Semi auto shotgun

So i have a winchestet sx4, it came with a plug in it to make it only take 2 2 3/4 shells in the tube, i took the plug out and now it holds 4 in the tube, one in the chamber 2 3/4 shells. So my question is, is it legal? I realize that if i wanted to buy short shotgun buckshot rounds i could fit a lot more than 4 in the tube but idk if it would even run those shells. Im thinking that it is legal because it has 4 in the tube when its at home but just wanted to make sure.