A bullet is softer than steel so I doubt a bullet has upset steel. Quite possibly this is a build up of fouling. Try scrubbing with JB Bore Cleaning Paste on a tight patch...
Hi guys, is there any way to make this better? The bullets have mushroomed the land after the gas port. I would think it's messing up the bullet on its way by.
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AR-15s are well known to suffer erosion on the downstream side of the gas port. It's not caused by impact or fouling, it's just the swirling of the hot gases associated with the hole.