Maxim Defense Industries JP Silent Captured Spring - Heavy Grey/Black. Choose from the standard/carbine weight heavy weight and 9mmweight Silent Captured Spring Systems. The JPSilent Captured Spring Systems require an open channel in your bolt carrier group assembly for the guide rod to pass during fire. Note:DO NOT MODIFY A BCG TO MAKE IT COMPATIBLE. DO NOT REMOVE THE WEIGHT FROM 9MM BCGS. JP DOES NOT RECOMMENDED FOR SELECT FIRE. Specifications for Maxim Defense Industries JP Silent Captured Spring: Manufacturer: Maxim Defense Industries Color: Grey/Black Fabric/Material: Tungsten and Stainless Steel Condition: New Country of Origin: USA Package Contents: Maxim Defense Industries JP Silent Captured Spring Maxim Defense Industries MXM-47571: JP Silent Captured Spring - Heavy Grey/Black