.17 HM2

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 the weight of a typical .22 Long Rifle bullet.

.17 Hornady Mach 2
Left: .17 HM2, Right: .17 HMR
TypeRifle
Place of originUnited States
Production history
DesignerHornady
Designed2004
ManufacturerCCI/Hornady/Eley
Produced2004–present
Specifications
Parent case.22 Stinger
Case typeRimmed, bottleneck
Bullet diameter.172 in (4.4 mm)
Land diameter.168 in (4.3 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)
Rim thickness.043 in (1.1 mm)
Case length.714 in (18.1 mm)
Overall length1.00 in (25 mm)
Primer typeRimfire
Maximum pressure24,000 psi (170 MPa)
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 [1]

Performance

The weight of the bullet is a key part of achieving a very high velocity for a rimfire round. It weighs only 17 grains (1.10 g) vs 30-40 grains (1.94-2.59 g) of a typical .22 LR bullet.[2] 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 2,100 ft/s (640 m/s).[3] The velocity is nearly double that of a standard .22 LR, which results in a much flatter trajectory out to its 175-yard (160 m) effective range.[4]

Converting rifles
Left: .17HM2, right: .22 LR

Since the .17 HM2 is based on the .22 LR, converting most bolt action firearms chambered in .22 LR 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. Conversion kits 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.[4]

See also

References
  1. "17 Mach 2 17 gr V-MAX Varmint Express Rimfire". hornady.com. Archived from the original on August 8, 2018. Retrieved August 8, 2018.
  2. ".17 Mach 2 Ballistics". Archived from the original on August 6, 2018. Retrieved August 6, 2018.
  3. Hawks, Chuck. "Hornady's .17 Mach 2". chuckhawks.com. Archived from the original on July 23, 2018. Retrieved August 8, 2018.
  4. Simpson, Layne (January 4, 2011). "The Ultimate Flyweight Match: .17 HM2 Vs. .22 LR". shootingtimes.com. Archived from the original on August 5, 2018. Retrieved August 5, 2018.

Further reading
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