Machined aluminum components combined with a lightweight, carbon-fiber tube create a lightweight, durable extension to your shotgun. An extra-long spring is included that can be cut to optimize loading. Extension clamps are recommended for extension tubes that extend beyond the end of the barrel. To increase the capacity of the shotgun without having the extension tube extend beyond the muzzle, measure from the front of the shotgunâ‚¬â„¢s handguard to the end of the muzzle. This will provide maximum length.