I have two DNA40 boards here installed and working perfectly that have the fire buttons snipped off by using flush cutting pliers. Both work perfectly. I just pulled one of the buttons that I had cut off out of my desk drawer and checked it electrically, the two legs on each end of end of the switch are connected internally. When the button is pressed all legs are connected. Note that with the switch installed on the board the pads on the lower side (towards center) are battery voltage and when the button is pressed the two upper pads are supplied with battery voltage. So I checked one of the installed boards with the fire button cut off, only the one lower pad (the one on the "out" side of board) had battery voltage. The two upper pads both became "hot" when my external fire button was pressed. So I think it would work just fine but from what I see with this 40 it would be the two lower pads that might be better if bridged. Heck, on my other one I think I cut off all three buttons......Flask clone.