Latest video from Dr. Airsoft with himself doing a spring change on an AEG and emphasises on the safety side of why spring changes should be done... "See the new Dr. Airsoft video demonstrating the quick-change spring of the Umarex H&K G36c by Ares. This system allows players to switch their muzzle velocity in just minutes, sometimes allowing operators to use a gun which would otherwise not be able to chrono under a field's limit. See also www.airsoftmedicine.com."