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About

Airsoft fields enforce strict muzzle energy limits to ensure player safety. While velocity (FPS) is the common measurement, energy (Joules) is the true determinant of impact force. A heavy BB travels slower than a light one but may carry the same or more energy, potentially violating site rules. This discrepancy makes Joule calculation mandatory for chronograph testing.

This tool converts mass and velocity inputs into kinetic energy. It compares the result against standard safety limits used in the UK, EU, and US. Identifying whether a replica falls within "CQB" (Close Quarters Battle) or "DMR" (Designated Marksman Rifle) classifications prevents disqualification on game day.

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Formulas

The kinetic energy (Ek) is calculated using the standard physics formula, where mass (m) is in kilograms and velocity (v) is in meters per second.

Ek = 0.5 m v2

Since inputs are often in grams (g) and feet per second (FPS), conversions are applied:

mkg = mg1000
vm/s = vfps × 0.3048

Reference Data

ClassificationLimit (Joules)Approx. FPS (0.20g)Usage Context
CQB / Indoor 1.14 J350 FPSStrict limit for close engagement.
Outdoor Automatic 1.49 J400 FPSStandard assault rifle limit (US/EU).
DMR (Semi-Locked) 1.88 J450 FPSMid-range support; minimum engagement distance.
Sniper (Bolt Action) 2.32 J500 FPSLong-range; strict engagement distance applies.

Frequently Asked Questions

Gas expansion physics (Joule Creep) means a heavier BB stays in the barrel longer, absorbing more energy from the expanding gas than a lighter BB would. Always chrono with the weight you intend to use.
No. 1.14J (approx 350 FPS w/ 0.20g) is standard for UK legal limits and many indoor sites. However, US fields often allow up to 1.5J (400 FPS) for outdoor play. Always check specific site rules.
Yes. A longer barrel allows more time for gas or air pressure to accelerate the BB, potentially increasing velocity and energy up to the point where the cylinder volume is exhausted.