I’ll post this following discussion taken from the Frfrog website. As it contains no citations, the validity of the information cannot be established.
The theoretical maximum velocity attainable from normal commercial propellant powder and “conventional” loading densities is limited by the maximum velocity of expanding powder gases. Under ideal conditions this is stated as somewhere between 5700 f/s and 6000 f/s , and in conventional small arms between 4000-5000 f/s, by most authorities. Using specialized “solid propellants” the upper limit is theoretically about 13,000 f/s but at pressures way beyond practical.
Even under ideal laboratory conditions the maximum velocity attainable with standard propellant powders is limited by two factors: 1) A substantial portion of the energy derived from the burning powder is used up in accelerating the mass of gas behind the projectile, and 2) regardless of the amount of powder used energy transfer to the projectile can take place only at velocities that are less than the escape velocity of the propellant gases. Since the bullet cannot travel faster than the gases pushing it this sets a velocity ceiling. While raising pressures by burning huge amounts of powder can achieve some spectacular velocities there comes a point of diminishing returns, because most of the additional energy must be used to accelerate the greater mass of propellant gases produced.
Aberdeen Proving Ground reached close to 9000 f/s using a .60 cal smooth bore gun and using 720 gr (!!) of IMR 4895 and a 113 gr projectile and they believed that the theoretical maximum velocity in that “gun” would be about 10,000 f/s. The all time record for a conventional solid propellant gun (as opposed to light gas guns, etc.) is believed to be held by the people at the Canadian Armament Research and Development Establishment (CARDE). In the early 1960s they used an 81.3mm smoothbore gun with a 95 caliber length barrel to reach the blistering muzzle velocity of 9154 f/s but I don’t have any information on the projectile or the type of powder used. (A velocity of 9153 feet per second was supposedly achieved in 1938 by a German experimenter named Langweiler, firing a special 8 mm round using a 1 meter (39") barrel. The bullet weighed about 3.85 gr and the propelling charge was 170 gr of an unspecified powder designed to give a larger burning surface to the grains. The maximum pressure in the gun was listed as 176,500 psi. The reported velocity is generally considered suspect due to the limitations of the powder gas velocities and to the primitive velocity recording done via a ballistic pendulum.)
In more conventional firearms the .220 Swift is capable of launching a 40 gr bullet at around 4380 f/s from a 26 inch barrel which is fast in anyone’s book and is probably the “commercial” rifle ammunition record. In handguns, velocities close to 3000 f/s have been achieved using a single shot pistol with such commercial rounds as the .222 Remington and 40 gr bullets, but I’m sure that someone out there has chambered a Contender in .220 Swift or something equally insane.
Some rifle experimenters have reported velocities around 5300 f/s using huge powder charges and light weight bullets. One example was a .378 Weatherby necked to .30 caliber and firing a 30 gr “pellet.” Reportedly projectiles of down to about 3 gr were also used. As you might expect the barrel only lasted for a couple of shots. Another cartridge known as the .316 (some sources say “.416”) Gerlich (designed in the late 1930s by Hermann Gerlich) is reported to have achieved 5,325 f/s from a 34 inch barrel with a 118 grain bullet on top of 146 grains(!) of IMR4895 and ordnance test reports indicate that velocities of up to about 5700 f/s may have been achieved using a squeeze bore design in which the bullet starts out at one diameter and is squeezed down to a smaller diameter at the muzzle. Most of the Gerlich rounds used a bullet that started out at .316" and exited the muzzle at .240".
For non conventional “firearms,” laboratory devices utilizing exotic gases or large charges of conventional powders as a propellant, and evacuated bores and target chambers have yielded velocities of 25,000 f/s and higher using projectiles as heavy as 237 gr and a 20 foot long evacuated bore and target chamber. (The August 2003 American Rifleman had an interesting article on these “guns.”) Electromagnetic “rail guns” have also been achieving very high velocities, up to 26,000 f/s or more, using projectiles weighing up to 160 gr. In a more practical vein The US Army’s “Miramar Gun B” rail gun fired a 2.30 lb projectile at over 11,150 f/s, at sea level in the atmosphere and that was only at about 80 percent of capacity. I’ll leave it to you to figure out the KE.
In 2007 BAE Systems delivered a 32 megajoule launcher to the Office of Naval Research (ONR) Electromagnetic Launch Facility. On 31 January 2008, test firing began with this launcher. The rail gun was fired at 10.64MJ (megajoules) and the 7 lbs. (3.2 kg) test slug projectile attained a muzzle velocity of 8,268 fps (2,520 mps). In 2010 the same gun was successfully fired at 33 MJ and the 40 pound projectile reached a reported 8500 fs. This equates to some 445 million ft lb if I did the math right. They are supposedly working on a 60+ megajoule gun that should come close to doubling the velocity.
The practical velocity championship for current “working” ammunition should probably go to either the M829 APFSDS-T (Armor Piercing Fin Stabilized Discarding Sabot-Tracer) 120mm rounds as fired by the M1 Abrams tank, or to the Soviet equivalents. The original M829 threw a 9.41 pound (that’s 65,870 grains), 1.06" diameter, 24" long, depleted uranium dart at 5480 f/s! The A1 version fired a 10.78 pound dart at 5170 f/s and the current A2 version throws a slightly longer (30") but skinnier (.8") 10.85 pound dart at 5512 f/s. (For you hand loaders, operating pressures of the M829 series are between 74K psi and 96K psi.) The M865 TPCSDS-T (Target Practice Cone Stabilized Discarding Sabot with Tracer) training round throws a 7 pound aluminum dart at 5577 f/s. (This round has a MUCH shorter maximum range than the M829 and can thus be safely fired on most tank ranges.) There is also a new US M829A3 round that reportedly launches a 22.2 pound (!) dart at 5200+ f/s although velocities as high as 5600 f/s have been reported in some publications. (Even at "only "5200 f/s that’s 9.2 MILLION foot-pounds of KE!)
The Russian 125 mm equivalents of the US rounds reportedly launch their projectiles at close to 5900 f/s but their terminal performance is still inferior to the US rounds. Several years ago the Ukrainians showed off a prototype of a longer 125mm gun, called Vitiaz, and it reportedly launches its 5 kg projectile at 6660 f/s but these specifications are not verified and are suspect.