Measurement conversions and precision calculations
The kinetic energy calculated here can be used directly as the "Bullet kinetic energy" input in the TOP Gun Precision tab to estimate your rifle system's baseline precision.
| Calibre | Common weight(s) | Weight range |
|---|---|---|
| Pistol | ||
| .22 LR | 40 gr | 30–40 gr |
| 9mm Luger | 115 gr, 124 gr | 90–147+ gr |
| .40 S&W | 165 gr, 180 gr | 105–200 gr |
| .45 ACP | 230 gr | 68–300 gr |
| Rifle | ||
| .223 Rem / 5.56mm | 55 gr, 62 gr | 40–80+ gr |
| 6.5 Creedmoor | 140–150 gr | 95–150 gr |
| .308 Win | 150 gr, 165 gr, 180 gr | 100–240 gr |
| .30-06 Sprg | 150 gr, 165 gr, 180 gr | 110–220 gr |
| Calibre | Velocity (fps) | Velocity (m/s) |
|---|---|---|
| Pistol | ||
| .380 ACP | 900–1,800 fps | ~275–550 m/s |
| 9mm | 900–1,500 fps | ~275–457 m/s |
| .45 ACP | 750–1,300 fps | ~230–396 m/s |
| Rifle | ||
| .22 LR | 1,200–1,800 fps | ~366–550 m/s |
| .223 / 5.56 | 2,500–4,000 fps | ~762–1,219 m/s |
| 6.5 Creedmoor | 2,500–3,000 fps | ~762–914 m/s |
| .308 Win | 2,500–3,500 fps | ~762–1,067 m/s |
Precision (MOA) is calculated using the Applied Ballistics "TOP Gun" formula: Bullet Energy (ft·lbf) ÷ 200 ÷ Rifle Weight (lbs). This estimates the average 5-shot extreme spread at 100 yards for a given rifle system. [2]
Mean radius represents the average distance of each shot from the centre of the group. Unlike extreme spread (which only measures the two worst shots), mean radius accounts for every shot in the group, making it more statistically meaningful—especially for smaller sample sizes. [2] The conversion uses a coefficient of 0.428 derived from simulation of approximately 1 million 5-shot groups. [2]
See this Reddit post for further details on the mean radius derivation →
| Cartridge | Muzzle energy (Joules) | Muzzle energy (ft·lbf) |
|---|---|---|
| 9mm Parabellum | ~480 – 700 J | ~350 – 500 ft·lbf |
| 5.56 NATO (rifle) | ~1,700 – 1,800 J | ~1,250 – 1,330 ft·lbf |
| .308 Winchester (rifle) | ~3,300 J | ~2,400 ft·lbf |
| .30-06 Springfield (rifle) | ~3,000 – 4,000 J | ~2,000 – 3,000 ft·lbf |
| .50 BMG (anti-materiel) | ~14,000 – 20,000 J | ~10,000 – 15,000 ft·lbf |
| Application | Weight range (lbs) | Notes |
|---|---|---|
| Lightweight/Backcountry hunting | 5 – 8 lbs | Prioritises portability over long distances |
| General hunting | 6 – 12 lbs | Balance between portability and stability |
| Tactical/Defence (M4, AR-15) | 6.5 – 10 lbs | Robustness, reliability, manoeuvrability |
| Varmint shooting | 7 – 10 lbs | Compromise for long-range precision |
| Target/Competition (PRS, Benchrest) | 10 – 25+ lbs | Maximises stability, minimises recoil |
Calculate the minimum number of shots per group to statistically determine a difference between two loads with >95% confidence.
This calculator is based on the work of Chris Hague at Hague & Sons Precision Gunsmithing. It determines the minimum sample size needed to statistically differentiate between two loads at a 95% confidence level.
The formula used is:
Where R1 and R2 are the mean radii of Load #1 and Load #2 respectively, and the result is rounded up (ceiling function). A minimum of 10 shots is always required regardless of the calculation.
Interpretation: If the loads truly differ by the amounts you entered, shooting this many rounds per group gives you at least 95% confidence that any observed difference is real, not random chance.
Minimum number of shots in EACH group to have >95% confidence the loads are different
Convert your observed extreme spread (ES) to an estimated mean radius (MR) distribution based on Monte Carlo simulation of 1,000,000 shot groups.
Compare your rifle's precision against standard BPC classes. Based on your observed extreme spread, we estimate the underlying sigma (σ) and compare it to each class threshold.
| BPC Class | Sigma (σ) | Median 5-shot Group Spread | Typical Examples | Your Results |
|---|
Ballistic Precision Classification (BPC) is a standardised system for describing rifle precision. It uses sigma (σ), the statistical parameter of the Rayleigh distribution, to characterise accuracy. Lower BPC classes indicate better precision.
Your Results interpretation:
Extreme Spread (ES) measures the maximum distance between any two shots in a group. Mean Radius (MR) measures the average distance of each shot from the group centre.
Because ES only considers the two most extreme shots, it's highly variable—especially with small sample sizes. Mean radius accounts for every shot, making it more statistically stable and meaningful for comparing precision.
This calculator uses Monte Carlo simulation (1,000,000 groups per sample size) to estimate the distribution of mean radius values you might observe for a given extreme spread. The percentiles represent:
Mean radius values (MOA) for each extreme spread and shot count combination.