lanyard was set up so the rifle could be fired while the observers stood behind a parked car.
Final Armor Test occurred on the morning of September 1, 2022, with David Crandall and Scott Austin present. Test occurred on the IFSA Range west of Idaho Falls, Idaho. On the day of the test, velocity was measured for both loads (3 rounds each) using a Lab Radar chronograph. The low velocity loads produced 803 fps with SD of 7 fps. The higher velocity loads produced 1122 fps with SD of 14 fps.
Two rounds of the higher velocity load were fired at and fully penetrated the 10 gauge sheet steel. Two rounds of the low velocity load were fired at the 10 gauge sheet steel resulting in failure to penetrate, however, the steel was cracked at one of the two impact points. The low velocity load produced dents in the 10 gauge sheet steel.
Two rounds of the low velocity load were fired at the 3/16 sheet steel resulting in failure to penetrate. Four rounds of the higher velocity load were fired at the 3/16 sheet steel resulting in failure to penetrate but produce slightly deeper dents than those produced by the low velocity load.
Low velocity projectiles that rebounded and were recovered were generally bent into a banana shape. Higher velocity projectiles that rebounded and were recovered presented flattened and mushroomed points. Virtually all the dents made by rebounding projectiles in the wood personnel shielding were round suggesting they were made by the bases of the projectiles.
The authors and test personnel do not represent the above information to be accurate, reliable or suitable for any use. Those needing information on copper projectile penetration in steel should design and conduct their own testing.
After David provided the information, Shepard set about completing his 3rd iteration of Forward Spotter Bunker Design. More details coming soon!