Slot 0 is used for vehicles. Vehicles use "playthread(0, sit);" when a player enters it. Since the minigun uses slot 0, sit will be replaced by root which makes the player go back to its default position. Usually weapons use slot 2, so use that instead.
Parent::onMount(%this,%obj,%slot);
{
%obj.playThread(2, root); //Attempting to make the minigun not force you to stand
}