Miniature Varminter: The .17 Mach IV
By Chuck Hawks
The O'Brien Rifle Company introduced this hot little varmint cartridge in the mid 1960's. It is based on the .221 Fireball case necked down to accept .172" diameter bullets.
Like most wildcat .17's, the 1971 introduction of the .17 Remington put the .17 Mach IV on the skids. The later introduction of the .17 Remington Fireball, also based on the .221 case and very similar to the .17 Mach IV, pretty much finished the job. The .17 Rem. Fireball has a slightly longer case body and a shorter neck for slightly greater powder capacity. Today, you don't hear much about the .17 Mach IV, although it is still included in the latest Hornady reloading manual.
Regardless, the .17 Mach IV is a cute little cartridge designed for very short action rifles. Its diminutive case is only 1.40" long, and the Maximum COL is 1.77". The .221's 23-degree shoulder was sharpened to 30-degrees for the Mach IV case, which seems like a pointless complication to the case forming operation.
Hornady has long offered two bullet weights in .172 caliber to reloaders, 20 and 25 grains. They suggest the 20 grain bullet at up to 4000 fps for smaller varmints and a 25 grain bullet for larger varmints, such as ground hogs or coyotes, and windy days.
The 9th edition of the Hornady Handbook of Cartridge Reloading points out that, as with any very small case and light bullet, small changes in powder charge make large differences in pressure and velocity. A reasonable starting load would be 14.1 grains of H4198 powder behind a 25 grain Hornady V-MAX bullet for a MV of 3400 fps. A maximum load of 15.6 grains of H4198 is good for a MV of 3700 fps with that bullet. These Hornady loads used reformed Remington brass and Remington 7-1/2 primers and were tested in a T/C Encore rifle with a 24" barrel.
Because it burns a small amount of fast powder, the .17 Mach IV is a relatively quiet centerfire cartridge, noticeably more so than the .17 Rem. or the .223 Rem. Recoil is very light. The small volume of powder also means that it does not foul its barrel as quickly as the bigger case .17s.
These factors, along with a MV in the 4000 fps range, made me think that the .17 Mach IV deserved more popularity than it got. Apparently Remington thought the same when they introduced the factory equivalent in the form of the .17 Rem. Fireball. Hornady recently sealed the deal with the introduction of the even cuter, smaller and quieter .17 Hornet.
Copyright 2005, 2014 by Chuck Hawks. All rights reserved.