Alpo I see what you are saying so you start with a pump rebuild it and change it around so it is a full auto.
And now you have a gun that is not what it was but one that is what it is.
And that is not a full auto pump but a full auto shotgun in fact the only thing on it that is the same as the original is the mod. # and receiver and maybe the barrel.
All I could think about was staying out of the forarms way when it shoots