Most semi-autos get that from ejecting brass - Hoppes will usually take them off.
Be aware that if you shoot aluminum cased ammo - there is no way to get these off. I prev had them on my USPc slide from the aluminum cased ammo. The stuff that takes off the brass marks won't work on the aluminum marks.
Everytime I shoot the gun, however, you will just get more.
The slide on my Beretta PX4 is inset a great deal around the extractor area. So, it doesn't get these marks.
Also, with my slide being hard chromed, I no longer get these marks on my P99, P99c and USPc.
So far I've tried Hoppes #9, Hoppes Elite Bore Gel and Break-Free, and no real luck. Is there anything beyond wiping it on, letting it sit for a few minutes and then wiping it off to try?
I've seen it suggested elsewhere to leave a patch saturated in Hoppes (presumably #9) sitting on the mark for several hours, but I'm a little nervous about messing up the finish on the gun. This has gotten slightly more urgent as I managed to mark the back of the slide with a brass coat button while practicing this week . Nothing too awful, but it's distracting when I'm looking at my sights.
I don't understand the problem here, unless there is something peculiar about the PPS's finish. In more than a half-century of shooting autoloaders I've never seen a brass ejection mark that could not be removed with Hoppe's No. 9 and a little scrubbing.
This may sound nuts, but a bronze bore brush is hard enough to remove even a stubborn heavy brass mark, but will itself leave a coppery wash on the surface. However, that in turn is easily removed with Hoppe's, and the whole thing comes out clean, fresh and smelling like a gun should.
Want to Necromance this thread... I shot my PPS for the first time today and had the brass marks around the ejector port, like everyone says is normal. However, my brass markings are on the front side of the ejection port, on the top of the slide. Everyone I have seen as normal is the lower left of the ejection port (where my P99C got them). Should I be concerned? Seemed brass was being ejected about three o'clock, not more 5 o'clock like other guns.