Nobody wants to leave usable performance on the table. A rifle comes in reading a shade under the top of the class, and the question follows almost every time: can you get a bit more out of it? It is a fair question and it deserves a straight answer rather than an opinion. So we ran the numbers and drew the graphs.
Some of what follows can be calculated exactly. The rest depends on your pellet, your rifle and the day. We have labelled which is which throughout, so you always know what kind of number you are looking at.
One thing is worth knowing before any of it makes sense. Speed and energy do not rise together. Energy goes up with the square of velocity, so velocity goes up with the square root of energy. To double a pellet's speed you need four times the energy. Which means the closer you get to the top, the less speed each extra foot-pound buys you.
1. What changes at the muzzleExact calculation
This part needs no assumptions at all. Going from 11.4 to 11.9 ft/lb is a 4.39% increase in energy but only a 2.17% increase in muzzle speed. For any fixed pellet weight, that percentage is the same. Only the fps gain changes, becoming smaller as pellet weight increases.
| Pellet | At 11.4 ft/lb | At 11.9 ft/lb | Gain | Speed change |
|---|---|---|---|---|
| 8.44 gr · .177 | 780 | 797 | +16.9 | +2.17% |
| 10.34 gr · .177 | 705 | 720 | +15.3 | +2.17% |
| 14.35 gr · .22 | 598 | 611 | +13.0 | +2.17% |
| 15.89 gr · .22 | 568 | 581 | +12.3 | +2.17% |
The whole difference between the two is half a foot-pound.
Velocity follows the square root of energy, so the curve flattens as it climbs. Every extra foot-pound buys less speed than the one before it. The shaded band is the 11.4 to 11.9 ft/lb comparison.
2. Every foot-pound buys less than the one before itExact calculation
The first foot-pound takes an 8.44 grain pellet from a standing start to 231 fps. The twelfth adds 34 fps. Same 1 ft/lb increase in energy, but only about one-seventh of the velocity gain.
8.44 gr .177. The other three pellets follow exactly the same shape at their own speeds.
A quarter of the energy gets you half the speed.
For the same pellet mass, and it follows directly from velocity tracking the square root of energy. For any fixed pellet mass, the same relationship applies regardless of calibre.
3. What it looks like down rangeWorked example
Here the honest answer changes shape. There is no universal millimeter figure for what half a foot-pound is worth at fifty yards, because once the pellet leaves the muzzle the answer depends on drag and sight geometry as well as speed. A single downrange figure only has meaning when the assumptions behind it are stated.
So here is one worked example with its inputs listed, so the assumptions behind the figure are visible rather than hidden.
Inputs used for this example
- Pellet — JSB Exact Diabolo 8.44 gr, .177
- Drag model — GA, the model built for diabolo pellets
- Ballistic coefficient — 0.019, field tested
- Muzzle velocity — 779.8 fps and 796.8 fps
- Sight height — 40 mm above bore
- Zero — 30 yards (27 m), both rifles
- Atmosphere — 15 °C, 1013.25 hPa, dry air — standard sea-level, air density 1.225 kg/m³
Both rifles zeroed at 30 yards. Two separate lines, drawn to scale — they only begin to part company past forty yards.
On these stated inputs, the difference at fifty yards is 4.4 mm — about a sixth of an inch, and close to the width of the pellet itself. Change the pellet, the ballistic coefficient, the sight height, the zero or the atmospheric conditions and the figure will also change.
4. The full calculated tableExact calculation
Every step from nothing to the top of the class, for all four pellets. Speeds and gains are calculated first, then rounded for display. Read down the gain columns and watch them collapse.
