Adjust The Aci Hornet Velocity

Tune the muzzle velocity of your ACI Hornet with a replacement hammer spring.

The Air Concepts Industries Hornet is a pump-action paintball pistol well-known for the accuracy of its factory stock barrel and simplicity of operation. Unlike more expensive paintball guns, the Hornet doesn’t include an adjustment screw or dial to control the CO2 pressure for each shot. If you need to tune down the muzzle velocity of your Hornet to comply with field rules, you must field strip the pistol and replace the factory standard hammer spring with a low velocity one. No tools are required, however, and the entire process takes only a few minutes.


1. Detach the gas cylinder from the ACI Hornet, if one is present, and remove any paintballs from the ammunition feed. Point the barrel in a safe direction, or at the ground, and pull the trigger to discharge gas from the system. Never work on a loaded or charged paintball gun.

2. Hold the front of the barrel in one hand and the pistol’s receiver in the other. Turn the barrel counterclockwise to unscrew it from the receiver. Pull the barrel free, and set it aside.

3. Remove the service screws that attach the pump to the receiver, by turning them counterclockwise with your fingers. The service screws are the two large, knurled screws that protrude from the sides of the flange on the pump handle.

4. Remove the knurled frame screws, located at the front and back of the trigger frame, by turning them counterclockwise with your fingers.

5. Pull the receiver assembly away from the trigger frame.

6. Unscrew the hammer/sear assembly and gas adapter from the back of the receiver, by turning it counterclockwise. Keep a firm grip on the assembly as you remove it, because it may be under pressure from the hammer spring.

7. Slide the factory stock hammer spring off the end of the hammer/sear assembly. Then slide the replacement low velocity hammer spring into place on the assembly. Apply a light coat of lubricant to the spring, then screw the assembly into the back of the receiver.

8. Reassemble the pistol by following Steps 2 to 6 in reverse order.