Why are there so many calibers?

And what are they all for?

I’ve heard questions like this asked many times: “Why are there so many calibers?” and “Why are we still developing new calibers? Isn’t there already a caliber for every job?”. The there are many answers to these questions, but for the sake of the length of this writing, I’m going to try to keep them limited to the “big ticket” items without going down too many rabbit holes.

Before we go too far, I’d like to make a clear distinction in terminology. While “caliber” is often used interchangeably with “cartridge”, that is not specifically correct. Caliber, in technical terms, simply refers to the diameter of the projectile, while the system of parts (case, projectile, powder, and primer) makes up a cartridge. This is perhaps a bit nit-picky, but it pays to be precise.

The first answer to the above questions is that shooters want more. At the same time, shooters want less. Obviously, this seems contradictory, so let me elaborate. Shooters want more energy delivered to the target. We want adequate energy delivered at longer ranges. We want less wind drift, we want less bullet drop (although, careful shooting practices can compensate for this), and we want less recoil. Manufacturers know this, and in their constant efforts to remain competitive, they attempt to offer cartridges to deliver. With this said, let’s get into what this actually looks like, and what encourages cartridge developers to keep innovating.

Safety and Function

One of the primary reasons for having so many cartridges, despite how similar they may appear, is for the safety of the shooter and the function of the firearm. Let’s use the Ford Mustang as an analogy. It was introduced in 1964, and every subsequent year saw small changes in design and features. Every few years, the Mustang was redesigned and looked like a different car, but still bore the Mustang name. No matter the changes, if a Ford said Mustang on it, it is accepted as such.

This type of iterative evolution, however, is not possible with firearm cartridges. This is because the firearms designed and manufactured for those cartridges only work with ammunition built to the same specification. For instance, .308 Winchester was debuted in 1952 by Winchester. In 1955, Winchester offered the .243 Winchester. This cartridge is very similar to the .308 in that it shares some components and is offered by the same company, and rifles of the same model can be chambered for either. But the two rounds cannot be shot in the same rifle. Now, imagine that Winchester had simply called the cartridge something like the “Winchester MultiPurpose”. In the ’52 models it would have a diameter of .308, and in ’55 would be necked down to .243. If both variants were simply called “Winchester MultiPurpose”, like the Mustang, then shooters would end up with ammunition that is not suitable for their firearms. Thus, whenever a cartridge is improved or otherwise changed, it is re-named and a new cartridge is born.

With that said, there are changes that can be made to a cartridge without the need for specifying a new one. For instance, powders have drastically improved since the introduction of the 30-06 in 1906. This has helped improve performance of the cartridge and allowed for improved projectile (bullet) shapes and velocities. It is a change in physical dimensions that necessitates the distinction of a new cartridge.  

Technological Limitations

The thing that drives the development for most new cartridges is overcoming technological hurdles. Of course, most of these new improvements come incrementally. For instance, in the late 1800’s, designers started to realize the drastic ballistic advantages provided by “pointy”, or spire point bullet designs. This came with another challenge: sharp pointed bullets end to end in tubular magazines ran the risk of setting off the cartridge loaded in front of it when the rifle recoiled. That meant stacking the cartridges. Shooters of the Mosin Nagant will know that stacking rimmed cartridges can lead to malfunctions, even in bolt action rifles, if careful attention is not paid during loading. Because of this, the “rimless” cartridge was developed, allowing a cartridge in the top of the magazine to be stripped from the magazine by the bolt without getting hung up on the round below it. This, in turn, made the idea of the semi-auto rifle even more appealing. Once again, every design improvement led to the creation of a new cartridge.

The Right Tool for the Job

Like any task, there are tools for a job, and there are the right tools for a job. Anyone that’s ever tried to fix a car with a pair of pliers and a Crescent wrench are familiar with this idea. Sure, you could clear out the wood chucks with your carry gun, or carry your .204 Ruger for self-defense, but you’d struggle to find anyone that would affirm your choices, even on the internet.

As our technology evolves, we can slowly refine our tools to be more specialized to their intended purpose. Of course, we can also try to strike a balance with a “versatile” rifle and cartridge, but versatile is synonymous in most cases with compromise. Many of us don’t have the required pocket depth to have a specific firearm and cartridge for each job, so we have to carefully choose which compromises we are comfortable with.

