Calibers and cartridges: The narrative behind the numbers in ammunition

“What exactly, does 7 mm/08 mean?” Christine wanted to know.

We were on our way home after spending a day in the big city, looking for a big game rifle for her. An opportunity for a caribou hunt had presented itself a couple of years after her introduction to duck hunting.

Having fallen in love with the connection to the country that hunting waterfowl brought her, she wanted to attempt to fill the freezer with one shot instead of many. With no experience to guide her, and never having had a big game rifle, she was sort of at my mercy for helping her to select one.

Her purchase of the Ruger 7 mm/08 came after considering the many options and settling on the rifle that offered reasonable dimensions, light weight, moderate recoil, and a cartridge suited for most any big game she chose to hunt.

The virtues of the rifle and cartridge came without a real explanation of what it the numbers meant. Who among us, besides those who had come under the tutelage of an experienced hunter or shooter, would know what any of the numbers, letters or names that grace the multitude of chamberings offered to American hunters/shooters mean?

“The 7 mm designates the diameter of the bore, and the projectile fired, and the 08 designates the parent brass case used to create the cartridge, the .308 Winchester. Or otherwise known as the 7.62 by 51 Nato,” I said in response to her question.

At that stage of our relationship, Christine had not learned that asking me a question about gun stuff brought forth an uncharacteristic diatribe. A virtual vomit of gun stuff that required in-depth explanation, which I delighted in providing.

“How would a person know that?” she asked and added, “There isn’t much about that title that tells me anything. We looked at another gun that was called a 7 mm; what was that?”

“That,” I said, “was a 7 mm Remington Magnum, and we looked at another 7 mm, a .280 Remington.”

While trying to stay focused on the road ahead, I could feel her stare that said: “What the hell are you talking about?”

“The .280 is also a 7 mm, although it actually fires a bullet that is .284 (inches) in diameter, as does your 7 mm/08, and the 7 mm Remington Magnum,” I said with the smug look of having the upper hand for a change.

“Well that’s just ridiculous” she said, “how is anyone supposed to know what is what with these names and numbers?”

Thinking this is really fun, I said, “It makes sense if you know the history. Take the .250-3000 Savage. It fires a bullet .257 (inches) in diameter and was the first commercial American cartridge to fire a bullet (in this case an 87-grain bullet) 3,000 feet per second.”

“Why didn’t they call it a .257-3000 then?” she asked.

“A lot of cartridges don’t follow the precise characteristics of the round. There are all sorts of designations that depart from what might seem sensible. Most of the time, it has to do with the sound of the name in print or when spoken word.”

“For fun, let’s say that when Clint Eastwood made the speech about ‘This is a .44 Magnum, the world’s most powerful handgun,” he had said instead, ‘This is a 42 Magnum, or a .429 Magnum.’ " (The true diameter of the bullets fired in the .44 Magnum are .429.)

By that time I was on a roll, and there would be no stopping my attempts to drag Christine into the fabulous world of cartridge terminology.

“Now,” I said, “take the .219 Donaldson Wasp, a .22 caliber cartridge that fired a .224 diameter bullet. The name has a spiffy ring to it. Were it the .224 Donaldson Wasp, not so much. Never mind that the parent cartridge was the .219 Zipper, which Winchester, as its creator, named because it zipped right along.”

“Are there any cartridges with a name that reflects what it really is?” Christine asked.

“Some,” I said. “The .375 H&H Magnum being a decent example. It fires a bullet that is .375 in diameter, the H&H stands for the London gun-making firm of Holland and Holland that designed it, and the case is large enough to justify its magnum destination. The bonus is few cartridges that have a nicer ring to the sound of the name.”

“I prefer shotgun terminology,“ she said. “It’s more straightforward.”

I agreed, shotguns are more standard and do not present the many options for creating new cartridges and, thus, new names. The destinations for cartridge length may be confusing. A 3-inch shotgun cartridge does not attain its 3-inch length until it is fired. Same with a 2¾-inch shotshell.

“American and some European shotguns are designated as 2¾-inch or 3-inch chambers while many European shotguns chambers are designated 70 mm, for 2¾, or 76 mm for 3-inch,” I said.

When I ran out of wind, Christine said she would never get it all straight and didn’t understand how I could have all this rattling around my head. I told her it was sort of like when she talked to me about yoga or espresso. I don’t know what the terms mean, and I probably never will, but I know it matters to her.

The things we humans find interesting seem always to develop a fun and unique language, and by virtue of its unique nature, perhaps unwittingly exclusive. But then that may be part of the fun, watching others come along to your world.

This may explain my delight from a few days ago when Christine called my hospital bed to tell me that the doctor had just told her the hole they plugged in my heart was 24 millimeters wide, and what did that mean.

My first instinct was to blurt out in genuine delight that I had a hole the size of a 20 mm cannon in my heart; if you gotta have a hole, it may as well be epic. But, knowing she would not have even a general idea of what that meant, I said, “Think of a hole the size of a 10-gauge shotgun, that’s about right.”

In the end, we mostly have the stories given to us through life experience and while I would have preferred not to have a hole in my heart, I am happy to be able to tell my gunning friends that yes, you could have stuck a 1,500 grain 20 mm bullet through the hole in my heart, now repaired. Much better than saying, “Oh it was about an inch.” The silver lining in the dark cloud.