The .17 HMR
 

Nation	Year	Max. press.
U.S.A.	2002

    As with the 22 rimfire, there is no load data for this cartridge, because there is no reloading it. This is a pretty recent round, is the latest successful rimfire round, and is one of only two rimfire rounds which have earned the distinction of "Magnum", the other being the 22 magnum. The last successful rimfire round to be introduces was the 22 Magnum back in 1960. These are rimfire rounds and have no primer as such. The brass is thin and easily crushed, so a liquid primer material is sprayed or dripped, and then spun directly into the rim of the case.
    This little round reminds me of nothing so much as a scaled down .223 round. By coincidence, the muzzle velocity, of 2525 fps, is about the same as that of the .223 round. This is a rare example, perhaps the only successful example to date, of a bottle necked revolver cartridge. This has been tried in the past, notably with the 22 Jet, and found wanting. The problem has generally been with the headspacing. This may not be much of a problem with the .17, because of it's rimfire ignition system, and low bullet weight. 
    The bullet diameter is about the same as that of a pellet gun, and it's weight is about double that of the standard .177 pellet. It's velocity is, however, nearly triple that of the air rifle pellet. The photo above, shows the 17 alongside of a pellet, for comparison purposes. Hornady has also introduced their 17 Mach2, which is essentially a 22 long rifle necked down for a 17 caliber bullet. The Mach2 has a muzzle velocity of 2100 fps, and is not interchangeable with the 17 HMR. These are designated as rifle rounds, and the velocity figures given are out of 16" rifle barrels. The actual velocity out of a handgun is probably more like 2100 fps for the magnum, and something like 1700 fps for the Mach2. I will be doing some chronographs this fall, and will update this page accordingly.
    Often, things do not happen quickly in firearms development. As with the 357 magnum, and the 44 magnum, introduction of the 17 hmr had it's root in experiments done by intrepid handloaders, years before the introduction of the cartridge itself. Versions of the 17 rimfire magnum, with 20 grain bullets at 2700 fps, were being played with as far back as 1992.
    This new little round has generated quite a bit of enthusiasm, to the extent that it has it's own web site at http://17hmr.net/index.htm . The best single review that I have read of this ammunition is at Varmint Al's site at  http://www.varmintal.com/17hmr.htm  .