Compliance Cartridges

Simply put, compliance cartridges are those designed to comply with limitations imposed by some states for hunting purposes. For instance, the state of Kentucky allows hunters to use any center-fire cartridge. Michigan, on the other hand, requires (depending on zone) the use of a straight-walled cartridge with a case length between 1.16 and 1.80 inches, and greater than .35 caliber. This means your white tail classics like .243 Winchester, 308 Winchester, 30-06 Springfield, and the venerable 30-30 are out. These dimensions also rule out the smaller pistol cartridges like 9x19 and .45 ACP as they are too short, and those that are too long include the 45-70 Government and 38/55 Winchester.

This narrows the available cartridges significantly, and is precisely why the 350 Legend and 360 Buckhammer exist. One might be inclined to ask why these two particularly similar cartridges both exist and fill the same role. The answer to that question lies in hunter preferences. The 350 Legend is a rimless cartridge sharing a base with 223 Remington and designed to accept a .35 caliber projectile. This means that it will run nicely in bolt actions and semi-autos just fine. The Buckhammer, on the other hand, is a rimmed cartridge derived from the 30-30 straightened out to accept a .35 caliber bullet and designed to operate in lever action rifles. So, while these two cartridges seem like competitors, purchasers are primarily choosing which to use based on their preferred (or allowed) style of rifle.

Lifespan

One of the final, and perhaps most influential reason that there are so many cartridges is that it takes many years to phase them out. When a manufacturer introduces a rifle in a new chambering, that rifle may last years, with many still around from over 100 years ago. If the production numbers were great enough, and the chambering was popular enough, demand may continue long after the rifle goes out of production. So, since improvements never stop, and old designs stay relevant (because new rifles are expensive and old ones still shoot well), we have a piling up of cartridge designs, all with their own specifications, capabilities, manufacturers, and fans.

Classic vs Modern Comparison

One common frustration people have is that some new calibers seem to be redundant to their older counterparts. And in some cases, they’d be partially right. For example, the 243 Winchester introduced in 1955, and the 6mm Creedmoor, released in 2017. These cartridges have more similarities than differences in most cases. Generally speaking, these two cartridges could be chambered in the same rifles, with the same bolts and magazines. They use the same diameter bullets, and have very similar max pressures. For this discussion, I’ll be looking at load data from Hodgdon, where a 60k PSI max is used for both loads.

Generally speaking, the shooters of the 243 could look forward to using 55 grain projectiles for their varmint dispatching needs, and often up to around 90 grains for whitetail hunting. The 6mm Creedmoor can handle these projectiles as well. So, what’s the difference?

Primarily, there are some physical dimensional changes, but the major advantage lies in the twist rate. The 243 Win, when built to SAAMI spec, features a 1:10 twist rate, where the Creedmoor specifies 1:7.5. This allows the Creedmoor to stabilize heavier and longer bullets than the 243 Win, which comes with many advantages. You’ll easily find load data to use the longer bullets with the 243 Win, with minimal velocity difference between them. But, with the slower twist, the old faithful deer cartridge is limited to those in the 90-100 grain range. Some modern rifles chambered in 243 Win are shipping with 1:9 twist rates, but that is still a touch too slow for the longest bullets on the market today.

How much difference does this really make? Let’s use the 1000 ft/lb. standard for whitetail hunting. This means for an ethical shot, we’d like to have 1000 foot pounds of energy deliverable on the target. This isn’t a hard and fast rule, but a benchmark we can use to compare cartridges. In this case, the 243 Win, using a Hornady 90g ELD-X at a starting velocity of 3200 FPS, delivers this energy to about 425 yards. This shot might already be out of reach for many hunters, but at least we know that the energy is there. The Creedmoor on the other hand, using a 108g Berger Elite Hunter and starting at 3000 FPS, can deliver the benchmark energy all the way out to 625 yards. It’s likely that none of use will take a shot that long, but the illustration is clear. The longer bullet has added 200 yards to our effective range, despite the 243 Win having a 200 FPS head start.

The point of all this is not to argue the merits of the new or old cartridge, but goes to show that a technological change (aerodynamics in bullet design, changes in case shape) resulted in improved performance, and necessitated the creation of a new cartridge, no matter if it looks redundant on the surface or not.

Conclusion

The modern metallic cartridge with smokeless powder has only existed for around 130 years. During that time, we went from what essentially amounts to total ignorance in aerodynamics, to building airplanes that literally fly faster than rifle bullets. The continuous advancement in knowledge in these areas will mean continual improvement in bullet shapes, powder chemical makeup, rifle cutting methods, and others. New cartridges will continue being developed, and our capabilities as shooters will be ever so slightly better with each one. There’s no reason to be afraid of new cartridges, and no real reason to abandon the older ones every time a new variation debut. Just remember to save your brass.