Freaky looking, huh?
Yeah, I called back in a mild panic to discuss it with a tech the first time I saw this on a brand new 4513TSW.
(I was inspecting a gun from a new shipment of .45's and saw this on one of the 4513TSW's.)
I was told that the "break" was actually intentional, and had just started being done to relieve a thin spot in the ejector depressor plunger channel (at the rear), next to where it intersects with the firing pin channel cut.
It was further explained that the shape of the nylon plunger, with its added side ribs, resulted in this thin spot where the plunger's
rear rib needed to move up & down freely. Not much steel behind that cut for the plunger's rib to move within. (The round firing pin safety plunger on the
other side of the firing pin channel doesn't have an added "rib" protruding to each side, so the plunger channel cut is thicker in the corresponding spot at the rear of
that cut.).
The engineers had apparently observed that this thin spot could sometimes eventually crack under recoil. I was told that it's not a critical spot for the crack to form, with the rest of the plunger being normally supported within its recessed cut. (Note the way the plunger tip is contained within the rest of the normal machine cuts. It's not as "unsupported" as it may appear at first glance. The "rubbing" or "drag" marks on the bottom of the plunger are commonly caused by the ejector's movement underneath the plunger, some of which have some variable smoothness along the edges.)
Rather than leave it to normal wear & tear to eventually "break" the thin metal from the intersecting machine cuts, though, they decided to start knocking out the metal where the crack could form. Pre-breaking it, so to speak.
This bit of newer machining to relieve the stress in the thin part of the slide at that spot isn't even really a cosmetic issue, as the manual safety assembly has to be removed in order for it to be revealed. (As you've discovered.
)
After my conversation with the factory I checked a couple other new production 4513TSW's received, and sure enough, I found the new guns had the same "break" and "missing" piece of metal.
I was also told that this machining step was planned for the rest of the new TSW guns as production continued.
This isn't the first time something like this has occurred, BTW.
One side of the disconnector cut in the bottom of the slide is thinner than the other side due to machining and an intersection of cuts. It often (eventually) resulted in a thin triangular steel "flake" breaking loose under recoil. I was told that it usually fell free of the slide during cycling, which let it fall free of the gun without the shooter even knowing it happened. (This triangular spot on one side of the disconnector notch is now "open" on newer production slides, as newer manufacturing methods can remove it.)
The rear of the thin machined cut underneath the extractor recess, on the right side of the pick-up rail in older 9/.40 slides, could sometimes develop a curved crack, running from the end of the cut to the side of the long channel along the right side of the pick-up rail. The metal connecting the "top" of the slide channel on the right side of the pick-up rail, and the bottom of the extractor recess cut above it, was VERY thin at that spot. Recoil forces could easily let the resulting thin piece of metal develop a crack, which ended as soon as the thicker metal was reached on the outside of the long channel.
Sometimes this "crack" would result in the thin piece of metal between the end of the machine cut and the edge of the long channel breaking off and falling away. It wasn't very large. Sometimes the "crack" relieved the stress and the thin "floor" of metal connecting the bottom of the extractor recess and the long channel remained in place. Not critical, but it could be a minor cosmetic surprise to an owner/user finding it during cleaning.
Newer machining methods allowed them to make better cuts that eliminated the potential spot for this sort of stress riser to occur.
Another occasional spot for this sort of thing was in the front of the early 645/4506/4506-1 slides, at the rear of that thin metal tunnel connecting the barrel and the spring box. The machining of that thin metal sometimes allowed for what looked like a chunk of "missing metal", a large "crack", a break, etc. It was actually intentional, and necessary for the easy removal & installation of the barrel during field-stripping. They called it something like a “4 degree free cut”. It could look nasty, though, and still freaks out the occasional owner who notices it for the first time.
Later machining methods allowed for a better bevel cut in that spot.
So, unless something's changed since my last armorer update/recert, and my conversation with the tech (close to 5 years ago) when I found the same thing and did a double take, the picture you posted looks like the other new production 4513TSW's I've seen.
Just my thoughts. Feel free to call back and try to get a tech on the phone. Don't be surprised if you hear a good-natured chuckle, and something along the lines of, "Oh, you found that, did you?"
