Brinell hardness testing was developed in 1900 by Swedish engineer Johan August Brinell. It was the first widely used and standardized hardness test in engineering and metallurgy. In simple terms it is the indention measurement of an item that was hit by a specific metal ball on a test fixture. It is the general standard that most people use to discuss the hardness of a specific bullet. The BHN or Brinell hardness number is derived from this test and put on a scale. Brinell testing can be used for all types of bullets from solid copper to pure lead. We are focusing on pistol bullets in their three general types, copper jacketed, copper plated, and lead cast.

BHN Evolution

Originally, muzzleloader bullets were cast from pure lead, typically measuring a BHN of 5. This choice ensured that the bullet could be manually driven down the bore, effectively sealing it. However, advancements in firearms technology led to increased pressure during firing, causing pure lead bullets to strip through rifling, thus compromising accuracy. To address this, antimony and tin were introduced into the lead mixture at varying levels to enhance bullet stiffness and maintain shape and grip. In contemporary contexts with modern powders and handgun rifling types, a lead bullet in a standard velocity cartridge typically boasts a BHN of 8-12. For higher velocities, a harder bullet with a BHN of 12-16 is recommended. For instance, the Lyman #2 bullet lead mixture, consisting of 92% lead, 6% antimony, and 2% tin, yields a BHN of 15.

copper jacket

Copper jacket bullets differ significantly in construction, featuring a jacket outside and a lead core inside. This design allows the copper jacket to withstand higher pressures while remaining malleable enough to conform to barrel rifling, ensuring a proper seal in the bore as it traverses the barrel propelled by powder gases. The copper jacket absorbs the brunt of the force, while the lead core inside must possess sufficient hardness to support the jacket. Typically, copper jackets for pistol bullets exhibit a BHN ranging from 89-114, while the lead inside comprises 98% lead and 2% antimony, yielding a BHN of 10.

precision BONDED BULLETS

At Accura Outdoors our precision bonded bullets are the perfect blend of copper plating and swaged lead cores. Our pistol bullets begin life as lead billets with 97% pure lead and 3% Antimony. The billets are then extruded into specific diameter lead wire for each bullet caliber. The lead wire is processed through a bullet swage die that shapes the bullet into its basic profile with a BHN 8. Those bullets are put through a copper plating bath until they reach the desired weight and diameter. The plated bullets are restruck in the final die to give them their completed shape and diameter. Copper plating also adds to the BHN for the finished bullet at about BHN 15.

The perfect BHN for different types of bullets has been tried, tested and argued for years. The primary issue for every bullet is material cost. Lead is by far the cheapest bullet material and makes up the bulk of each projectile. Each metal or manufacturing process that is added to the lead brings with it a cost. Cast lead bullets offer reduced cost with added barrel fouling and lead smoke. Jacketed bullets require the most expensive components and manufacturing processes, but they have reduced fouling and no lead bullet smoke. At Accura we believe that our precision bonded bullet line provides the best of both worlds. Through our extensive testing, we have found the perfect blend of quality, accuracy and affordability.