I am a newbie. Recently acquired this 1860 Colt by Armsport. Never Fired all Stainless. A very nice revolver. This appears to be what some refer to as a 4 screw frame. Is that Correct? What is that fourth screw for? The parts breakdown that came with the gun (my DI would have my a**), is generic for a " Colt Pony Express - Navy 1851 - Army 1860" and does not make any reference to that screw. The gun is pretty clean but want to strip it down before firing this week, hopefully tomorrow. This is really a nice revolver. Not familiar with Armsport but the workmanship is outstanding. Can't find any marks to indicate date of mfg.