Power factor (shooting sports)

A high-speed photography of a .38 Special bullet fired out of a Smith & Wesson Model 686 revolver.

Power Factor (PF) in practical shooting competitions refers to a ranking system used to reward cartridges with more recoil. Power factor is a measure of the momentum of the bullet (scaled product of the bullet's mass and velocity).

Power factor is used in competitions sanctioned by the International Practical Shooting Confederation (IPSC), United States Practical Shooting Association (USPSA), Bianchi Cup, Steel Challenge and International Defensive Pistol Association (IDPA).

Calculation

The power factor is based on the bullets momentum as it's moving through the air by measuring the bullet speed using a chronograph and measuring a similar bullet mass on a weighing scale, thereafter calculating the power factor by the formula:

The power factor can be represented using different units:

Since by definition 1 gram = 15.4323584 grains and 1 m/s = 3.2808399 ft/s, their product is 50.6310987 and the two units can be converted back and forth using the following relationship

and

Examples of different loads

Note that the table below are examples, and for the same caliber different bullet weights can be used. Bullet velocity depends amongst other on bullet weight, powder types used and barrel length for the particular firearm.

Cartridge Bullet mass
(grains)
Muzzle velocity
(ft/s)
Power Factor
(kgr·ft/s)
Bullet mass
(gram)
Muzzle velocity
(m/s)
Power Factor
(newton seconds)
9x19 mm 116 gr 1,150 ft/s 133 kgr·ft/s 7.5 g 350 m/s 2.6 Ns
.40 S&W 155 gr 1,200 ft/s 186 kgr·ft/s 10 g 366 m/s 3.7 Ns
10mm 220 gr 1,250 ft/s 275 kgr·ft/s 14.3 g 381 m/s 5.5 Ns
5.56 NATO 62 gr 3,100 ft/s 192 kgr·ft/s 4 g 945 m/s 3.8 Ns
7.62 NATO 175 gr 2,590 ft/s 453 kgr·ft/s 11 g 790 m/s 8.7 Ns
12 gauge 118 oz
(492 gr)
1,200 ft/s 591 kgr·ft/s 32 g 366 m/s 11.7 Ns
12.7×99mm NATO 750 gr 2,820 ft/s 2,115 kgr·ft/s 50 g 860 m/s 43 Ns

Verifying 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., an IPSC Standard shooter using a 9 mm bullet and claiming Major power factor).

Various shooting organisations

International Practical Shooting Confederation

IPSC provides the two power factors Minor and Major which have different scoring points on paper targets. The IPSC Target has the three scoring zones A, C, and D, with the points 5-3-1 for Minor and 5-4-2 for Major. Good hits are scored equally regardless of power factor, while lesser hits are penalized less with Major power factor. The concept historically originates from the idea that a lesser hit with a harder hitting caliber will be more likely to end a firefight in a real life situation. However, modern ballistic studies have shown no noticable difference in terminal performance correlating to the recoil difference between typical minor and major handgun calibers.[1] On the other hand, the power factor requirement has been kept to award the greater challenge of marksmanship required by competitors to shoot firearms with more recoil well.

In IPSC competitions all handguns must have a power factor of at least 125 kgr·ft/s (2.5 newton seconds), and therefore almost anything of 9x19 mm or greater caliber will meet the minimum required power factor. The minimum power factor rule is designed to mitigate the speed and accuracy advantages of smaller calibers. Less-powerful cartridges have less recoil, and therefore can be fired more quickly with the same accuracy. Setting a minimum power factor value requires recoil management skills by all competitors.

