The gearbox ties everything together, and its dimensions are critical for the simulation. The presets define the basic gearbox types, but the real values can differ by as much as 1 mm between models.
The basics
Pick the gearbox version (V2, V3, V2.5, V6, V7) in the Gearbox → version field. That sets the cylinder length and the baseline geometry for your mechanism type – V2 (M4, MP5), V3 (AK, G36, SIG), V6 (P90) and so on.
Depending on the gearbox type you pick, only compatible cylinders are offered – e.g. for a V2 gearbox you won’t be able to select the long V2.5 cylinder.
Measuring the gearbox
The gearbox inner length is the distance from the spring seat to where the front of the cylinder seats, as in the photo. Measure it with a long caliper and enter it into Gearbox → inner length.
Gearbox → cylinder length is the maximum stroke the piston has available, i.e. the distance from the front cylinder seat to the point the front face of the piston body (without the head) is pulled to before the gear releases it. As a rule that’s the length of the bore the cylinder sits in, but it’s safer to check it this way.
If a cylinder is a touch shorter, it will make no difference – the piston-head O-ring (that does the compression) never reaches the end of the cylinder. So a 71 mm cylinder behaves exactly like a 72 mm one.
Note: when you build your own preset, it’s important to pick the right gearbox type – it decides which cylinders the simulator offers you. Get the type wrong and it’ll offer incompatible cylinders.
For the fast and furious
Short-stroke
Short-stroke means removing a few teeth from the sector gear so it pulls the piston back less – the stroke is shorter. It’s usually done for a snappier response or with extremely high rates of fire. Shorter stroke is compensated with a stronger spring.
Under Advanced there’s a short-stroke (removed teeth) field – enter how many teeth you removed from the sector gear and the simulator shortens the piston stroke in the calculation. That way you can see exactly how strong a spring you need for the power you want.