Air rifle and air pistol power: joules, ft-lb and accuracy

• Muzzle energy is the energy a pellet carries out of the barrel: half its mass times its speed squared. In metric units it comes out in joules (J); many makers also give it in foot-pounds (ft-lb).
• Speed alone does not tell you the power. A lighter pellet leaves the same rifle faster, and can still carry less energy.
• A 10 m match rifle is low-powered by design: ISSF rules cap it at 7.5 joules for matches, and the pellet only has to cross 10 metres and cut a clean hole.
• More power does not make a rifle more accurate. Tight groups come from a rifle that repeats itself, a pellet that fits the barrel and a hold that stays the same.
• Whether the law where you live limits a rifle’s power, or ties a licence to it, is a separate question from any match rule: see the law where you live.

Kinetic energy, the energy of motion, is one-half the mass times the square of the speed: E = ½mv² (OpenStax University Physics, 7.2). Put the mass in kilograms and the speed in metres per second, and the answer comes out in joules.

The square is what matters. Twice the mass at the same speed carries twice the energy; twice the speed carries four times as much.

That is why a speed on its own says little. A lighter pellet leaves the same rifle faster: JSB makes lighter match pellets for air pistols for exactly that, a higher muzzle velocity. Faster is not the same as more powerful, though. Air Arms, a British maker, puts it plainly: a very light pellet fired at high velocity can carry far less energy than a heavier one moving more slowly, so velocity alone is not a reliable measure of power.

Two makers’ figures make a 10 m example. H&N gives its Finale Match Light pellet a weight of 7.87 grains. Feinwerkbau gives its 800 X match rifle a muzzle velocity of 170 to 175 m/s; take the low end.

1. The mass in kilograms: 7.87 grains × 0.0648 = 0.510 g, which is 0.000510 kg.
2. The speed squared: 170 × 170 = 28,900.
3. The energy: ½ × 0.000510 × 28,900 = 7.37 joules.
4. In foot-pounds: 7.37 ÷ 1.356 = 5.4 ft-lb.

So about 7.4 J, just under the 7.5 J that ISSF rules allow a match rifle (see below). Call it an estimate, because the speed depends on the pellet and Feinwerkbau names none. The same 170 m/s with H&N’s heavier Finale Match Heavy, 8.18 grains (0.530 g), would give 7.66 J, over that ceiling: a rifle within the rule drives a heavier pellet more slowly. Your own gun’s figure, with your own pellet, takes a chronograph, a meter that times each pellet as it passes.

You can check the formula against a maker that gives all three numbers. Anschütz says its 9015 High Power action, sold for field target, delivers 15 joules and drives 0.68 g pellets at up to 210 m/s: ½ × 0.00068 × 210 × 210 = 14.99, the maker’s 15 J. A pellet a third heavier, flying about a quarter faster, carries about twice the energy of the match example. That is the square at work.

Every conversion is one multiplication. The factors below come from NIST’s Guide to the SI, rounded; the reverse ones are their reciprocals. Ft-lb in an air rifle specification means the foot-pound-force, which NIST writes ft·lbf.

In imperial units the match example reads 170 × 3.281 = 558 fps, and 7.37 × 0.7376 = 5.4 ft-lb. If your chronograph reads in fps and your tin gives grains, you can stay in imperial units: energy in ft-lb = grains × fps × fps ÷ 450,437, a constant that follows from the same NIST factors. For the match pellet, 7.87 × 558 × 558 ÷ 450,437 = 5.4 ft-lb again.

The rifle you shoot in an ISSF 10 m match has a ceiling on its power:

Rifle

Any type of compressed air or gas rifle that meets the rules’ measurements table and the air rifle restrictions.ISSF Rifle Rules 7.4.4

Energy

A 10 m air rifle must not exceed 7.5 joules and must bear the mark of an F in a pentagon.ISSF Rifle Rules 7.4.4 c, ISSF Rule Book, Edition 2025 (Second Print 07/2026), effective 1 July 2026

That is a sporting rule for ISSF matches, not the law where you live. What the law says about a rifle’s power is a separate question, answered for your country in the law where you live.

