Shooting across the sky like a comet came the Marlin Mach 2. This handy little .17HM2 caliber semi-auto had fun written all over it. Yet just as soon as it appeared, just like a comet, it raced away and vanished. Yes, we said .17HM2, not .17HMR When the .17HMR was introduced in 2002, it was hailed as the greatest single small caliber round since the .22 Magnum. The thing is, it was just a little too much for lighter-made rifles to handle. This led to the .17 caliber Hornady Mach 2, commonly just called the .17HM2 in 2004. (the 17M2 compared to a normal .22LR on the right) This round was a .22LR Stinger that was necked down and, instead of having a 36-grain lead bullet, was given a 17-grain .17-caliber ultralight pointed round attached to it. Since the round ran over 2100fps, it was called the \'Mach 2\' to differentiate it from its taller and barely older brother. Technically this is incorrect as the speed of sound at sea level is 1116.43701 fps, but \'Mach 2\' is way catchier that \'Mach 1.8809\' (The .17M2, left, is a much smaller round than the better known .17HMR, right) This short sized round could deliver .22 magnum-like performances (166ft/lbs of energy downrange) from a rifle that was originally designed to shoot a .22LR. All that was needed, in theory, was a .22LR rifle that was given a new, .17-caliber barrel and chamber to fire it. Design (The Marlin 795, seen here and still in production as a .22LR with Marlin, was the basis of the short-lived M717M2) Marlin came out with their Model 717M2 (with the M2 standing for Mach 2) in 2005 to capitalize on this new round. Built from lessons learned in its millions of Model 60, 70, and 795 .22LR rifles, the new gun was based heavily upon these. Like the 795, the new 717M2 included an automatic \"last-shot\" bolt hold-open feature, a manual bolt hold-open and a cross-bolt safety. It had a micro-groove rifled barrel, worked through blow-back autoloading, and ejected spent rounds to the side while loading new ones from a simple single-stack 7-shot detachable box magazine. We aren\'t sure, but we are almost certain that it\'s the very same mag as the 795 used. The resulting 717M2 was handy, with an 18-inch barrel giving it a 37-inch overall length on its Monte Carlo-style hardwood stock. The receiver itself had been reworked to give it a heavier bolt to absorb the increased pressure form the Mach 2, which gave it a very 1960s Cadillac styling to its rear. A 2005 Shooting Times review mentioned that the gun fired flawlessly. The *average* group that the field reporters found at 50-yards was 0.65-inches, with several going smaller. The little 17HM2 clocked 1996fps out of the Marlin\'s 18-inch barrel. One odd thing was reported though; the stock had to be replaced due to cracks... Ruptures, cracks, and problems It seems that the chamber pressure of the very zippy .17HM2 proved too much for what was basically an upgraded .22 platform. All one has to do is Google \"Marlin 717M2 broken stock\" to find dozens of pages where owners of these guns have experienced cracked stocks after case ruptures. Typically, there were no injuries by the shooters in these incidents but they usually blew out the plastic trigger guard plate, and split the stock and the handguard. With these issues out there, it was not surprising that Marlin shuttered the line on the 717M2 by 2009. Today, Marlin (now part of Remington and operating in a new factory in Kentucky rather than the old New Haven CT works), is very slim on their .17HMR offerings. They have the XT-17 bolt action, itself a rechambered version of their XT-22 rifles. With the locked breech of the XT\'s, bolt ensuring that the extra pressure from the hot little HMR goes downrange and not out and about, these guns are likely inherently stronger than the forgotten 717M2. Marlin currently offer no (zero) guns chambered in .17HM2 today. Getting your own These guns pop up on sites like Gunbroker and Armslist anywhere from $200-$350, usually with optics already installed on the more expensive end. Be sure to check for cracks in the stock around the rear of the action and pistol grip area. Since it\'s a model that was only around for a brief minute in time, and takes an oddball round, it\'s very possible that these guns will be collectable in years to come. Therefore, an investment of a couple bills into one of these guns that is still in 97% plus condition could be a smart twenty years from now. If you come across one in less than that shape, but is still a shooter, shoot it up. These guns are laser-like accurate well out to 100-yards and make great squirrel guns and popcan assassination rifles. Be sure to stock up on rounds, as its conceivable that Hornady will stop production of them as no maker is chambering rifles for this load anymore. Moreover, as with any firearm, be sure to use standard pressure factory new ammunition along with eye protection and ear protection when shooting.