I took my Vector V53 SBR out today for a quick range trip. It had recently been having a lot of FTE issues and after giving it a full breakdown and cleaning I wanted to try it once more before I changed the extractor spring.

The FTE problem was solved but I noticed that some of the spent brass had very deep marks on it from the fluted chamber. Even one the flute marks were so deep that they almost cut through the case. It looks like signs of over pressure or something similar. I was using standard Federal XM855 greentip.

Does anyone know what could be causing this or if it's a problem?

I have a V53 and it marks them with a whimsical design, but not any type of cutting or deformation.  

Can you post a picture of the brass?

I saved the brass. I'll be away for the evening but I'll snap a picture of it tomorrow and post it. It usually marks up the brass a bit but this time it was way worse.

Check your bolt gap as well.

My vector 53 is the same thing when I combined my sear with a can. After a little research, it seems my locking piece was a modified one, reground by vector.

I replaced it with a real HK, for the correct bullet weight and the problem disappeared.

I reload so almost all of the ammo I shoot in my V53 are mid-range blaster type loadings in terms of pressure & velocity. I don't have the sort of brass flow issues you're describing in my guns chamber, just the classic carbon skunk stripes.
I'd suggest another brand of ammo and see if this continues as it sounds like a pressure related problem to me. I have seen brass flow into the flutes with some hot 9mm loads in a friends HK SP89 which created some real extraction problems, these rounds have been sidelined because of this.
I have had some case separation issues with once fired Federal brass in various guns which makes me think their brass is a bit soft and prone to elongation but again thats just my gut feeling.

Here's the picture of the worst one I could find.  If you look down inside the brass, you can see daylight coming through some of the flute marks.  This gun has always marked up the brass pretty good, but I've never noticed it being this bad.

Yikes.  

I agree with the other two posters that this is a pressure related issue.   I would try a real HK locking piece as suggested first (cheapest and easiest), and if that doesn't remedy it, I would recommend you engage Vector.

I think it might have been a bad round that was overloaded at the factory. I took the gun back out yesterday and fired some more of the Federal XM855 as well as some Danish M855 through it, and there were no spent cases that had deformation as bad as the one I pictured above.

The Danish stuff just had the usual carbon marks, and Federal had some indentions in the brass but nothing nearly as bad as before.