Decent product may require tweaks - Adams Arms Standard Picatinny Block Piston Kit

Pretty decent set up and install. You will have to watch what handguard you use. Some free floats will not work due to barrel nut or if not exactly or under 9 inches for midlength. If using a two piece drop in you'll have to either trim up or order one of their end caps. Used a b5 drop in and had to trim up the ends to alow gas system to fit.