My Bersa Thunder 380 is the first and only firearm I've owned.
I am literally a gun-newb.
I'm no expert, though I like to take things apart and (try to) understand them, so i can share a coherent opinion, hehe...
I think...
You're all observing wear on the slide from contact with the disconnector nub on the trigger bar. It is just like the wear you'll see on the manual safety lever pivot from contact with the hammer release plate:
perfectly normal.
The Trigger Bar disconnector "gouging" the slide
The trigger bar has a disc-edged protrusion we can call the disconnector nub. (In BERSA literature the trigger bar is called the disconnector for this reason).
The disconnector nub fits into a matching slot in the slide above. Only when it's in the slot can the trigger bar function. In essence, it ensures that the trigger can only work when the slide is more or less in the correct position. When it's out of the slot, the nub drags along the slide's lip, producing the shallow track reported.
The trigger won't work without a mag inserted, right? That's because there's nothing to push the trigger bar up into the "active" position. BUT, even with a mag inserted, an out-of-position slide will push DOWN on the trigger bar, back into the "inactive" position. As the slide cycles, keeping the trigger bar pushed down, it gets worn by the trigger bar's disconnector nub.
I guess what I'm really saying is that the trigger bar gives way quite a bit, moving up or down, otherwise the wear on the slide wouldn't be so superficial. Even though the trigger bar is forged, and the slide I believe to be a rather soft investment casting, the wear is limited. The wear-track would have to become nearly as deep as the proper slot to affect function, and AFAIK there's just no way that can happen in 12+ years of respectable use --
work-hardening of the area metal would slow down the wear anyway.
The Hammer Release "gouging' the Manual Safety pivot
The hammer release plate also has a disclike edge, and it rides hard against the pivot/axle of the manual safety lever. The pivot however has a big notch built into it that (when in position) spares the plate-edge such contact.
Let's say you're cocked. If you switch the lever to SAFE, the notch rotates out of position, and there's the hard, full circumference of the pivot for the plate to deal with. The hammer release plate gets pushed violently down, disengaging the leaf-spring-like cocking piece down below, and dropping the hammer --although since you accomplished all this by switching the safety ON, there's no contact with Mr. Firing Pin, and what you've really done is DECOCK the hammer. Yep, that's what all this hammer-release chicanery is for: to DECOCK.
The contact in this case is much, much harder than in the previous case with the slide and the trigger bar, because the hammer release plate is working against more pressure from below....
However, the parts in conflict here are forged vs. MIM. Both very, very hard, and so there's less evidence of the violent contact. You can see it in the disassembled slide by switching the manual safety ON (SAFE), and looking for the wear track on the pivot/axle.
hth.
horge
PS:
Kokapelli (JF), can I request a photo of your Bersa and P3AT together for a size comparison? I'd like to post it on the gallery of the site if you're willing. PM me if so...