JP Enterprises Silent Captured Spring9mm AR Short Stroke Version 5H5 Heavy The 9mm Silent Captured Spring is a drop in component that softens recoil and reduces cycling noise and vibration in your 9mm carbine. The result is a refined rifle that's a pleasure to shoot. Paired with our 9mm bolt assembly, you have the most reliable 9mm operating system available. The 9mm Short Stroke Version provides the same reliable buffering as our other 9mm SCS models but with a shorter overall stroke.