Although 9mm Luger was originally designed for a handgun, wide use in submachine guns and carbines lead to the use of slower powders optimized for an approximately 8in barrel length. Using standard defensive ammunition in subcompact pistols with short barrels causes excessive muzzle flash, a louder report due to higher pressure at the muzzle, and reduced velocity. At the most extreme, a 75gr hypervelocity load (from another manufacturer) optimized for carbines produced 1,850fps from a 16″ barrel but only 950fps from a 4″ pistol! Lower than expected velocity also affects expansion, with partial bullet mushrooming reducing terminal performance.
Ammunition optimized for subcompact handguns performs well in full size pistols but not in carbines. Besides the faster powders, an optimized cartridges also use different bullets. All-copper projectiles with machined expansion cuts open properly even at slightly reduced velocities while retaining, unlike softer lead JHPs, competent performance against windshields and other intermediate barriers. Using copper, modern machining techniques can craft a far more complex cavity than is possible with jacketed lead. This means that the size of an unexpanded hollow point can be kept small enough to facilitate reliable feeding.
The Steinel 124gr subcompact load delivers a 2/3in expansion with the muzzle velocity around 960fps: the subsonic projectile doesn’t generate a shockwave, and the muzzle blast is less severe than with a non-optimized round. Less flash — better follow-up shot accuracy and situation awareness. This ammo can be used with full-size handguns as well.