Should I be worried about this?

Welcome Scrod314!
I can't tell what that is. Is it a crack, or just a scratch?
If it's a crack, I'd be really worried about it. If it's just a scratch, not so much.
Whatever it is, I compared my wife's Shield to the picture, and she doesn't have anything like that on hers. Do you know a gunsmith that you can have take a look?

Welcome to the forum, from what I see it looks like a scratch from rubbing on something like a burr on the top inside of the slide. Have you inspected the slide for anything the barrel may be catching on? Maybe the barrel had some minor excess finish there that got knocked off. Run a q-tip along the inside of the slide to see if it catches on something? My shield 45 shows nothing like that.

Wouldnt sweat it. Welcome to the forum!

Welcome! Nice job on looking up a question about safety. Happy shooting!

This what happens when you actually shoot them.

That’s just a birth mark

Sounds like you got a nice deal. Holster would be pretty much useless for me here in NJ, but 300 rounds added in is great (especially during these times). Good luck and safe shooting.

That may be where the slide is contacting the ejected cases as they emerge from the ejection port. That's normal, and prevents the ejected cases from coming directly back at you.

Hummm. And all this time I thought it might be flame cutting.

Ditch the One Shot snd use a quality oil or light grease.

Hit that mark/stratch with a black sharpie and see if it happens again.

Welcome!
Many semi autos get wear marks on that portion of the barrel. The fit of that squared portion of the barrel serves as the locking mechanism and is a location of high stress and rapid movement as the barrel unlocks and cams down an instant after firing.
Almost all of my blued guns similar in operation to the shield show bluing wear in this area. Since yours doesn’t seem to have a burr or high spot on the underside of the slide, or at that location on the barrel, it is probably just a result of the firing-wear pattern of your particular gun.

Stay safe.

Scrod314 said:

Hello... My first post. I've put about 500 rounds through this Shield 40 and noticed this. Gun functions fine. Any thoughts?

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That there is called a wear mark. You find these in pistols that have been loved by there owners.
It’s just the pistol fitting itself.

Congratulations on your first one.
Here’s to many more, friend!

Welcome to the forum, nice Shield 40, Scrod314! My son has an SD40VE.

You from Boston by chance? Scrod is some fine eating!

Here are the same locations on an LCP .380, an LC9 9mm and a Glock 34 9mm.





All have some wear on the same portion of their barrel on the top of the chambers.

Stay safe.

LOL!

The Bushmaster said:

Hummm. And all this time I thought it might be flame cutting.

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Scratch. Carry on.

Looks like you have things figured out.....but lets not be hasty. Do you WANT to worry about it? Jesus said to "be anxious for nothing". That mark is really close to nothing so it might be a suitable worry candidate.

Kudos to you for being so observant. Attention to detail matters. Glad you got it figure out. Me, when I am not sure - I go to a local smithy for a look-see. But your picture was great!

A good method in playing the "scratch or crack" game on firearms is try to get a light behind it. A small bore light will fit into many tight places. Put the light behind the supposed crack and heat up the outside with a hair dryer or low heat gun. Heat will expand metal parts making the light through a crack easier to see.