Silverback Airsoft shows the increased effect of the TAC41 Sport Hopup Shims... "Out of the box, the Sport version of the TAC-41 is equipped with a hopup preload adjustment system. The hopup TDC wheel have a 750µm travel, and you can add preload by removing 2 shims under the hopup wheel. The small shim reduce the hopup preload, and the big shim catch back the Oring pressure to stabilise the hopup wheel. Both shims should have the same thickness. If you are willing to increase your hopup effect, you can remove both shims. WARNING: without the shims, you may face some jams with strong hopup setups."