Thumb C Liquitron Tons and tons of mods for Nerf toys, guns and accessories. A sample…SuperMaxx 750 PETG barrel replacement mod: My goal was to replace the stock barrel on the SM750 with 6″ x 1/2″ PETG tubing and increase the working pressure of the air system. The barrel material is very difficult to find and can be replaced with 9/16″ OD K&S brand brass tubing for very similar performance. Link.