I am sure clapper is referring to using a thin rectangular punch at the end of the for-end iron slot adjacent to the barrel for- end catch. By moving metal with the punch it removes the play between the barrel catch and the for-end iron slot. This method Jack Rowe demonstrates is the method preferred rather than removing the play by welding and all that goes with it re-bluing etc. It does come over as a sort of second rate repair but you would be surprised how many older guns have been repaired in this way.