Absolutely unusable - Adams Arms Standard Picatinny Block Piston Kit

Will not work on s&w m&p15 could not get supplied bushing in without tool come to find out it is not needed,bought a full floating handgaurd to replace the factory delta ring style now the return spring binds and clearance issues in the piston end I get no response from optics planet,should have bought a complete upper,would have been cheaper with less headache