Division Minor
scoring
Major
scoring
Handgun
Production
125 kgr·ft/s (2.5 Ns)
Only minor scoring
Handgun
Standard, Classic, Revolver
125 kgr·ft/s (2.5 Ns) 170 kgr·ft/s (3.4 Ns)
Handgun
Open
125 kgr·ft/s (2.5 Ns) 160 kgr·ft/s (3.2 Ns)
Rifle
All divisions
150 kgr·ft/s (3 Ns) 320 kgr·ft/s (6.3 Ns)
Shotgun
All divisions
480 kgr·ft/s (9.5 Ns)
Only major scoring

Handgun

The desire to get the benefit of major scoring has led to the development of high speed 9 mm cartridges loaded to major, such as .38 Super. The felt recoil of a normal handgun in .38 Super is similar to the .45 ACP, but the higher pressure in the .38 Super provides more gas pressure for muzzle brakes. The .38 Super caliber got popular in the early 80's, and has continued to be popular in the Open division after its introduction in the 1993 season.

Rifle

In both the Open- and Standard rifle divisions, minor power factor is dominating due to less recoil, and 5.56x45mm/ .223 Rem is a common caliber. Ammunition loaded to major power factor such as 7.62×51 mm/ .308 Win has a bigger recoil impulse, and is regarded as having an advantage on stages with targets at long range.

Shotgun

In shotgun only a Major power factor of 480 kgr·ft/s is used throughout all divisions. 12 gauge is the most common caliber, an most handle the recoil well. The extra power of a 12 gauge gives the competitors better margins of error when it comes to hit steel targets. Although 12 gauge is most prevalent for both male and female shooters, it is also possible to use other calibers, such as the smaller 16 or 20 gauge. The smallest 20 gauge has the advantage that it is easier to carry and for the shooter to keep balance while shooting, thus making it easier to shoot more accurately. However the smaller caliber requires however more precision, especially on small steel targets.

United States Practical Shooting Association

USPSA also provide Minor and Major scoring based on power factor. Metric targets are divided into the scoring areas A, B, C and D with Minor and Major points 5-3-3-1 and 5-4-4-2 respectively, while IPSC Targets are divided into the scoring areas A, C and D with Minor and Major points 5-3-1 and 5-4-2 respectively.

In USPSA as of 2014, a value of 165 kgr·ft/s or greater is considered Major for all divisions (except Production and Carry Optics where there only is minor scoring), while values below 165 kgr·ft/s are Minor.[2] Until a point in the late 1990s, the cut off point for "making Major" was 175 kgr·ft/s.

Division Minor
scoring
Major
scoring
Handgun
Production, Carry Optics,
125 kgr·ft/s (2.5 Ns)
Only minor scoring
Handgun
Open, Limited, Limited-10, Revolver
125 kgr·ft/s (2.5 Ns) 164 kgr·ft/s (3.3 Ns)

Steel Challenge

A minimum power factor of 120 kgr·ft/s (2.4 Ns) was previously required to activate the stop plate which stops the competitors time, but since around 2011 the stop plates are no longer connected to timers. Insted regular shot timers that register the last shot fired are used. Therefore the minimum power factor rule no longer applies, and competitors are encouraged to use low power factor ammo in order to preserve the steel targets.

International Defensive Pistol Association

The IDPA also has different power factors, and they are calculated the same way, however there is no scoring distinction 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 kgr·ft/s for all divisions, except Custom Defensive Pistol (which is restricted to semiautomatics chambered for .45 ACP), which has a power factor of 165 kgr·ft/s.[3]

In all instances, it is up to the competitor to ensure his/her ammunition meets the requirements for the competition or equipment Division.

Effective 17 January 2011 the power factor for the stock service revolver division (SSR) was reduced to 105 kgr·ft/s since most factory produced .38 special ammunition available on the market did not meet the previous minimum power factor of 125 kgr·ft/s.[4]

NRA Action Pistol

In the Bianchi Cup, all matches requiring the use of centerfire ammunition must meet or exceed a power factor of 120 kgr·ft/s.

See also

References

  1. FBI Training Division Justifies 9mm Caliber Selection - The Firearm Blog
  2. "USPSA Rule Book, Appendix D1" (PDF). USPSA. Retrieved 24 June 2014.
  3. "IDPA Rule Book, Appendix One" (PDF). IDPA. Retrieved 7 April 2014.
  4. "IDPA web notice". IDPA. Retrieved 31 January 2012.
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