The photos show the custom sleeve on the right compared to a standard factory sleeve on the left. The custom sleeve is chamfered on the inner edge of the valve side to smooth air-flow. The inside diameter is about .150" to match our Magnum Valves. Compared to a standard steel sleeve, it increases air-flow for more power and better shot-to-shot consistency.
With standard Discovery, 22XX and 13XX valves, this custom sleeve helps compensate for misalignment of the ports. This is often caused by the valve-port hole in the tube being out of alignment which seats the gasket off-center to the valve port.
It fits 1377C, PC77, 1322C, P1377, P1322, 2289G Backpacker, 2240, 2250B, 2260, 2300T, 2300S, Benjamin Discovery, Crosman Custom Shop and related models.
It will not fit older 1377, 1322 or similar models that have a sliding breech cover.