ADVICE NEEDED, PLEASE: MCX causing excessive markings on fired cases I fired my MCX Partol in 5.56 (with Gen2 BCG) for the first time last week. I used Norinco 55gr FMJ ammo for the barrel break-in. I then noticed some strange markings on the head stamp of the spent cases (see the pic with 2...

I tried to search online for a parts list chart for a Sig P938, but couldn't find one. I'm wondering, what is the name of this part called and what exactly is it's purpose? I'm tired of it ruining my brass casings with a huge streak across the entire round. Yes I've tested it. I marked the...