Well, now I have to differ with Duggan on a few of his statements concerning the operation of pump shotguns!
Duggan says:" ... with pumps you have to load rounds in the tube, then pump, in order to accomplish the same thing" (in regards to loading a round in the chamber first so one can use it at need).
Also, " ... it works better then the pump way" (in regards to changing the shell in the chamber without affecting the shells in the mag tube).
I guess Duggan is not familiar with the Mossberg 500 action (also 590) that has been out there since 1961!
As to the first statement, the Mossberg 500 pump allows the shooter to actuate the Action Lock Lever (slide release) on the bottom left side of the receiver in order to slide the bolt to the rear and unlock the action. The shooter can then load a shell through the ejection port onto the shell carrier and slide the forearm forward to chamber a round. The shooter can then load the mag tube or not, as the case may be.
With the Mossberg 500 action, the shell in the chamber can easily be removed by actuating the Action Lock Lever and pulling back on the forearm to eject the round. If there are rounds in the mag and the shooter just wants to remove the chambered round, the Action Lock Lever can be pushed and the forearm pulled back slowly to bring the shell on to the shell elevator so the round can be removed. The bolt can then be pushed forward into battery on an empty chamber (or, another type of shell loaded to replace the one removed) without disturbing the rounds in the mag.
Additionally, the shells in the mag can be removed individually without removing the shell in the chamber by turning the action over so that the trigger is facing you. Place your thumb inside the loading port and depress the cartridge stop to remove each shell.
I also like the feature that the action can be put on safe at ANY time, even before any round is loaded. There are many shotguns without this feature.
I bring this up in the interest of being accurate. There is a reason the the Mossberg 500 shotgun is so popular besides price! They have to be good to be sold to LEO's, Military and civilians in the thousands each year.
I love all shotguns and have many in my safe, (M4 plus others). I have developed and will soon bring to market a new type of extended choke tube for shotguns (http://www.blackborechokes.com) if you care to look. I am not prejudiced against any type of shotgun, although I have my preferences.
GTP