I dislike the idea of milling a slot in the bottom of the barrel; if the nipple is not welded up, a person could load the gun conventionally and it would blow the stock to pieces when fired. Welding the vent hole on a flinter would be worse in the sense that it could be drilled easily without removing the barrel from the stock. Think in terms of a barrel secured by pins rather than a hooked breach and barrel keys. I think you would be better off fastening it to the wall with U-bolts, in a way they could not be easily removed. The basis of display for a functional gun is that they cannot be simply picked up, loaded and shot. If the lock had a V spring, it is a simple matter to remove it and the gun is more secure than a trigger lock. Keep in mind that a trigger lock can be broken apart with a screw driver, in seconds
cheers mooncoon