[Ron Wood]

Ed,
The toggle action does not work by itself. In essence, it is thrown backwards by the speed of the barrel/receiver in recoil. As the barrel/receiver moves to the rear, the toggle knobs strike the frame "ears" and move upward unlocking the toggle links allowing the breechblock to move independently of the receiver. The lug on the bottom of the receiver stops the rearward motion of the barrel/receiver but the speed of the movement to the rear gives the toggle train the inertia to continue its rearward motion.

The longer barrel may give the bullet a bit more velocity, but it is only a small increase. The barrel on this Luger is huge in comparison to the standard barrel or even a carbine barrel. Not to get too technical, force is equal to the mass of an object times its velocity. You have a very small mass (the bullet) times a small increase in velocity. This is nowhere near enough inertia (force) to overcome the greatly increased mass of the heavy barrel. Given one of Newton's laws that for every action there is an equal and opposite reaction, the heavy barrel has upset the balance required to cause the action to function properly.

The force imparted to the barrel/receiver by the bullet (action) is only marginally improved by the increased velocity derived from the longer barrel length. But the mass of the barrel/receiver is greatly increased by the heavy barrel thereby reducing the effect of this small force. So the rearward motion (velocity) of the barrel/receiver (reaction) is proporionally reduced. This slowing down of the rearward motion results in the failure of the action to cycle properly. That is why the original carbine rounds were loaded "hotter" and the forearm had an accelerator spring to help return the action to battery. The 1920 carbines eliminated the accelerator spring by employing a heavier mainspring, but it still required a heavier load and the barrel was considerably lighter than the bull barrel on this gun. Weakening the spring will let the barrel/reciver group move to the rear faster, true, but then there isn't enough spring "energy" to return the action to battery.

Bottom line is that unless magnum loads with a heavy spring are used, it isn't going to cycle properly. The firing pin spring has virtually no effect.