AR-15 Markings on Bullet

[Mlapor3]

A friend had assembled a lower and bought an upper for the rifle. After manually cycling some ammo for a basic function check, we looked at the ammo and discovered scratches on the bullet itself in a parabloic shape on opposing sides of the bullet. Is this normal? What could be causing this?

The upper had M4 feed ramps cut in it and my first thought was that something had a bur but after feeling around I couldn't find anything.

Any help is appreciated.

 

[Sin-ster]

Have you got any pictures, by chance?

How deep are the scratches?
Are they perfectly mirrored on both sides of the projectile-- i.e. exactly opposite?
Do they curve from tip-to-tail, or back-to-front?
How far down the projectile do they start, and where do they end?

As you suspect, the feed ramps can cause marks on the projectile as they are fed, even without visible/tangible burs. It's most likely when the rifle is new; you'll get some burnishing/polishing/filling in as you shoot it.

Equally likely is that the projectile is getting buggered as you're extracting it. It can knock around the barrel extension, or more precisely, drag between two of the lugs as it's coming out of the chamber. This would be my guess, as you're reporting uniform marks on what I assume to be perfectly opposite sides of the bullet.

If they're not very deep, you probably won't even see accuracy fall off with those rounds. They'd have to be catastrophic to be unsafe to fire. IOW, I wouldn't worry about it too much, no matter what the cause is.

 

[SpeedRacer]

I wish they would pass a law, on the state or federal level, that required firearms actually be shot before trying to diagnose "problems".

Verify safeties work properly at home, verify function at the range!

 

[Mlapor3]

Scratches are fairly shallow. They are on exact opposite sides of the bullet in a parabolic shape with the vertex of the parabola towards the tip of the round.

Unfortunately I do not have any good pictures of the markings as I was unable to get my iphone to focus on something that close. The scratches start about 1/8" from the tip of the round.

Thanks for the help guys.

 

[rrussotwo]

I wish they would pass a law, on the state or federal level, that required firearms actually be shot before trying to diagnose "problems".

Verify safeties work properly at home, verify function at the range!

I wish we had a "like" button on BS.

 

[Sin-ster]

Yeah, 3:1, you're getting the marks during the extraction of the live round as it's dragging between two of the lugs.

Look into the barrel extension with a light and see if you can spot some copper washing on the lugs-- probably the two closest to the ejection port.

Also try to eject a cartridge very slowly, ensuring to extract the round straight out of the chamber without contacting anything on the way. See if that bullet has the same markings.

If they're shallow, they're not going to cause you any problems no matter how/when they're appearing on the projectile. And if it's something that's happening during feeding, it'll stop eventually as the gun is run in. I do understand your curiosity, though.

 

[robbynola]

1

 

[Sin-ster]

Just... wow.

Don't sweat the hate, OP. Shoot, I'm just happy for a question that isn't the same mindless "which gun is betterz", in which the poster totally ignores the best advice anyway...

 

[Leadfoot]

Parabolic shape with the vertex pointed toward the... Are you ****ing shitting me? This is what pics are for.

And yes, it's normal. When you extract a live round, the locking lugs scratch the projectile. No, it doesn't hurt anything. Yes, the round is safe to use. No, it won't effect accuracy in any meaningful way unless perhaps if you're doing some sort of extra long range work.

I love the enthusiasm, man. Seriously. +1

 

[JLouv]

Just... wow.

Don't sweat the hate, OP. Shoot, I'm just happy for a question that isn't the same mindless "which gun is betterz", in which the poster totally ignores the best advice anyway...

+10 on everything. Especially the first part, the middle and the end.

 

[Mlapor3]

Sin-ster, thank you for the helpful replies. I certainly appreciate the help. We have a range trip planned for next weekend. I'll report back with any issues.