I bought a Big Guns machine recently that did not come with a back box key. I think the the back box locking bar is keeping the back glass from sliding into place properly. Could someone describe to me how the back box lock works on a Williams System 11b please? I am not familiar with it. I think the bar is laying right where the glass needs to fit and is just enough to keep the glass from fitting properly into place. I want to confirm before I drill the lock out and replace it.