4V50 Gary,
The way these are supposed to work, is that the action lock has a tapered face, that fits up against the rear of the bolt slide, which is tapered too. These will stay in contact, and not move, until the hammer falls, and trips it. However, they should not come apart, over friction, until the recoil from the gun moves the frame backwards, while you are holding the forearm stationary, which is actually giving the forearm a tug forward. That tug is enough to cause the separation of the two pieces, holding over friction (even if you were holding rearward pressure on the forearm, it will still tug forward). Since the hammer has fallen, it has tripped the spring that pushes the action lock down at the front. This trip spring shouldn't be strong enough to cause it to unlock, yet, unless it is fired, then recoil causes it, or the forearm is pulled forward a slight bit, manually, after dry firing.
If the action lock disengages during dry firing, without moving the forearm, then something is wrong, on the guns using the spring. If I recall, Mossberg guessed the rearward pressure from holding the forearm, would be enough to stop it. However, with no rearward pressure to the forearm, when holding the gun to the shoulder, with no spring, it is a possibility for it to come unlocked, since the friction is dropped between the slide lock, and the bolt slide. The trip spring pressure is then enough to cause disengagement, as soon as the hammer hits the firing pin.
The easiest test, to check for this, is to put the gun, butt down, on the bench, and apply some back pressure to the forearm, while holding it upright. Next, hit the trigger, and dry fire it. The action lock should not move, until the back pressure on the forearm is removed.
