[Ron Wood]

I am doubtful that aluminum would hold up for a Luger receiver. In full recoil, the inertia of the receiver assembly is arrested by the recoil lug on the bottom of the receiver. However, the toggle assembly is moving independenly of the receiver. When the toggle is in full recoil, the rear-most portion of the toggle strikes the frame just above the lanyard staple, arresting the rearward movement of the breech block and toggle assembly. At that point, aside from the inertia that is taken up by the main spring, a lot of the force of the recoil is absorbed by that rear part of the toggle and the axis pin holding the toggle to the receiver. If you look at the rear toggle link as a lever and the axis pin as a fulcrum, you can see that a lot of force is placed on the pin in line with the direction and force of the recoil. I would imagine that it would not take long for the pin to stretch the soft aluminum, elongating the axis pin hole in the receiver and eventually leading to fracture of the receiver at that point. Just a guess, but I wouldn't want to be the shooter.