Feeding Ramp scratches bullet copper jacket

jxh5760

New Hide Member
Sep 20, 2018
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#1
so just go this new 6.5 CM AR10. With Hornady 140gr ELD match.

When I load and extract a live round, I see there are scratches on the copper jacket, and also there are traces of copper on the feeding Ramp left behind.

I think I can even see the lead core!https://photos.app.goo.gl/25tRhPn4g4HEbPgG8

I've seen other posts about this and people always say this is due to extractor pushing the bullet against the inside of barrel. But how about the copper on the feeding Ramp?
 

hookedonbrass

Sergeant of the Hide
May 16, 2018
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Virginia
#4
not sure. mine is scratching more the case. i can see it on my spent cases, two deep scratches at the mouth that are the same distance apart as the feed lips.

rifle is decently accurate. can't say whether my occasional "flyers" are due to that or any other number of variables with an AR platform assembled piece by piece.
 

jxh5760

New Hide Member
Sep 20, 2018
5
0
1
#5
not sure. mine is scratching more the case. i can see it on my spent cases, two deep scratches at the mouth that are the same distance apart as the feed lips.

rifle is decently accurate. can't say whether my occasional "flyers" are due to that or any other number of variables with an AR platform assembled piece by piece.
Thanks.
 

Mooncake

Sergeant of the Hide
May 29, 2018
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Central Mountains, CO
#6
My two LWRC REPRs were marring the crap out of bullet jackets until I took a polisher (dremel) to the inside of the chamber. There may be a feed ramp that extends from your chamber lugs that is sharp. If you haven't yet, feel around with your finger. In the REPR, it came to a point that I was convinced was the culprit. After polishing to the point where it didn't stick my finger, the jackets were no longer so F'd up. I can still see a light mark on the bullet from feeding that is probably unavoidable but it doesn't lend the impression that it's going to effect flight so profoundly. It improved group size quite a bit, although I don't have any empirical data to share.
 

jxh5760

New Hide Member
Sep 20, 2018
5
0
1
#7
My two LWRC REPRs were marring the crap out of bullet jackets until I took a polisher (dremel) to the inside of the chamber. There may be a feed ramp that extends from your chamber lugs that is sharp. If you haven't yet, feel around with your finger. In the REPR, it came to a point that I was convinced was the culprit. After polishing to the point where it didn't stick my finger, the jackets were no longer so F'd up. I can still see a light mark on the bullet from feeding that is probably unavoidable but it doesn't lend the impression that it's going to effect flight so profoundly. It improved group size quite a bit, although I don't have any empirical data to share.
Thank you! That's really helpful!
 

padom

SuperMod
Staff member
Mar 13, 2013
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Southeastern, Pennsylvania
#8
Polishing wheel on a dremel. The barrel extensions inside edges are sharp and need to be polished. You need to clean your barrel extension/barrel thoroughly after doing this cause your removing metal. JP recommended this a few years ago and even instructed what attachment to use on your dremel.

This is why I use JP QPQ extensions on my custom barrels now, they are honed and nitrided.


Dremel 520-02 SIC Impregnated Wheels (2 Pack), 1/2" https://www.amazon.com/dp/B015PK3DKI/ref=cm_sw_r_cp_apa_U.cPBbN1N62MA
 

jxh5760

New Hide Member
Sep 20, 2018
5
0
1
#9
Polishing wheel on a dremel. The barrel extensions inside edges are sharp and need to be polished. You need to clean your barrel extension/barrel thoroughly after doing this cause your removing metal. JP recommended this a few years ago and even instructed what attachment to use on your dremel.

This is why I use JP QPQ extensions on my custom barrels now, they are honed and nitrided.


Dremel 520-02 SIC Impregnated Wheels (2 Pack), 1/2" https://www.amazon.com/dp/B015PK3DKI/ref=cm_sw_r_cp_apa_U.cPBbN1N62MA
THANKS!!
 
Aug 14, 2014
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19
8
#10
You can use a long handled Q-tip to get where your fingers can reach. See if there are any places that drag cotton off the swab or feel rough. You can use Flitz polish on a Q-tip as well for places that a Dremel attachment won’t fit. Go slow because the polish is removing material. Don’t spin a Dremel up to ludicrous speed and go forever.
 

padom

SuperMod
Staff member
Mar 13, 2013
6,653
652
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Southeastern, Pennsylvania
#12
When cartridges are pulled from the chamber the ejector pushes the case to the right in order to flip the case out of the ejection port. As the cartridge exits the chamber it is drug across the corners of the barrel extension lugs. It causes 2 fang marks about 1/8" apart lengthways down the case and bullet.
A properly honed/polished barrel extension will not do that. I learned my lesson with these deep, nasty gauges and scrapes on my first custom 6.5cm AR barrel many moons ago using a BAT extension that wasnt cleaned up. You can stick your finger in there and feel how sharp the back of the locking lugs are. JP's honed and nitrided extensions are smooth as butter out of the box.

You are correct, the lugs from roughly 2 o'clock to 4 o'clock are the ones you need to concentrate on. You can also clean up the ones from 4 to 7 o'clock if you think they are being scratched on insertion but its typically on extraction.
 

Fig

Janitor of the Hide
Mar 15, 2018
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#14
I could be wrong, but from the OPs pictures I'm quite sure the rifling down the barrel scratches the jacket quite a bit more than that, and I would doubt it would affect precision noticeably (it IS a gas gun).

From shooting some deformed bullets, just to see what would happen, I've found that the nose could be damn near folded over and it would fly straight, but any deformity to the boattail, heel, or base would screw precision. It wasn't a scientific study, and I can't claim it's repeatable, but I shot about fifteen rejects that were deformed and got good precision out of all of them except the ones were the deformity was on the rear of the bullet. Those were invariably fliers.
 

padom

SuperMod
Staff member
Mar 13, 2013
6,653
652
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Southeastern, Pennsylvania
#15
I could be wrong, but from the OPs pictures I'm quite sure the rifling down the barrel scratches the jacket quite a bit more than that.
Edit:
After reading your post a few times I now see your trying to say the rifling scratches the bullet more than that when fired. At first I thought you were saying that's what caused his scratches. Haha.

Brass scratching/gouged are my biggest concern cause I reload. A sharp extension not only scratches the bullet, it gouges the brass neck and shoulder pretty bad.

The part of his bullet that is scratched looks to be above the ogive where the rifling will contact the bullet. Probably wouldnt see any negative effects unless your shooting for precision at long distances.
 
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hlee

Sergeant
Jul 14, 2012
1,144
273
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TX
#16
Fig's point is that when the rifle is fired, the rifling mars the bullet jacket to a greater extent than the feed ramps. How does the gun shoot? If the precision is up to expectations, shoot it. Just another case of "if it ain't broke, fix it until it is..."
 
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