Look at the gun script. Particles are made by applying variables to particle textures.
datablock ParticleData(GunSmokeParticle)
{
dragCoefficient = 3;
gravityCoefficient = -0.5;
inheritedVelFactor = 0.2;
constantAcceleration = 0.0;
lifetimeMS = 525;
lifetimeVarianceMS = 55;
textureName = "base/data/particles/cloud";
spinSpeed = 10.0;
spinRandomMin = -500.0;
spinRandomMax = 500.0;
colors[0] = "0.5 0.5 0.5 0.9";
colors[1] = "0.5 0.5 0.5 0.0";
sizes[0] = 0.15;
sizes[1] = 0.15;
useInvAlpha = false;
};
datablock ParticleEmitterData(GunSmokeEmitter)
{
ejectionPeriodMS = 3;
periodVarianceMS = 0;
ejectionVelocity = 1.0;
velocityVariance = 1.0;
ejectionOffset = 0.0;
thetaMin = 0;
thetaMax = 90;
phiReferenceVel = 0;
phiVariance = 360;
overrideAdvance = false;
particles = "GunSmokeParticle";
};