The screw that holds the mag tube end cap on sometimes screws into the barrel.
If you have everything removed and are sure there are no screws holding anything in place a pair of vise grips (lined with leather) lightly clamped to the mag tube and then hammered on lightly will pop the tube out. Sometimes they bind from rust etc. at the receiver. DO NOT OVER TIGHTEN THE VISE GRIPS.
I don't need No stinking signature.