Power factor (shooting sports)

Limitations

Measuring the power factor is a quick and easy way to measure recoil, but has some drawbacks. While the power factor measures the momentum of the fired bullet, it doesn't take into consideration the firearm weight or the contribution from the ejected propellant gases which together makes up for the total recoil impulse from the firearm. The contribution from propellant gases depends on the amount of gunpowder and the effectiveness of any muzzle brake or suppressor. The power factor also doesn't take into consideration any angular momentum or torque, i.e. any lever arm caused by an offset between the bore axis of the firearm to the contact point on the shooter. Also, recoil can alternatively be measured by recoil velocity or recoil energy instead of by recoil impulse.

An alternative formula for simplified recoil measurement which also takes into account firearm weight, gun powder weight and the velocity of the gun powder gases has been suggested:

${\displaystyle \text{recoil impulse}=\frac{\text{(bullet weight × bullet velocity) + (powder weight × powder velocity) }}{\text{firearm weight}}}$

Gunpowder velocity depends on the amount and type of powder (burn rate) etc. Assuming that the average velocity of the powder gases is half the bullet muzzle velocity, the formula can be simplified to the following:

${\displaystyle \text{recoil impulse}=\frac{\text{(bullet weight + half the powder weight) × bullet velocity}}{\text{firearm weight}}}$

Various shooting organizations

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 noticeable difference in terminal performance correlating to the recoil difference between typical minor and major handgun calibers. 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 (≈ 2.47 newton seconds), and therefore almost anything of 9×19mm 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.

Handgun

The desire to get the benefit of major scoring has led to some competitors adopting 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 became popular in the early 1980s, and has continued to be popular in the open division after its introduction in the 1993 season.

• In the open division, IPSC has a lower power factor requirement of 160 kgr·ft/s for major, while the other IPSC handgun divisions require a power factor of 170 kgr·ft/s for major. Open and revolver are also the only divisions that allows major scoring with a 9 mm bullet diameter (the other handgun divisions require a 10 mm bullet diameter). Together with muzzle brakes only being allowed in the Open division, this has made the .38 Super and 9×19mm cartridge loaded to major become a popular option in the open division in recent years. Higher operating pressures of the cartridges like the 9×19mm major and .38 Super are preferred over, for instance, the .45 ACP, since it provides more gases for the compensator, dampening the felt recoil and muzzle rise more. Other handgun divisions are not permitted muzzle brakes, making 9 mm major and .38 Super uncommon outside open and revolver.
• In the standard division, the bullet caliber must be at least 10 mm in order to achieve major scoring, leading to less magazine capacity, and the competitor therefore has to make a choice between minor and major considering the difference in recoil, magazine capacity and points on target. It is a common belief that major scoring will give better results, but the main downside is more expensive and less available ammunition.
• In the production division extra points are not awarded for Major power factor, and thus the competition is dominated by 9×19mm caliber loaded to minor power factor. This, amongst other reasons, is why the production division currently is the most popular division.
• In the classic division a choice can be made between up to a 10-shot capacity 1911 with minor scoring (e.g. 9×19mm) or up to an eight-shot capacity 1911 with major scoring (e.g. .40 S&W or .45 ACP).
• In the revolver division major scoring can be achieved with a 9 mm bullet diameter, but with a power factor of 170. A popular cartridge in revolver is the .45 ACP since it is easier to use with speed loaders. From 2017, revolvers with a capacity of seven rounds or more are scored with minor power factor.

Rifle

In both the open and standard rifle divisions, minor power factor is dominating due to less recoil, and 5.56×45mm/ .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, and 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 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, 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. Until a point in the late 1990s, the cut off point for "making major" was 175 kgr·ft/s.

Steel Challenge

A minimum power factor of 120 kgr·ft/s (≈ 2.37 N⋅s) 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. Instead 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/ammunition combination must meet or exceed this minimum to be legal for competition. The minimum power factor was previously set as 125 kgr·ft/s for all divisions, except custom defensive pistol (which is restricted to semiautomatics chambered for .45 ACP), which had a power factor of 165 kgr·ft/s.

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

Effective on 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.

To correlate with commonly available ammunition for firearms within a given division, revised power factors were established, effective 1 January 2017.

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 ( ≈ 2.37 N⋅s).