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.17 Hornady Mach 2
Left: .17 HM2, Right: .17 HMR
Type	Rimfire
Place of origin	United States
Production history
Designer	Hornady
Designed	2004
Manufacturer	CCI/Hornady/Eley
Produced	2004–Present
Specifications
Parent case	.22 Long Rifle
Bullet diameter	.172 in (4.4 mm)
Neck diameter	.180 in (4.6 mm)
Shoulder diameter	.226 in (5.7 mm)
Base diameter	.226 in (5.7 mm)
Rim diameter	.275 in (7.0 mm)
Case length	.714 in (18.1 mm)
Overall length	1.00 in (25 mm)
Primer type	Rimfire
Ballistic performance
Bullet mass/type Velocity Energy 17 gr (1 g) V-Max 2,100 ft/s (640 m/s) 166 ft⋅lbf (225 J)
Source(s): Hornady

The .17 Hornady Mach 2, or .17 HM2, is a rimfire cartridge introduced in 2004 by the ammunition manufacturer Hornady, following the successful launch in 2002 of the .17 HMR. The .17 HM2 is based on the .22 Long Rifle "Stinger" case, necked down to .17 caliber (4.5 mm) and using a bullet weighing less than half what typical .22 Long Rifle bullets weigh.

Performance

The ultralight bullet is a key part of achieving the very-high velocity for a rimfire round. It weighs only 17 grains (1.10 g) vs 30-40 grains (1.94-2.59 g) for typical .22 LR bullets. The .17 HM2 may or may not live up to its "Mach 2" name, depending on geographic location and conditions, with velocities out of a rifle of 2100 ft/s (640 m/s). The velocity is nearly double that of a standard .22 LR, which results in a much flatter trajectory out to the 175 yards (160 m) effective range of the cartridge.

Converting rifles

Since the .17 HM2 is based on the .22 Long Rifle converting most bolt action firearms chambered in .22 Long Rifle to .17 HM2 requires only a barrel change. The higher pressure makes conversion of semi-automatic firearms more difficult, as virtually all are blowback designs that are sensitive to pressure changes. Kits for the Ruger 10/22 and AR-15 platform have appeared, and they replace the factory bolt or bolt handle with a heavier one to increase the bolt mass and compensate for the higher pressure.

See also

• List of handgun cartridges
• List of rifle cartridges
• Table of handgun and rifle cartridges
• 4 mm caliber
• .17 Rimfire

References

• "The .17 HM2" by Chuck Hawks

1. Hornady Manufacturing Company :: Ammunition :: Rimfire :: 17 Mach2 :: 17 Mach2® 17 gr V-MAX®
2. The Borchardt Rifle Corp. sells parts to convert Ruger revolvers to .17 HM2.

External links

• Eley
• CCI

v t e Cartridges with bullet diameter between 4 mm (0.16 in) and 5 mm (0.20 in)
Rimfire cartridges	.17 Mach 2 .17 HMR .17 PMC/Aguila .17 Winchester Super Magnum 4.5×26mm MKR 4mm M20
Centerfire cartridges	Pistol, carbine and PDW cartridges 4.25mm Liliput 4.38×30mm Libra 4.5×40mmR 4.6×30mm HK Revolver cartridges .17 Bumble Bee Rifle cartridges .17 Hornet .17 Mach IV .17 Remington .17 Remington Fireball .17 Ackley Bee 4.6×36mm 4.85×49mm

• Pistol and rifle cartridges
• Rimfire cartridges
• 2004 introductions