Quick answer: Construct 3 Bullet behavior projectiles unexpectedly speeding up or reversing? Acceleration applies along the bullet’s direction each second; Speed is current. Use Acceleration only when you want compounding.

A grenade has Acceleration = -200 expecting it to decelerate; on negative speeds it starts going backwards because acceleration continues to apply.

Acceleration Compounds

Acceleration changes speed each tick. Negative acceleration eventually flips speed to negative; the bullet reverses direction. Stops only when you cap or zero acceleration.

Use Set Speed Instead

Every tick:
  Bullet: Set Speed to max(0, Bullet.Speed - 50 * dt)

Manual deceleration. Clamp at 0 so the bullet stops rather than reversing.

Gravity Separate

Bullet has its own gravity setting that pulls down. Combine with horizontal speed for projectile arcs — cleaner than computing manually.

Drag Behavior

For air-resistance feel, add a Drag behavior or scale speed by 0.99 each tick. Tunable, doesn’t flip.

Verifying

Projectiles slow and stop as expected; never reverse unintentionally. Arc and trajectory match design.

“Acceleration compounds. For decel-to-zero, set speed directly with clamping.”

Avoid Acceleration for ‘slow down’ effects — explicit deceleration via Set Speed is clearer and bug-resistant.