These tubes are 1/4" in diameter. They will not fit your 556 and 223 calibers. Zerust ICT Tube and Barrel Strip beats gun oil hands-down! Our rust prevention Tube Strips are perfect for protecting barrels or lengths of stored metal pipes from damp environment. Tubes can be cut to length and is a narrow width (.250″ diameter) to fit any ferrous metal tubes and pipes. Just put the Strip into the interior of the metal tube, pipe, or barrel, and cap the ends. The air inside the pipe will be filled with VCI (Vapor Corrosion Inhibitor) formula that will dissipate when you uncap the ends. Zerust never leaves a residue, is non-toxic, and protects for up to 5 years.