Universal Heavy bolt for Gas Blowback Rifles. Recoil kicks like a mule, solid steel bolt imported form overseas👍 Have been tested in: •WE-tech M4 •Western Arms M4 •G&P WOC M4 •GHK M4 Works great and is definitely an upgrade to real kick with gas rifles! Some modification might be needed as not all rifles are the same. Selling for $50 shipped