Here’s a short retrospect on what’s set the standards for most new cartridge designs, and why… KEEP READING
I’m not an engineer, but, like all of us, we rely on those folks to develop just about all the things we have and use. When we look at a new development, one that’s proven to work better than the “old” way, sometimes it’s easy enough to understand why. Cartridge development over the years is a good example.
What makes a good cartridge? Answers, of course, vary with the intended use, the performance needs. For the most part, power (which mostly is velocity), and “efficiency” (which is essentially getting the most from the least amount of propellant, likewise increasing barrel life), and accuracy (always) top the list. And, to me, “accuracy” is a combination of small group sizes and, even more, small group sizes all the time! Consistency.
Case capacity has the most to do with the first: more room for gunpowder means more power. Also, it’s pretty clear that pressures have been going up! There’s a big (big) difference in the pressure levels of some of the “new” cartridges compared to the older, longer-lived rounds. Sometimes it’s not because the older round can’t “take” the additional pressure, it’s because the guns might not. A round developed turn-of-the-century fits a rifle from the same era. Well, steel has improved, manufacturing has improved, and, some no doubt, is that the trend toward “shorter, fatter” cartridge cases also contributes.
So. About that…
In my mind, and certainly in my “world,” which is competitive shooting, one of the most influential cartridges has been, and still is, the PPC. That was developed in 1975 by Ferris Pendell and Dr. Lou Palmisano (hence “Pendell, Palmisano Cartridge”), and the idea was to design the “world’s most accurate cartridge.” They did. It has the record to prove it. However, that’s in Benchrest (capital “B” meaning formal competition). Bechrest is nearly always a 100-yard event. The idea behind the PPC wasn’t to set the range on fire with excessive velocity, although it’s well more rapid than others then popular in that game. The idea was to improve cartridge structure to improve shot-to-shot consistency, and another part of that plan was to extend the duration of load-to-load consistency by slowing down firing-induced changes to the case. It’s native caliber is 6mm (.243).
(By the way, the PPC is based on .220 Russian, which is still how many get their brass: fire form it from that. That round is associated with 7.62X39mm, which came earlier and was based on the WWII German 7.92x33mm Kurz, the Mittelpatrone.)
A few reasons, offered by its creators, why PPC shoots so well: One, it’s a short case, a scant 1.515 inches overall. That makes it more rigid and less susceptible to warp. It also means it fits into a short action, also more rigid (and with shorter bolt travel). The case neck is relatively long, which means the entire shank of the bullet is within the neck, never below it. That means no influence from varying cartridge wall thicknesses (the case neck walls can be made near-perfectly consistent), avoiding the case neck “donut” at the neck, shoulder juncture. Its body area diameter is 0.440-vicinity, which is (was) a good deal larger than the more common 0.378 commonly used in Benchrest. Case shoulder is 30-degrees.
About that: Well before the PPC there was P.O. Ackley. Well-known for his “Ackley Improved” rounds, which, pretty much, were standard rounds with a sharper shoulder angle. In sharpening (flattening) the shoulder angle (usually from 23-degrees to 30 or even 40), that also elevated the shoulder, and that increased case volume. More speed! Another benefit of the sharper shoulder was a notable reduction in the “flow” of the brass. That meant less change firing to firing. The sharper angle on the shoulder essentially “caps” the flow in that area.
Other attributes engineered into the PPC have and haven’t been incorporated into subsequent new cartridges. Notable is the smaller-than-standard flash hole. This requires a likewise smaller sizing die decapping pin. Also, PPC uses a small rifle primer, which is fitting based on its overall round size. Over years, there have been retro-engineered common rounds with small primer pockets and those have worked well. For a spell, over the time it was available, small-primer .308 Win. brass found great favor among competitive shooters. Remington made it. Interestingly (again from a perspective of one who isn’t an engineer) pressures were higher compared to standard loads based on routine large-primer brass. Velocities tended to be more consistent.
Another reason for PPC perfomance is one I don’t pretend to understand, and that is its “efficiency.” That’s all in the science of internal ballistics and I only can attest to its influence. I have been a PPC user (the 22 variant) for a good while. It’s what my main NRA High Power Match Rifle is chambered in (AR15 platform). From virtually the same amount of the same propellant, there’s a solid +100 fps gain over the .223 Rem. The structure of the PPC indeed “works.” From that, and from “those” (High Power shooters), rapidly evolved experimental takes on the essential PPC.
Moving on, rounds like 6BR and 6.5 Grendel are outgrowths of the PPC format (“upgrowths” actually: they’re bigger capacity). We’ve also seen the essential influence in the popular 6.5 Creedmoor and the 6XC, which currently dominate competitive across-the-course and long-range shooting (“standard” long range, not the 2-mile stuff, that would be .375 Cheytak…).
Looking at semi-auto developments, many of which have been coming at us fast and furious, it’s clear cartridge developers are exploiting these same ideas. There is a (short) limit on what will fit into an AR15 upper receiver, for instance, because, one, it’s a finite amount of space, of course, and, two, there’s a magazine box, and these are related. More power in this platform means a fat case.
Now. I am in no way suggesting anyone run out and tool up for PPC in the next rifle! It can be soundly beaten in the “real world” of our needs from a cartridge. There are similar rounds with more velocity, easier availability, lower cost, and on down the list of desirables. In the next couple of issues, I plan to talk more about some of the newest rounds, but wanted to offer just a little retrospect on where it all came from before getting into where it’s gone!
This article was adapted from content in Glen’s newest book: America’s Gun: The Practical AR15. Go check it out HERE!
Check out AckleyImproved.com