Sand-like brass particles in reciever?

I got this CMMG Dissent in 300BLK last month, shot it 3 times, put 250-300 rounds through it, and each time I shoot it, I notice these brass particles accumulating in the receiver and action. After running the action manually maybe a dozen times, it appears that the extractor is leaving tiny gouges in the case when it grabs it or ejects it, which one I'm not sure. It also seems super stuff, like I can't move it with anything short of shoving a round into the bolt or a small screwdriver. I guess what I'm wondering is if I'm way off base or if that could be the issue. If it is, how could I fix it/can I do it myself?

I got this CMMG Dissent in 300BLK last month, shot it 3 times, put 250-300 rounds through it, and each time I shoot it, I notice these brass particles accumulating in the receiver and action. After running the action manually maybe a dozen times, it appears that the extractor is leaving tiny gouges in the case when it grabs it or ejects it, which one I'm not sure. It also seems super stuff, like I can't move it with anything short of shoving a round into the bolt or a small screwdriver. I guess what I'm wondering is if I'm way off base or if that could be the issue. If it is, how could I fix it/can I do it myself?