April 30, 2018
Q: What's the difference between Boxer and Berdan primers? When were they developed? Mort Hutchings, via e-mail.
A: During the Industrial Revolution, in the last half of the 19th century, the munitions industry transitioned from using blackpowder to early smokeless propellants with substantially greater energy. Concurrently, loose components and paper cartridges with separate priming gave way to cartridges having a metal case that contained both primer and propellant with the bullet fixed in place. Initially, these improved rounds were inside primed; however, case designs evolved until the more powerful centerfire cartridges used a primer seated into an external pocket formed in the case head.
Eventually, two priming systems dominated. U.S. inventor Hiram Berdan developed a simple cup containing an explosive mix that was seated in a cartridge case having a complementing pocket configuration. The bottom of the pocket was formed with a round teat, or anvil, in the center and two small flash holes on either side. When the firing pin struck the primer cup, the explosive was crushed between the cup and anvil, and it ignited. The resulting flame passed through the two orifices and ignited the powder charge.
On the other side of the pond, Edward Boxer, in His Majesty's service, developed a similar device except his primer contained the explosive mix and an integral metal anvil. The cartridge primer pocket was a much simpler cylindrical cavity with only a single, larger-diameter flash hole in the center of the pocket.
I don't know why or exactly when, but interestingly, the Boxer design was adopted by the U.S. military and domestic manufacturers, and the Berdan scheme became prevalent in Europe and much of the rest of the world.
Obviously, the Berdan case head design is more complex. Forming the teat to an exact shape and size is critical so that the explosive pellet is positioned properly between the cup and anvil, which is required for the Berdan primer to ignite reliably. Punching or drilling a hole in the center of the Boxer-design case head after forming the simple cylindrical pocket is much easier to accomplish.
Granted, the Boxer primer itself is more complex than the Berdan design. Punching out the little two- or three-petal sheet metal anvils is not so bad, but precisely assembling them into similarly small, explosive-charged primer cups without mishap was probably a tough manufacturing hurdle in the beginning. Once a safe and reliable automated assembly method was developed, the overall Boxer primer scheme is clearly the more attractive method.
And that's doubly true for handloaders. Compared to a Boxer-primed cartridge, reloading a Berdan-primed case is a PITA situation. Instead of punching out the expended primer with a decapping rod that passes through the center flash hole while concurrently resizing the case body and neck, you have to externally pry out the Berdan primer using a special tool. You also have to avoid damaging the anvil any more than it may have already been when the firing pin crushed the primer cup onto it.
I've never decapped or loaded a Berdan cartridge, but I imagine verifying the condition of the anvil and that the two little flash holes are not clogged with residue so that you're certain your handload will actually fire when you squeeze the trigger would be a difficult task. On the other hand, if a new Boxer primer is seated with just a little amount of resistance, I'm confident the round will reliably and safely fire.
That said, I can't envision any circumstance where the Berdan priming system would be preferable to the Boxer scheme.