| Step | Energy | 8.44 gr · .177 | 10.34 gr · .177 | 14.35 gr · .22 | 15.89 gr · .22 | ||||
|---|---|---|---|---|---|---|---|---|---|
| Speed | Gained | Speed | Gained | Speed | Gained | Speed | Gained | ||
| 0 → 1 | 1 ft/lb | 231 | +231 | 209 | +209 | 177 | +177 | 168 | +168 |
| 1 → 2 | 2 ft/lb | 327 | +96 | 295 | +86 | 251 | +73 | 238 | +70 |
| 2 → 3 | 3 ft/lb | 400 | +73 | 361 | +66 | 307 | +56 | 292 | +54 |
| 3 → 4 | 4 ft/lb | 462 | +62 | 417 | +56 | 354 | +47 | 337 | +45 |
| 4 → 5 | 5 ft/lb | 516 | +55 | 467 | +49 | 396 | +42 | 376 | +40 |
| 5 → 6 | 6 ft/lb | 566 | +49 | 511 | +45 | 434 | +38 | 412 | +36 |
| 6 → 7 | 7 ft/lb | 611 | +45 | 552 | +41 | 469 | +35 | 445 | +33 |
| 7 → 8 | 8 ft/lb | 653 | +42 | 590 | +38 | 501 | +32 | 476 | +31 |
| 8 → 9 | 9 ft/lb | 693 | +40 | 626 | +36 | 531 | +30 | 505 | +29 |
| 9 → 10 | 10 ft/lb | 730 | +37 | 660 | +34 | 560 | +29 | 532 | +27 |
| 10 → 11 | 11 ft/lb | 766 | +36 | 692 | +32 | 587 | +27 | 558 | +26 |
| 11 → 12 | 12 ft/lb | 800 | +34 | 723 | +31 | 614 | +26 | 583 | +25 |
First row highlighted blue, final row highlighted red. For the 8.44 gr pellet, the first 1 ft/lb step produces 6.8 times the muzzle-velocity gain of the final 1 ft/lb step. The same ratio applies to every other pellet mass, because the mass term cancels when the two steps are compared.
5. So what is worth chasing?
- At the muzzle, exactly — 11.4 to 11.9 ft/lb is +0.50 ft/lb, +4.39% energy and +2.17% speed. In fps that is +16.9 (8.44 gr), +15.3 (10.34 gr), +13.0 (14.35 gr), +12.3 (15.89 gr).
- Downrange — on the inputs we stated, about 4.4 mm at fifty yards. Different inputs give a different figure, which is why the assumptions are listed rather than left out.
- Where the real gains are — not at the top. The first foot-pound produces nearly seven times the muzzle-velocity gain of the twelfth. By the time you are arguing about the last half, the curve has long since flattened.
- The practical priority — stable, repeatable, compliant performance beats chasing the highest single reading on a chronograph.
Before you chase the last half foot-pound
The numbers above are the answer to that question, and they are not our opinion — they are arithmetic. Two things worth doing before you spend money on half a foot-pound.
- Look at section 4 again. The first foot-pound produces nearly seven times the muzzle-velocity gain of the twelfth. By the time a rifle is up near the top of the class, the large velocity gains are well behind it.
- Look at section 1. For the same pellet, increasing muzzle energy from 11.4 to 11.9 ft-lb increases muzzle velocity by 2.17%, regardless of pellet weight. The four examples in the table show what that 2.17% equates to in fps, with heavier pellets gaining fewer fps.
When it is worth getting in touch
If your rifle has started behaving differently; the power has shifted, the consistency has dropped, or it is losing air; it is worth having it checked before making any adjustments. Poor grouping can come from the rifle itself, but it can just as easily be caused by pellets, optics, mounts, a moderator or setup. The first step is identifying the cause accurately. If it does turn out to be the rifle itself, and it’s a Daystate, Brocock, Air Arms or Weihrauch, get in touch if you need help with servicing, tuning or diagnosing the issue.
Absolute Airguns · Unit 12, Clarendon Court, Winwick Quay, Warrington WA2 8QP
Tel / WhatsApp 07386 906400 · By appointment, 8am–4pm Mon–Fri
Method. Muzzle energy from the standard airgun formula: pellet weight in grains, times velocity in fps squared, divided by 450,240. Everything badged exact calculation comes straight from that formula and is subject only to display rounding. The one section badged worked example comes from numerical integration of a point-mass trajectory at the ballistic coefficient, sight height, zero and atmosphere stated in section 3. Those are calculated figures for the inputs given, not measurements of any particular rifle, and they are offered so you can reproduce or challenge them rather than as universal facts. A different ballistics program, drag table or integration method may return a slightly different figure from the same inputs.