Hi guys, like the title says. I know how to do the forward assist on a normal ar-15 but can't figure out how to do it on the lightweight LR 308 upper. I put the pin in from the top and the forward assist just locks stiff and you can't move it. I know on the ar-15's you put it in from underneath but i'm not seeing how that's possible on the LR 308 upper. Can anyone help?