The JBU M4 Kurz Conversion Kit is the ultimate M4 CQB Conversion. This kit comes with a short free float rail system with a matching barrel and Kurz barrel extension. Also included is a JBU 6.03mm tight bore barrel and delta ring tool for extreme accuracy and easy installation. All of the pieces in the JBU Kurz Conversion Kit are made of high quality metal for long lasting performance. There no other kit better suited for a CQB type M4 than the JBU Kurz kit.