If you have not heard of them before, The Ballistics By The Inch project tests cartridges by shooting them through a rifle-length barrel, noting the velocity, then cutting an inch off the end of the barrel and repeating until the barrel is just 2″ in length. This provides valuable information because the velocity published by ammunition companies come from measurements through a long test barrel. For example .22 Magnum bullets are usually tested by the manufacturer with a 24″ barrel. Nobody these days shooting .22 Magnum with a 24″ barrel, and the .22 Magnum has a growing following among revolver and pistol shooters who are shooting with 4″ or shorter barrel.
The BBTI project have just published their tests of the .22 Magnum with barrel length ranging from 19″ to 2″. They have also tested the cartridge in a number of real-world guns.
Looking at these figures, I have to wonder if there is any point in owning a snub-nosed revolver or derringer in .22 Magnum instead of .22 Long Rifle, since the velocity/energy is going to be the same. The only “advantage” is a bigger fireball.