The frame cracks at the junction of spring tunnel and rails are the result of thin cross-sections and sharply machined corners. The cracks are more the result of flexing and vibration and they're self-limiting even in cast frames.
Parts tend to break where they're weak, not necessarily at the points where impact force is applied. The fact that the frames don't break at the impact abutments is neither here nor there. The impact causes the frame to flex and vibrate and that causes cracks in the locations that you describe (locations where cracks are likely to form as a result of the frame design).
The self-limiting aspect of the cracks is irrelevant, the question is whether or not their formation can be eliminated or at least discouraged by reducing the vibration and flexing caused by the application of impact force. It's great that they tend to not destroy the frame, but all else being equal, we'd all rather have uncracked frames than frames with cracks that are self-limiting.
But we're not talking about plastic. We're talking about steel.
It wasn't the plastic frames breaking, my understanding was that the issue was the steel locking blocks weren't holding up as well as the manufacturer intended them to. This was initially addressed with a redesign of the locking blocks and then finally with the Gen4 recoil spring.
By the time the bullet leaves the barrel, the assembly is so greatly decelerated by the bullet's delaying influence that the slide just isn't moving that fast.
The bullet's motion (along with the other ejecta momentum) is what generates the recoil. The slide will be moving as fast as conservation of momentum dictates it will, and all you need to know to calculate that is the muzzle momentum of the ejecta and the mass of the slide/barrel
Talk about the bullet's delaying influence is a red herring. Any delaying influence (assuming that any exists or even assuming none exists) induced by bullet friction can be TOTALLY neglected once the bullet exits because all you need to know to calculate slide/barrel velocity is the momentum of the ejecta and the mass of the slide/barrel. Any bullet/barrel friction will result in a slower bullet velocity and lower bullet momentum and that will, in turn result in a slower slide velocity. It's all ALREADY wrapped into the muzzle momentum.
You have a brick wall that you have to knock down. You have two hammers to choose from. A carpenter's hammer and a 10-pound sledge. Are you going with speed and energy...or mass and momentum?
Well, first of all, the carpenter's hammer has a much shorter handle and that means that the head speed will be much slower than the head speed of a long-handled sledge since head speed is also a factor of handle length, not just the angular velocity of the swing. That means it will have much less speed and mass and therefore much less momentum AND much less energy.
If we assume that the hammers both have about the same handle length, then a person of reasonable strength would be able to swing both hammers with roughly the same head speed. You would expect to get a faster swing with the lighter hammer, but probably not even a 2x improvement. For the heck of it, let's assume a 2x speed advantage for the lighter hammer. Since the head of the sledge is at least 10x more than the head of the carpenter's but the swing speed is only 2x slower, the heavier hammer head results in both more momentum (5x more) AND more energy (2.5x more) even though the head velocity is slower for the heavier hammer.
Basically, your problem, as stated, is meaningless because your assumptions don't follow. A typical carpenter's hammer doesn't have more velocity (due to the short handle) and certainly not more energy than a typical long-handled 10lb sledge. The 10lb sledge wins in every category. Even if we try to even things out with similar handle lengths, a long-handled carpenter's hammer still probably won't have more energy because you'd have to be able to swing it more than 3x faster to compensate for a 10x advantage in head mass that the sledge has.
