5.56 AR reloading: Can Anyone ID what would cause these weird triangle shaped scrape marks/dents just below the shoulder?

[Bantam1]

Remember the bolt speed is much faster when it cycles than pulling it by hand. Try the deflector pad or soft sided velcro to see if it helps. If not you know its the extension and normal operation.

 

[WeR0206]

Remember the bolt speed is much faster when it cycles than pulling it by hand. Try the deflector pad or soft sided velcro to see if it helps. If not you know its the extension and normal operation.

Sounds like a good plan, thanks!