I can't help but imagine it slightly different. The bank robber responds: Wait, don't you mean it chambers the most powerful handgun cartridge?
Harry: Well, you have a point...
Robber: Wouldn't the powerful handgun be something like the Colt Walker, which took 60 grains of powder in each chamber?
Back up arrives to find Harry & the robber deep in conversation over what defines the most powerful handgun.