Federal Premium Ammunition has invented a useful new cartridge for the AR-15 platform. The cartridge is essentially a 6.8 SPC case necked down to .224 caliber. The greater case volume provides higher velocities than the 5.56 NATO cartridge, and allows for heavier bullets, with better ballistic coefficients. Good idea. Unfortunately, Federal has decided to market the new round with, let’s just say, a very liberal interpretation of truth.
WORLD’S FIRST SUPERSONIC 1,300-YARD MSR 15 CARTRIDGE
Transform your MSR 15. Loaded with the 90-grain Gold Medal® Sierra® MatchKing®, all-new 224 Valkyrie provides less wind drift and drop than all other loads in its class and stays supersonic past 1,300 yards. The cartridge is the new choice for both long-range target shooters and hunters.
Unfortunately, that bullet does not actually stay supersonic past 1,300 yards.
With a muzzle velocity of 2700 fps, JBM Ballistics calculator gives the velocity at 1,300 yards for the 90 grain SMK (G1 BC of .563) as Mach 1.005, which is a hair above the speed of sound. That would seem to support the marketing claim of supersonic at 1,300 yards. Unless you know the difference between a G1 and a G7 ballistic coefficient.
When you do the same calculation using the G7 BC for the 90-grain SMK, you obtain more realistic numbers for terminal velocity. The G7 value for that round, as measured by Bryan Litz, is 0.257. Using that G7 BC, the 90-grain SMK crosses the sound barrier at about 1,085 yards (Mach 1.000). Then, at 1,300 yards, the Mach value is 0.898, which is well below the speed of sound.
Federal should have said “Supersonic past 1,000 yards”. That’s a benchmark attainable with an 18-inch barrel, rather than a 24-inch test barrel. Unfortunately, many websites have parroted the Federal marketing claim, making it seem like a universal truth. And I doubt that any of the commercial gun magazines have the stones to call out Federal Premium Ammo, as they spend a ton of money advertising in gun magazines, and have a lot of clout in the industry.
So, I guess gun blogs are good for something.