Is this normal and OK?

[Ahap]

Putting together a 6mm ARC AR15 with an upper that I bought complete, used. No fire yet, I just test chambered and extracted some rounds. This is factory Hornady Black 105gr, I was surprised to see that the projectile had engaged the rifling this deeply. Is this normal? I assume that's what these marks are, or is there a potential problem here? I intend to start loading for this round and others, but as of yet have never loaded anything. I do have an OAL gauge to find "jam" but haven't yet gotten a modified case for this round.

 

[NyleRN]

My humble opinion is that mark isn't from the rifling. Might wanna make sure the feed ramps on the barrel extension don't have a burr and see that the feed ramps on the barrel extension make a smooth transition to the ramps on the receiver

 

[Ahap]

My humble opinion is that mark isn't from the rifling. Might wanna make sure the feed ramps on the barrel extension don't have a burr and see that the feed ramps on the barrel extension make a smooth transition to the ramps on the receiver

I had that suspicion also. Further inspection needed.
Thank You

 

[bwframe]

 

[natdscott]

My humble opinion is that mark isn't from the rifling. Might wanna make sure the feed ramps on the barrel extension don't have a burr and see that the feed ramps on the barrel extension make a smooth transition to the ramps on the receiver

That's not a humble opinion. That's just telling the truth.

Unfortunately, barrel extensions are much more easily worked into elegance when not yet attached to the barrel..much less in the upper.

 

[natdscott]

Oh, and Ahap, read a lot and do a lot more research--or phone a friend--to learn how to judge jump/jam in the AR platform. It's not as easy as it is with a bolt gun, and the AR doesn't behave quite as gently if overfed.

Do these things, and your fingers will stay attached longer.

 

[Bassat]

Almost certainly not caused by rifling.

 

[jerzyperson]

When I built mine I had the same marks. It's from the feed ramp for sure.

 

[Cynical]

Oh, and Ahap, read a lot and do a lot more research--or phone a friend--to learn how to judge jump/jam in the AR platform. It's not as easy as it is with a bolt gun, and the AR doesn't behave quite as gently if overfed.

Do these things, and your fingers will stay attached longer.

Yep, it’s a rough and tumble ride into the chamber. I have some loads with .40 grain A-Max that shoot awesome out of a 20” 1-9 but they’re not crimped. Just good neck tension, I wasn’t willing to risk feeding them out of a mag.

 

[el_barto3]

View attachment 291851 View attachment 291852
Putting together a 6mm ARC AR15 with an upper that I bought complete, used. No fire yet, I just test chambered and extracted some rounds. This is factory Hornady Black 105gr, I was surprised to see that the projectile had engaged the rifling this deeply. Is this normal? I assume that's what these marks are, or is there a potential problem here? I intend to start loading for this round and others, but as of yet have never loaded anything. I do have an OAL gauge to find "jam" but haven't yet gotten a modified case for this round.

As long as the round fits the same in the chamber i.e. is the same length as the other cartridges (make sure the bullet isn't pushed in) then your good but I wouldn't toss a round like that, looks like it would shoot fine