I had bad scratches on the brass in my BCA rifle. I thought it was a rough chamber. It was actually from the sharp machined area in the thread extension, mainly the back two parts of the feed ramps.
I found this out partly on my own, and there are some threads here on the forum about it.
A simple test. Take an unmarred case and hand insert it into the chamber all the way in. Use a cleaning rod to pop it out.
If it is unmarked then it's a pretty good bet it's happening when the ejector is pushing the case to the right before it clears the barrel extension.
Dual parallel marks result from the case hitting on the sharp corners where the bolt head engages into the thread extension. You may be able to see brass marks in there where it's rubbing with a flashlight.
If this is what is happening in your firearm, the basic fix is to de-burr the sharp corners and machining marks as explained in past forum posts.
http://www.65grendel.com/forum/showthrea...ass+gouges
I found this out partly on my own, and there are some threads here on the forum about it.
A simple test. Take an unmarred case and hand insert it into the chamber all the way in. Use a cleaning rod to pop it out.
If it is unmarked then it's a pretty good bet it's happening when the ejector is pushing the case to the right before it clears the barrel extension.
Dual parallel marks result from the case hitting on the sharp corners where the bolt head engages into the thread extension. You may be able to see brass marks in there where it's rubbing with a flashlight.
If this is what is happening in your firearm, the basic fix is to de-burr the sharp corners and machining marks as explained in past forum posts.
http://www.65grendel.com/forum/showthrea...ass+gouges