Hoping for a little guidance, as I'm sure this isn't new, but my issue is complicated by having a second issue at the same time. I wouldn't be surprised if the two issues are unrelated, just coincidental.

First Issue:

I had two (that I'm aware of) blown primers today. Unfortunately, I'm not sure if they happened in the same rifle, as only one resulted in a malfunction (I think). My initial concern was any damage to the extractor(s) after they blew. Interestingly, both rounds were CBC 77gr MK262, which I haven't heard of issues with before (unlike IMI). The actual issue wasn't noticed until after all rounds were fired and I found two cases that showed blown cups.

Second Issue:

At some point today, my brass started having scrapes on the backside of the case from the lip towards center of the primer cup. I didn't really notice this until after I discovered an expended primer sitting on my shooting mat, but after looking at the other brass, not all of the brass had the mark, but enough of the brass had it that would indicate it came from both rifles (total of 50 rounds fired, across two different ammo brands). Here's an example of the mark (image is a little larger to help with rez to see the mark):



I disassembled and cleaned both bolts (one Fail Zero with 1300 rounds and one Colt with ~4000 rounds). Other than some gook on the extractors, they both looked healthy. So, think this is unrelated? Is this just the extractor slipping? If so, I have an easy fix, but first wanted to diagnose what might be happening.