Optimizing 9 mm Performance in Carbines
Article first appeared at NRAmedia.org
NRAmedia – Maker Bullets is a small and modest company in Atlanta, GA. Run by Paul Hendrixon, it isn’t a household name even through quite a few brands for which the company manufactures OEM ammunition and firearms parts are. This year, Maker Bullets is making a splash in clear ballistics-gel blocks with the introduction of three 9 mm cartridges designed specifically for pistol-caliber carbines. Available in 75-, 115- and 147-grain weights, the all-copper machined projectiles are teamed up with slower-than-usual powders to produce higher performance in 16-inch barrels. The choice to include the very light-for-caliber 75-grain bullet was made based on the observation that bullets lighter than 115 grains seemed more accurate in Kel-Tec Sub-2000 and other carbines I used for testing. Most of the firing was done with the Sub-2000, but Sterling, Beretta CX4 and AR-15 carbines all showed similar accuracy trends with various loads.
When the 9 mm cartridge was developed in 1902 by necking up 7.65 Luger, it was intended for short barrels. The original P08 had a barrel under 4 inches, and even the longest “artillery” model had less than 8 inches of barrel. The original 9 mm submachine gun, the MP-18, had less than 8 inches as well. As the cartridge popularity grew, many arms were chambered for it, but barrels have invariably stayed less than 10 inches in length. The increase to 16 inches typical of American semi-auto 9 mm carbines came as the popularity of submachine guns with non-institutional users collided into the 1934 NFA prohibition on barrels shorter than that without a tax stamp and an onerous, ATF slow-registration process. Combined with additional restrictions on actual submachine guns starting in 1986, NFA made it impractical to sell short 9 mm carbines, but didn’t affect the longer clones.
The longer barrels yielded less muzzle flash, but gave only a modest rise in velocity for the considerable increase in overall size. With the proliferation of pistol cartridges more deliberately optimized for compact carry pistols, the improvement in performance from carbine barrels got even more reduced. While carbines are usually overbuilt for 9 mm ballistics, they are, with the exception of MP5 clones and the SIG Sauer MPX, all simple blowback devices. Use of +P ammunition to improve performance can lead to early bolt opening, with potentially unsafe high-pressure gas escaping from the ejection port. Also, many of the 9 mm bullets are designed to work only within a narrow range of velocities, fragmenting and thus under-penetrating when launched too fast. People would still practice “cowboy logistics”, as Albert Yang called it, carrying a carbine that used the same magazine and ammunition as their pistol, but more for the increased accuracy than for hitting harder. I tested Maker Bullet ammunition along with several competitors to see if using two loads optimized separately for pistol and carbine would make sense.
First, the all-copper competition: Cor-Bon 115-grain DPX (1,380 fps, 3 MOA) and OATH 100-grain Tango (1,250 fps with the attendant low recoil, 2.6 MOA). Both give an extra 100 fps over service-size pistols. Accuracy is pretty good, considering most 124-grain loads group no better than 4 to 5 MOA. Both loads expand substantially and reliably. Winchester white box 115-grain FMJ (1,250 fps, 3 MOA) proved a solid plinking load, but with no velocity advantage over pistol. Shooting the Maker Bullet loads through a chronograph gave readings atypical of 9 mm ammunition: 1,500 fps for the 115-grain and a whopping 1850 fps for the 75-grain projectile. The 147-grain subsonic load predictably chugged along at 1050 fps. Designed for limited expansion, it opens up to only 0.6-inch but penetrates 16 inches in gel. Accuracy was pedestrian, around 4 MOA – probably adequate for ammunition designed for short-range engagements. The lighter loads really shined in that regard, each grouping around 2.5 MOA while expanding massively to a full inch and penetrating 16 and 12 inches, respectively.
The lighter load has flatter trajectory out to 500 yards, past which the heavier bullet makes more sense. Heavier ball has an overall kinetic energy advantage starting at 100 yards, with a 15 percent advantage on wind drift as well. Out of short pistol barrels, these loads perform poorly, with 1,010 fps (75-grain) and 900 fps (115-grain)—on par with .380 ACP. The bullets still expand but penetration drops to 6 to 8 inches. The lower-velocity impacts show that, with carbines, expansion stays constant out to nearly 100 yards, while penetration decreases gradually. The 75-grain bullet suffers just 20 inches of drop, roughly the height of a male torso, over a 150-yard range. A typical 115-grain FMJ making barely 1,250 fps at the muzzle drops a whopping 33 inches at the same range. In testing, these loads performed reliably in all carbines used and increased the hit probability on point targets like clays at distances past 25 yards by nearly 50 percent.
In sum, going to monolithic hollow-point bullets loaded over slow pistol powders extend the reach of the carbines just a little bit. The projectiles are impressively accurate, expand over a wide range of velocities and generate mild-feeling slow push instead of the abrupt jar I’d come to expect of blowback 9 mm carbines. With profiles approximating ball ammunition, they feed reliably in a variety of guns. Both loads still cycle in pistols, but with a prominent muzzle flash and relatively low velocity. If interchangeability of ammunition between carbine and sidearm is a priority, more mainstream ammunition would make more sense. If maximizing carbine performance is the goal, than these are terrific. In part because of relatively thin, whippy barrels, most 9 mm carbines change the point-of-impact considerably from load to load. If using Maker Bullet 115-grain for defense, you’d want to roughly match its trajectory for training. MI Bullet makes a non-ferrous (“Zuerillium”) non-expanding bullet with very similar external ballistics out to 150 yards and equally good accuracy.
Why go to such lengths to optimize 9 mm ammunition when rifle calibers are available? For urban shooters, it is about the availability of ranges—quite a few allow only pistol calibers. For the more budget-minded, it’s about inexpensive practice ammunition with high-performance defense options available. For the many users of the unique folding SUB-2000 carbine, it’s about wringing the greatest possible accuracy and terminal performance out of the weapon they already have and want to keep using.