Check the listing for details. AMG High Output Valve for UMAREX VFC M4 GBB. Condition: New. Listed at 12.00 USD. The AMG High Output Valve (Gen II) is a high-quality and reliable accessory designed specifically for the UMAREX VFC M4 GBB marker. This valve enhances the performance of the marker by regulating the airflow and providing a smooth and consistent output. With AMG's reputation for producing top-notch products, this high output valve ensures that your marker operates at its best, making it ideal for outdoor sports enthusiasts and hobbyists looking to improve their paintball experience.