They could have bolt bounce issues like true machineguns do. There can also be issues with timing Should the "M16" bolt copyright or other areas are slightly out of spec. All troubles that occur up on machineguns but are invisible to semi auto shooters. Yeah I saw that GMR posted https://forcedresettrigger45678.tokka-blog.com/36545269/rare-breed-frt-trigger-for-dummies