Deep Scratches on Sides of Cases - DPMS AR

H

Huck1969

New member
I just built an upper in 7mm-08 for my DPMS lower. I bought a barrel and barrel extension from a barrel manufacturer and had them torque them together and drill the gas port. The remaining upper parts I purchases from DPMS. After putting it all together and checking headspace I took it to the range and fired seven rounds- 2 factory loads and 5 reloads.
I am getting deep scratches along the side of the case and case neck. Following initial firing, and at home I have done extensive tests with dummy loads (no powder) by cycling them from the mag and then ejecting. I am indexing the case to the 12:00 position (marked with a Sharpie pen) in the magazine. I get the same scratches _ along the length of the case where I marked it, and extending along the side of the bullet. I have several AR15's and an M1A and have reloaded thousands of rounds for all of them and Never seen scratches like this. They are deep enough to feel with a finger nail.
I have made numerous phone calls to the barrel manufacturer and techs at Brownell's, and even looked at the teeth on the barrel extension with a borescope but not seen obvious burrs. I have gotten advice to try polishing the teeth of the barrel extension with JB or other rubbing compound using a soft tip of a Dremel tool. I've done that and still get a scratch in the same place along the case and bullet (12:00 position of the case as it feeds).
I am frustrated and about to go to a gunsmith. Can any of you experienced AR shooters offer some advice?
 
Some things to check:
Is there a sharp edge on the mouth of the chamber? If so, polish the chamber and lightly chamfer the mouth of the chamber
Is the magazine gouging the shell? If so, lightly stone the lips of the magazine with a very smooth stone.
Is there a burr internally at the neck area? If so, polish the chamber, and while you're at it, chamfer the mouth of the chamber.
 
Thank you for your reply.
I have checked for burrs forward of the barrel extension and inside the bore toward the leade, both visually and with a borescope, and their are none.
As for the magazine lips, the gouge on the case is at the 12:00 position as the round feeds and ejects; the mag being at the 6:00. I just tried using some steel wool, just on the "teeth" of the barrel extension where the bolt lugs lock. After wiping clean I still get the prominent scratch down the entire side of the case.
 
Do you insert a loaded magazine and then retract the bolt to chamber a round? If so, check the bottom of the bolt or carrier for a burr or sharp edge that could be scoring the top round as the bolt comes back.

Jim
 
For Jim K
I already have the bolt back when I insert the mag with one round in it. I mark (index) the case with a Sharpie pen at the 12:00 position then insert the mag and activate the bolt release. I then pull back on the charging handle and eject the round. With this procedure the bolt lugs never touch the sides of the case.
Thanks for the reply. Any other ideas?

Jim H
 
Does it look like this in the photo? Sorry about the blurry photo,it's not easy to focus on.

Wow I thought I was the only person thats ever experienced this. I have experienced a gouging issue in the past with my AR. It is a deep gouge and can feel it with your fingernail. it would start at the tip and go down about half way down the case in a slight spiral. Mine was deep enough it would stop the bullet during loading in it's tracks. I couldn't see or feel anything on the feeding ramps. It would jam repeatedly when tryin to shoot or cycle manually. I ask for advise on several forums with no other members ever running into a issue like this,till now. Maybe it just needed to be broken in but i'm not sure.

My AR was inherited with little info on the rifle. The upper is unknown with a A by the rear sight which is Anchor-Harvey forging company. The caliber and barrel manufacturer is unknown,no markings on the barrel. It did have a heavy barrel with a mil-spec bolt. The barrel is believed to be a Olympic or DPMS. So I just shoot 223 out of it since i'm not sure if it is chrome-lined or not.

No one was ever able to give me any advice on how to fix the issue. I got several suggestions to polish the feed ramps as well,it didn't work in my case. I tried it with no improvement at all. Finally I got fed up and I figured it's screwed up already so I had a idea. I'm no smith or anything this was just my way of doing it.

I used a needle file about gently two to three strokes per side of the edge of the feed ramp. Then I used 400 grade utility cloth wrapped around a flat head screw driver a few times to go a little smoother. Then I followed that with polishing compound using a dremel tool. I did this whole process about twice. I tried it once and was big improvement but not 100% resolved so I repeated it again. After the second time doing this it was perfect. It may sound crazy but it worked for me with great success. It does not leave any scratches or gouges and feeds great now. Or you could take it to a smith.

Hope this helps at least get you pointed in a direction. Good luck.

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Thank you, and the scratches in those photos look just like mine. I was about to do what you decided to do with a file. Since you "filed" the feed ramps it sounds like you were able to mark a case, put it in the mag with the mark on the case in a certain position and thus determine that the scratch is (at the 6:00 position) from the area of the feed ramps. As you know my scratching is occurring at the 12:00 position so I am polishing those teeth. I will look into buying a very fine file to fix it.
Thank you

Jim H.
 
Their a several piece set and only $10.00 at home depot. Well worth the investment. Just be easy and don't over do it. Just try and test a little at a time. If thats the route you decide to go. It might even wear itself in after a while. Mine wouldn't feed enough to really even shoot it. It was just too frustrating.

My gouges seemed to happen more toward the point in the center were the
/\ is located were the squared edge is. It was a little worse on one side compared to the other.

These are the ones I used. I just left the handle off to make it easier. Their may be something finer than these out there but it worked.http://www.homedepot.com/h_d1/N-5yc...splay?langId=-1&storeId=10051&catalogId=10053
 
Thanks 7J7-
I'm off to Home Depot today to buy a set of them as they would be handy to have anyway, whether I use them or not on this rifle. It is frustrating that there is no visual evidence of burrs, yet somehow these deep scratches are occurring, just as in your photos. Since the gun fires fine, I could hope that this will change after firing several hundred rounds but that's too many cases badly scratched, for a reloader to accept. Also I would not expect the soft brass of a case to do much to file off a steel burr in the chambering and ejecting process.

Jim
 
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