| .17 Mach IV | |
| Origin: | United States |
| Type: | Rifle |
| Designer: | Vern O Brien |
| Design Date: | 1962 |
| Parent: | .221 Remington Fireball |
| Case Type: | rimless bottlenecked |
| Bullet: | .172 |
| Neck: | .206 |
| Shoulder: | .361 |
| Base: | .378 |
| Rim Dia: | .378 |
| Rim Thick: | .045 |
| Case Length: | 1.400 |
| Length: | 1.830 |
| Rifling: | 1 in |
| Primer: | Small Rifle |
| Bw2: | 25 |
| Btype2: | HP |
| Vel2: | 3680 |
| En2: | 797 |
| Bw3: | 25 |
| Btype3: | HP |
| Vel3: | 3890 |
| En3: | 849 |
| Balsrc: | 6mmBR[1] Hodgdon[2] |
The .17 Mach IV / 4.4x35mm is a wildcat centerfire rifle cartridge, based on the .221 Remington Fireball case, necked down to fire a 0.172inches bullet. The cartridge was introduced in 1962 by Vern O’Brien.[1] The cartridge offered an easy case conversion and good ballistics, but could not compete against the .17 Remington.[3]
The name, Mach IV, comes from the claim that the bullets can reach 4000ft/s.[4] Due to the relatively small case capacity, even small variations in powder of 0.5gr can lead to the difference between a safe and dangerously over pressure load. Aftermarket barrels for the XP-100 pistol were sometimes marked ".17 Mach III" due to the lower velocity produced by the shorter barrel.[5]
The .17 Mach IV became very popular with varmint hunters, so much so that in 2007, Remington introduced its own very similar version, the .17 Remington Fireball.