Power factor (pistol)
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In competitive practical shooting, power factor refers to a ranking system for the momentum of pistol cartridges. The power factor is used in competitions sponsored by IPSC, USPSA, The Bianchi Cup, Steel Challenge, and IDPA.
IPSC/USPSA Power factor
IPSC and USPSA provide for two power factors, major and minor. The basis for power factor is the assumption that in a real-life encounter, a center hit from either will suffice to end the fight. Lesser-power cartridges will have less effect as the hits occur further from the center. The scoring would thus be: for a center, next scoring area and most-outside scoring area: Major; 5-4-2. Minor; 5-3-1. Poor hits (i.e. less-accurate marksmanship) are penalized, and the lesser cartridge is penalized more.
The power factor is calculated by multiplying bullet weight (in grains, 7,000 to the pound) by muzzle velocity (in feet per second), then dividing by 1000. As of 2014, a value of 165 or greater is considered major, while values below 165 are minor. Until a point in the late 1990s, the cut off point for "making major" was 175.
All firearms must have a minimum power factor of 125 for USPSA competition, and virtually anything of 9mm Luger or greater caliber will fit into minor. The minimum power factor is required since less-powerful cartridges have lower recoil and can be fired more quickly; setting a minimum value emphasizes the shooter's skill.
The desire to "make major" is a large part of the popularity of high velocity 9mm cartridges in this type of competition. .38 Super and other similar cartridges can be loaded to make major power factor. The felt recoil of a 9mm at Major is much the same as it would be for a .45. However, its higher operating pressure (.45: 17,000PSI, .38 Super: 34,000PSI)provides the Super a greater amount of higher-pressure gases to the muzzle brake. Open Division pistols are allowed a muzzle brake, and the re-directed gases act to dampen felt recoil and muzzle rise. Other USPSA equipment Divisions are not permitted muzzle brakes, thus the .38 Super or one of its derivatives (e.g., 9mm Major or 9x23) are not common outside of those two Divisions. In all divisions except Open and Revolver, the minimum bullet diameter to "make major" is .400" (.40 Smith and Wesson/10mm). In IPSC, Modified pistols were allowed muzzle brakes, but the division was retired after the World Shoot in 2011.
Major/Minor scoring occurs in USPSA in Open, Limited, Limited 10, Single Stack and Revolver Divisions. In production Division, only Minor is permitted. Use of major ammo will not give any scoring advantage. In IPSC competitions, Open, Standard, and Revolver Standard are Major/Minor, and Production is only Minor.
IDPA Power Factor
The IDPA also has a "power factor", and it is calculated the same way, however there is no scoring distinction between major and minor as in USPSA. A particular IDPA division has a minimum power factor, and the firearm must meet or exceed this minimum to be legal for competition. The minimum power factor is 125 for all divisions, except Custom Defensive Pistol (which is restricted to semiautomatics chambered for .45 ACP) and Enhanced Service Revolver division, which have power factors of 165.
In all instances, it is up to the competitor to ensure his/her ammunition meets the requirements for the competition or equipment Division.
Effective 1/17/11 the power factor for the stock service revolver division (SSR) was reduced to 105 since most factory produced .38 special ammunition available on the market did not meet the previous minimum power factor of 125.
NRA Action Pistol
In the Bianchi Cup, all matches requiring the use of centerfire ammunition must meet or exceed power floor of 120,000, or 120 Power Factor.
A minimum power factor of 120 was required to activate the stop plate in years past, which stops the time. The minimum power factor rule no longer applies.
Verifying Power Factor During Competition
For all major shooting competitions, claimed power factors are checked by firing the competitor's gun and ammunition through a chronograph. The most common practice is for a competitor to provide a certain number of rounds to the Range/Safety Officers at the beginning of the match day. During the course of the match, the Range/Safety Officers at the chronograph station will pull a bullet from the competitor's ammunition and weigh it. When the competitor arrives at the chronograph station, they provide their pistol and an empty magazine to the Range/Safety Officer who loads a number of rounds into the magazine and fires them through the chronograph to determine the ammunition's velocity. The power factor is verified against the competitor's claimed power factor. If a competitor claims major power factor and fails to achieve it, they are moved to minor and their targets are scored accordingly. If a competitor fails to make minor power factor, they generally can continue to shoot the match, but will do so for no score.
At local (often referred to as "club") matches, it is rare to verify the competitors' claimed power factor, except to ensure the minimum caliber is met (e.g., a USPSA Limited shooter using a 9mm bullet and claiming Major power factor).