From Shooting Illustrated: http://www.shootingillustrated.com/articles/2016/2/18/optimizing-9-mm-performance-in-carbines/
by Oleg Volk
Thursday, February 18, 2016
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.