Chronograph Guide — Measuring FPS Correctly
A chronograph measures your BB's muzzle velocity. It's essential for passing field checks, monitoring your gun's health and verifying upgrades — but sloppy technique produces misleading numbers.
Proper measuring procedure
- Use a consistent BB weight — 0.20g is the common reference. If your field chronos with a different weight, follow their rule.
- Muzzle close to the sensor, in line — keep the distance your device recommends (usually 5–30 cm) and shoot straight through; angled shots skew readings.
- Fire at least 5–10 shots — judge the average and the spread, not a single shot. A large spread (±) hints at hop rubber or cylinder seal problems.
- Record your hop-up setting — readings can shift with hop pressure (especially on gas guns), so keep it consistent.
Converting readings to energy
Energy is E = ½mv². 330 fps on 0.20g is about 1.01 J. Skip the
hand math — enter your weight and measured FPS into the
ballistics calculator and you'll get the energy plus the
equivalent FPS for every other weight, which is handy when you chrono on
0.20g but play with 0.28g.
Watch out for joule creep
Gas and HPA guns can deliver more energy with heavier BBs than the 0.20g reading suggests: a heavier BB stays in the barrel longer and absorbs more of the expanding gas. A gas sniper chronoing 1 J on 0.20g may exceed 1.3 J on 0.40g. Be a fair player — chrono with the weight you actually use; many fields now require it. (Spring/AEG guns barely exhibit this.)
Troubleshooting odd readings
- Spread over ±15 fps: worn hop rubber, poor cylinder seal, inconsistent BBs
- Overall drop vs last session: tired spring, worn piston head/o-ring, low gas
- No reading / wild values: fluorescent light interference, wrong muzzle distance
Wondering how your measured FPS translates into range? Read how to read ballistics results next.