Unless there is a poor sear engagement on the second barrel that is set off by the other trigger movement, then there is no such thing as a true doubleing, a true doubleing is two shots similtaneously fired, as by pulling both triggers! What most call doubleing, is however, a very quick one, two shot, and will not damage the rifle in any way! By the time the second barrel fires, the peak pressure of the first one has eased, and this is exactly like fireing two shots in the normal manner, but quickly. Why the so-called doubleing gives the elusion of more recoil is, the second barrel fires while the rifle is in the recoil arch. If this happens whilt the rifle is pointing at a very large target, at close range, the first barrel will print where you are shooting, but the second barrel will print very high,sometimes shooting over the target all together, because it was actually fired much later than the first. All this happens so quickly, that it seems similtaneous,to the shooter, but it isn't!

If the 1,2 shots are caused by the worn sear engagement, it needs fixing, by a good gunlock smith!