The pistol rules set no such ceiling: for 10 m air pistol, any 4.5 mm compressed-air, CO2 or pneumatic pistol that conforms to the specification table and configuration drawing may be used (ISSF Pistol Rules 8.4.3.5). A match pistol is low-powered all the same, built for the same ten metres and the same clean hole, and lighter pellets are made for it: JSB offers its 0.475 and 0.500 g match pellets for the pistol, for a higher muzzle velocity. The law, where it limits an airgun’s power, sometimes draws the pistol’s line lower than the rifle’s — Air Arms, writing about air pistols in Britain, notes that what the lower power envelope limits is longer-range shooting, not the 10 m card. Which line applies to you is in the law where you live; the card is on the ISSF 10 m air pistol target page.

The ceiling costs a match shooter nothing, because the job is small. The pellet has to cross 10 metres and cut a clean, round hole in paper. JSB makes its match pellets primarily for target shooting at 10 m, with a flat head for round, sharp holes, and H&N gives its Finale Match a maximum distance of 10 m. Air Arms notes that target shooting needs only minimal energy transfer to punch through paper precisely.

What a match rifle is built for instead is sameness. Feinwerkbau describes its 800 series by fast shot development, recoilless firing, constant energy and precision, not by power.

Low-powered does not mean harmless. A 10 m match rifle can still injure: treat it as loaded, never point it at anyone, and shoot only where the pellet stops in a trap or backstop rated for the rifle. A more powerful rifle needs a trap rated for its power, so ask before you bring one to a club range.

Umarex, an air gun maker, defines accuracy not as how fast or how powerful a rifle is, but as how consistently it places pellets where the shooter intends. If the barrel, the pellet and the rifle do not work together, it adds, more power does not save the group.

At 10 m, extra speed buys almost nothing. An estimate, leaving out air resistance: at 170 m/s a pellet takes 10 ÷ 170 = 0.059 seconds to reach the target, and in that time it falls ½ × 9.81 × 0.059 × 0.059 = about 17 mm (gravity and the formula are from OpenStax University Physics, 3.5). At 210 m/s it would fall about 11 mm. Air resistance slows the pellet, so the real drop is a little larger. Either way your sights are set for it, and it costs you nothing as long as it is the same every shot.

Further out, speed does help. Air Arms credits the faster .177 calibre with a flatter trajectory, ideal for long-range shooting where precision is paramount, though the same page says its lighter pellets deliver less energy on impact. That is speed, not power, and it pays at long range, not on a 10 m range.

A rifle that gives the same energy every shot helps keep the group tight. Air Arms, writing about air pistols, says shot-to-shot consistency in energy output matters more than peak power in many recreational uses. How a regulator keeps a PCP’s power the same is in the kinds of air rifle; finding the pellet your barrel likes is in choosing pellets.

• Compare energy, not speed. A velocity means little without the weight of the pellet it was measured with.
• A maker’s figure belongs to its own test. Air Arms warns that a published figure should not automatically be assumed to apply identically to every individual gun.
• For your own rifle, use a chronograph and your own pellet. Look at how much the shots vary, not only at the average.
• For 10 m, do not shop by power. Buy for fit and for a rifle that repeats itself: Choosing your first air rifle goes through what to check.
• Before you buy a rifle, or change its power, read the law where you live: power can decide what licence, if any, the rifle needs.

How do I convert ft-lb to joules?

Multiply by 1.356, NIST’s factor rounded. To go from joules to ft-lb, multiply by its reciprocal, 0.7376.

Is fps or joules the better measure of an air rifle’s power?

Joules, or ft-lb. Energy takes in both the pellet’s weight and its speed, while a speed alone depends on how light a pellet it was measured with.

Will a more powerful air rifle shoot tighter groups?

Not by itself. At 10 m the extra speed changes the drop by a few millimetres that your sights already take out. Groups come from a rifle that repeats itself, a pellet that fits and a steady hold.