Cleaning a needle bundle type pneumatic rust removal gun can be a bit tricky, but here are the general steps you can follow:

Disconnect the gun from the air supply and make sure it is completely depressurized before starting to clean it.

Remove the needle bundle from the gun. Depending on the design of your gun, this may involve unscrewing a cap or removing a retaining clip.

Inspect the needle bundle for any signs of damage or wear. If any needles are bent or broken, replace the entire bundle rather than trying to straighten or replace individual needles.

Soak the needle bundle in a rust dissolver or mineral spirits to loosen any rust or debris that may be stuck to it. Follow the manufacturer's instructions for the specific product you are using.

Use a small brush or toothbrush to gently scrub the needle bundle to remove any remaining rust or debris.

Rinse the needle bundle thoroughly with clean water and let it dry completely before reassembling the gun.

Reassemble the gun, making sure all components are properly aligned and tightened.

Test the gun to ensure it is working properly before using it again.

Remember to always wear appropriate personal protective equipment, such as gloves and eye protection, when cleaning pneumatic tools.