MAS Defense LLC "Quality Parts at Reasonable Prices!" Established 2013 Building, modifying or upgrading your firearm should be both fun and hassle free. We are here to make that process as easy and enjoyable as possible. We genuinely care about your needs and it shows. Our first-time customers continually become our long term customers time and time again. Shoot us a e-mail to Support@MASDefense.com to discuss your plans. We look forward to serving you! Thank You, MAS Defense LLC