For hard use or milspec type duty, Id check the EO Tech sights. They are in use with many SWAT, DEA/ICE/FBI agents, spec ops.
Trijicon has the ACOG too. They are popular.
www.brownells.com www.midwayusa.com www.grafs.com www.cabelas.com www.natchezss.com www.cheaperthandirt.com www.uscav.com www.policehq.com www.deltaforce.com
I do all my own stunts.