BB Ballistics & Hop-Up

Airsoft Multiplayer simulates the trajectory of every single BB physically. Here's what's actually behind the values FPS, joules and hop-up.

FPS – Muzzle Velocity

FPS (feet per second) is the velocity of the BB right after it leaves the barrel. An MP5 in this game runs at around 375 fps, a sniper DMR around 750 fps. Higher FPS means a flatter trajectory and shorter time-to-target – but also more energy per hit.

Joules – Muzzle Energy

Joules describe the kinetic energy of the BB. It depends on velocity and BB weight: E = ½ · m · v². A 0.25 g BB at 350 fps reaches about 1.4 J. In game: more joules = more impactful hits – the sniper sits at ~6.6 J, way above any other weapon.

Hop-Up & the Magnus Effect

Hop-up puts a backspin on the BB as it leaves the barrel. The resulting Magnus effect creates lift and counteracts gravity – the BB flies much further and flatter than without spin. Too much hop-up and the BB lifts up and away, too little and it drops after 15 m. In game, hop-up is calibrated to a clean default (0.11); sniper and shotgun get less spin – producing a flatter, harder trajectory.

BB Weight

Heavier BBs (0.28 g, 0.32 g) are more wind-stable and carry their energy further, but are slower. Lighter BBs (0.20 g) start fast but lose energy rapidly and get pushed around by wind. For realistic CQB, the game defaults to 0.25 g.

Effective Range

Effective range is the distance at which a BB still arrives accurately and with enough energy. Full-auto guns like the Vector and MP5 are strongest at 20–35 m, the sniper stays precise well past 50 m. The shotgun spreads on purpose – its pellets cover a cone of ~10–15°.

See how these values play out across each gun: Weapon overview.