That was evidently made to fit a washer or wad--probably a thin plate of soft metal which would be driven by the pressure from behind into the grooves of the rifling and thus give a spinning motion to the bullet.

When the latter left the barrel, the wad would drop off, leaving it free." "I see.

I was wondering what the square projection was for.

It is, as you say, extremely ingenious." "Highly ingenious," said Thorndyke, enthusiastically, "and so is the whole device.

See how perfectly it would have worked but for a mere fluke and for the complication of your presence.