Things in the cartridge world are changing, for sure. In the last decade, we've seen cartridges get smaller, bullets get longer and the overall mentality change. So, what's the deal? Exactly what is the mind set? Let's take a look at some of the modern cartridge developments and the school of thought.
The modern family of cartridges began - sort of - with the 6.5 Creedmoor. Some are sick of hearing about its virtues, and some are completely unfamiliar with the design. Nonetheless, it is a sound design, even if its father has faded into obscurity, but I believe we should begin with this cartridge. Based on the .30 T/C (which in turn was purported to give true .30-06 Springfield velocities from a short-action cartridge) the 6.5 Creedmoor filled a niche: it delivered an unprecedented trajectory from a cartridge that fit into the AR-15 magazine. Once the shooting world saw how well the Hornady-developed cartridge performed in the gas guns, it was no time before the cartridge made its way into the bolt guns. Accuracy was fantastic, and the twist rate that was the usual offering for the 6.5mm cartridges gave amazing performance downrange; the Sectional Density (S.D.) and Ballistic Coefficient (B.C.) of the 6.5s are unparalleled.
Now, let me say this: the 6.5 Creedmoor is no miracle wrought in brass; the formula has been with us since the 19th century in the guise of the 6.5x55 Swedish Mauser and 6.5x54 Mannlicher-Schoenauer. From the inception of the bore diameter, the twist rate has been one which would handle the 156- and 160-grain bullets, which are both very long for caliber, and in modern bullet profiles will offer an excellent B.C. Compare those bullets to those suitable for the .270 Winchester, and you'll find a definite advantage. It has nothing to do with the .270's case capacity, but all to do with the .270's twist rate.
The beauty of the Creedmoor - and the Swede and 6.5-284 Norma - is the lack of recoil combined with the excellent downrange performance. Wind deflection values are low; the bullets retain all sorts of energy downrange and their S.D. values give good penetration on game animals. It is therefore the desirable bullet shape, and not the horsepower of the cartridge, that makes the Creedmoor what it is.
The low-recoil, long bullet combination was once again utilized for the 6mm Creedmoor - sort of obvious, considering that case was simply necked down to hold 6mm bullets - as well as in both the .22 Nosler and .224 Valkyrie. Again, these new cartridges were designed with the AR-magazine as a limiting factor for overall length, and thereby requiring a shorter case in order to leave room for the long, high-B.C. bullets. As far as downrange performance goes, the moderate velocities of these cartridges - at least when compared to some of the magnum cartridges - aren't really a handicap, as the milder cartridge, when mated with the sleek bullets, give the shooter hours at the range without pounding the shoulder to dust.
For distances out to or exceeding 1,000 yards, the quartet of cartridges I've mentioned most certainly get the job done, but aren't there designs which would do a bit better job, even if the recoil did increase a bit? Well, the answer is both yes and no. I know that the .22-250 that has served me so well over the years would launch even the 100-grain bullets better than the .22 Nosler or the .224 Valkyrie, but it's got a couple things holding it back. One, the twist rate in modern .22-250 rifles is 1:12 at best, and that has a hard time stabilizing anything heavier than 60-grain bullets. Two, even with the proper twist rate in the barrel, to properly seat the truly long bullets that give the long-range performance, you'd have issues with the magazine length of most of the rifles on the market today.
Even the .300 Winchester Magnum - capable of great velocity and hair-splitting accuracy - has problems using the .30-caliber bullets with the highest B.C. values and maintaining the prescribed overall length that allows the cartridge to function properly in the magazine. The bullets would be seated so that the case mouth was on the bullet ogive, rather than the shank of the bullet; and that doesn't work at all. So, in order to take full advantage of the longer, sleeker bullet, the overall length of the cartridge must be violated. Even the 6.5-284 Norma - that darling of the long range community - works much better in a long-action rifle than the short-action that it was designed for. The additional magazine space allows the shooter to seat bullets farther out of the case, without compromising case capacity. Long-range bullets, with the long ogives and boat tails pose no issue if the longer action is used. Hence, these recently developed shorter cartridges - designed around the longer bullets, instead of vice versa -have started a trend that I feel will be with us for some time.
The 6.5 PRC - based on the .300 Ruger Compact Magnum - is a fatter, faster design, but adheres to the short case/long bullet theory. It will better the trajectory of the Creedmoor, but at the price of additional recoil, and can be considered the magnum version of the Creedmoor theory. The short powder column seems to enhance accuracy - the PPC cartridges were glaring example of this - but this design seems to be free of the feeding issues that the Winchester Short Magnums all-too-often exhibit.
Norma's new .338 Norma Magnum is another example of the shortened cartridge theory; they took a .338 Lapua - itself based on the .416 Rigby - and shortened the case to the same length as the .30-06 Springfield, not to give a shorter overall length than the Lapua, but to better handle the longer ogive bullets in a magnum-length magazine. The .338 Norma's case capacity is slightly reduced in comparison to the Lapua - roughly 6 to 7 percent - but the pressure is ramped up a bit to meet or beat the Lapua's velocities. I've shot them both, and I like them both, but the .338 Norma Magnum makes it a bit easier to seat the longest .338-inch bullets, and it is seriously accurate.
Again, please realize these new designs haven't set any velocity records, and that they don't generate ridiculous energies. As far as hunting rounds go, you can get the Creedmoor's performance out of the 6.5x55 Swede, or the 6mm Creedmoor's performance from the .243 Winchester in a bolt-action rifle, with little trouble, but if the AR-platform is your thing, it should be obvious that the Creedmoor was designed for that exact purpose. At sane hunting ranges, you probably won't see any huge advantage to these new designs, but then again they were all designed as long range specialty tools.
With the popularity of long range shooting competitions, you'll see more cartridges designed with these parameters in mind, taking full advantage of the longer bullets that are popping up like spring grass. It's a good thing, as they obviously do their job, and do it well.