Chronograph

Every UK airsoft site has FPS limits enforced via chrono testing on arrival — typically 350 FPS for AEGs in full-auto, 450 FPS for DMRs in semi, 500 FPS for snipers in bolt-action. If your rifle tests above the limit on site chrono, you're either spending the day with the wrong rifle or being sent home. A home chronograph lets you catch the problem before you leave the house, when there's still time to fix the rifle, swap in lighter BBs, or pick a different primary.

Two chrono designs cover the airsoft market. Sky-screen chronographs are the older standard — two parallel photodetectors mounted in a frame, you shoot through the gap, the chrono measures the time-of-flight between the two screens and calculates FPS. Accurate but bulky and light-sensitive (don't work well outdoors in bright sun or indoors under fluorescents). Suppressor-mount and barrel-mount chronographs are the modern compact alternative — clip to the muzzle, measure BB velocity at the moment of exit, lighter and more portable, less sensitive to ambient light.

What to look for. Joule readout as well as FPS is essential — UK sites cap by joule, not raw FPS, because heavier BBs at lower FPS can exceed joule limits while looking legal on an FPS-only readout. BB weight selector so the chrono knows what BB you're shooting and can calculate joules accurately. Multi-shot averaging to filter outliers across 5-10 shots. Bluetooth/app integration for logging is nice-to-have but not essential. Pair with the right BB weights for accurate readings — test with the BB weight you'll actually run on the field, not just whatever's in the bag.