The operating crew was given access to a small range of 75x714mm.R (75mm) ammunition options for the specific action at hand. This included the standard 15lb AP (Armored-Piercing) round as well as the 9lb AP40 which featured a tungsten-based core, ultimately proving a rarity as the war progressed. Even out to 2,190 yards, the AP40 (also known as "APCR" = "Armor-Piercing, Composite Rigid") projectile could pierce some 98mm of armor and, as can be imagined, this penetration value (up to 154mm) was only heightened at closer ranges making the PaK 40 one of the more feared - and respected - of the German guns. Of course there was also the standard issue 12.6lb HE (High-Explosive) rounds to deal with infantry and structures. Muzzle velocity of the AP, AP40 and HE projectiles were listed as 2,650 ft/s, 3,300 ft/s and 1,850 ft/s respectively. Effective range of the AP round was out to 8,350 feet while the HE round was rated effective out to 25,350 feet. PaK 40 projectiles were the same standardized rounds utilized by the long-barreled KwK 40 series tank guns fielded by Panzers, being differentiated only by their cartridge cases.
From the outset, the PaK 40 proved an excellent anti-tank weapon system - however, her excellence ultimately relied on the professionalism and training of her firing crew as any weapon was only good as the man behind it. At any rate, the PaK 40 was more than capable of penetrating the armor facings of any Allied tank at the time of her inception. However, if there was a key drawback in her design it was in her weight - her wheels regularly battling the high mud of the terrible Russian winter and forcing the use of artillery tractors to transport her about. In the German retreat of 1943, many PaK 40s were simply deserted along roads and passes by their German Army owners due to their immobility and getting stuck in mud and snow. Combat also brought the PaK 40 to battles in Italy and across the Mediterranean region.
The PaK 40 would see production through to the end of the war, remaining largely unchanged from her original form - such was her excellent design and general battlefield usefulness, plus Germany was fighting an all-out defensive war by the end. In all, over 23,000 PaK 40 guns were produced out of German-held factories with 11,728 of these produced in 1944 alone. The PaK 40 was in action until the final days of the war, still deemed capable of "addressing" most enemy tanks as needed.
The PaK 40 formed the basis of a few other notable developments including a dedicated tank-based main gun and a lighter version specifically designed for use on ground-attack aircraft. The split trail carriage was also the mount for an improvised infantry gun mounting a short-barrel 75mm gun. The PaK 40 was utilized as a field gun under the designation of 7.5cm FK 40 "Feldkanone". The PaK 40 became the primary armament on tracked vehicles to form stopgap "Marder" tank destroyers and fitted to 8x8 armored reconnaissance cars and halftrack carriers for infantry fire support duties and stand-off tank destroyers. Some 6,000 PaK 40 series guns were fitted to vehicles in these manners.
The PaK 40 was utilized beyond the German Army during World War 2, with operators including allies (some by force) such as Albania, Bulgaria, Czechoslovakia, Finland, Norway, Hungary and Romania. The Soviet Army even utilized captured PaK 40s (a common practice by both sides) against their former owners, in a way informally paying "respect" to the German design. Norway retained a stock of PaK 40s in their army inventory for a time during the post-war years.
Incidentally, the acronym of "PaK" stands for "PanzerAbwehrKanone".