AR 10 DPMS feeding issues

[Citified]

Gregg:
I was in the first thread trying to help you. You are getting advice that is all over the board here. I'm sure the intentions are good.
The information item I see missing from the other thread is your statement the bolt carrier group sometimes does not come all the way back and misses the base of the second cartridge which hits the center of the case causing a jam and dent.
Is this still the situation?
If it is, the bolt will not strip the round from the mag and chamber it.
I do agree with the detailed information Cohunt provided. The cartridges should have a slight nose up position in the magazine. This is easy to accomplish and then we can move on to other diagnostics.

 

[jimb100]

Lubricant should help. Also some need to have a little break in time. Also I have found if the have a coating on the upper receiver sometimes it will jamb.

 

[VNPathfinder]

Never heard of a shim that raises the barrel In relation to the lower receiver-- can you provide a link?

The shim doesn't raise he barrel. It extends the barrel slightly away from the lower thus decreasing the angle of the feed ramp relative to the magazine. The shim kit comes with 4 0r 5 shims of different thicknesses that look like washers and they slip over the chamber end of the barrel. this increases the distance between the mag and the feed ramp. I just looked on Midway and couldn't find them but a friend is checking and will let me know where he got his.

 

[grandedirt]

There is an inherent issue with a lot of the 80% LR308 type lowers. I believe it has to do with how the mags are held in the lower. I think they are held too low. I saw the exact thing on a friends build. It would double feed constantly. He tried an adjustable gas block, buffer and spring.
Even tried 3 different types of mags.
Nothing worked.
He finally changed the power to an Aero Precision 308 lower.
The gun runs flawlessly.
It was the lower

 

[Gregg C]

Gregg:
I was in the first thread trying to help you. You are getting advice that is all over the board here. I'm sure the intentions are good.
The information item I see missing from the other thread is your statement the bolt carrier group sometimes does not come all the way back and misses the base of the second cartridge which hits the center of the case causing a jam and dent.
Is this still the situation?
If it is, the bolt will not strip the round from the mag and chamber it.
I do agree with the detailed information Cohunt provided. The cartridges should have a slight nose up position in the magazine. This is easy to accomplish and then we can move on to other diagnostics.

Citified, I'm not certain that the bolt isn't coming all the way back. I was thinking that the case head was being forced back down in the mag because of the, in my mind, really steep ramp, allowing the bolt to slam forward against the side of the case. After looking at my mag, a C-Products, and other mags posted here, I am fairly certain tipping the nose up is going to help. I spent some time last nite bending the front of the lips up, and deburring them, and am hopeful that my issue is solved. I will find out on the weekend, and post back, one way or the other.

 

[ARlife4me]

There is an inherent issue with a lot of the 80% LR308 type lowers. I believe it has to do with how the mags are held in the lower. I think they are held too low. I saw the exact thing on a friends build. It would double feed constantly. He tried an adjustable gas block, buffer and spring.
Even tried 3 different types of mags.
Nothing worked.
He finally changed the power to an Aero Precision 308 lower.
The gun runs flawlessly.
It was the lower

I agree with this and will add to it. I've had mags sit just low enough also causing feeding issues of the same nature. The crazy issue was the mag release. Not saying that is this issue, just 1 I had. 10's are more temperamental than 15's are on every aspect! Try different ammo before doing anything else. Get something that is FMJ, no poly tip or soft points. The ammo you have seems to be or have erratic pressure changes.

 

[Citified]

 

[Vasily]

95% of ar malfunctions are magazine related. Can cause anything from feeding issues to false high pressure. Any AR10 platform not built by a genius is likely to have issues. The mag however, is likely the culprit. I'm not a fan of Magpul....gen 1, gen 2, gen 3. How many gens does it take to make something that's reliable. However, my gen 3 p-mag has been the best I've tried. Tweaking feed lips is a viable option but if the bolt catch isn't working your outta luck with that mag. Be very, very careful with slam fires. They happen often when releasing the bolt on a live round....keep a nice new retainer pin the Bolt Carrier for the firing pin and never test feeding with a live round...use a dummy. Load a dummy in the mag and slowly release the bolt watching how it's picking it up out of the mag. Use a flashlight to help see. Do this several times to see what's going on. Tweaking AR10 comes down to minute changes and persistence. Just remember 95% of the time it's magazine related.

 

[Lefty G-gear]

This is what the rifle is doing...View attachment 361355

Why all of that oil in the AR? Make the chamber and receiver dry!
And use these mags n chuck the aluminum ones!
Easier to load, easier on your fingers! And they feed more reliably!
They make 5, 10 and 20-rd. mags. SEARCH.

Magpul PMAG GEN M3 LR/SR-25 .308 / 7.62x51 AR-10 10-Round Magazine

This is a Magpul PMAG Gen M3 10-round magazine for AR-10 rifles chambered in 7.62x51mm / .308 Win. Crafted from durable, improved polymer with stainless steel internal springs, t

gunmagwarehouse.com

AND the buffer may be too light! - Get a heavy 5-ounce, or so!

AR-STONER Heavy Buffer LR-308 Carbine SS

AR-STONER offers replacement components for the LR-308. These high quality components provide excellent fit and reliable function. AR-STONER parts are...

www.midwayusa.com

SOLVED!

 

[436]

This is what the rifle is doing...View attachment 361355

I don't believe you said whether you did, and I didn't read all the other posts, just have a couple of questions;
Can you hand-charge the weapon from a full magazine?
Can you hand-charge the weapon with only one round in the magazine?
Can you chamber a cartridge and fire it with a full magazine and have it chamber the next round?
Can you chamber a cartridge and fire it with only one round in the magazine and have it chamber the next round?

Never bend or take off any metal until you are pretty sure you understand the problem.
Cheers

 

[Armalite7.62]

This is what the rifle is doing...View attachment 361355

MAKE SURE your bolt is well LUBRICATED but make sure you don't lube your chamber. I have had that happen with my AR-10T and voila, a syringe of oil lubing the bolt solved it. Be very careful, I have seen guys shoot oil into the chamber and they risked over pressurization which could blow the magazine right through a guys wrist. IF you have an adjustable gas block that needs to be tuned is a possibility. Call Glen at Armalite in the Tech Department and tell him what is going on. He will be glad to listen.

 

[Pro2A]

Howdy, all. I finally bit the Bullitt, and got myself an AR. It's an 80%, built by a friend of mine. Near as I can tell, he did a good job. Let's assume he knows what he is doing.
The issue is, it jams. I know NOTHING about gas guns, so I want to tinker with this thing, fix the problem, and in the process, learn something.
On another thread, lots of GOOD information was given. Not my thread, so here we go...
So far, I have polished the feed ramp. Seemed to help some, but I did not document failures previously, so I don't really know. What I DID learn was it's from the right hand column in the magazine that these "jams" occur. Some of the guys in that thread suggested adjusting the mag lips up a touch to allow the cartridge to stick up into the bolt path more. Having decided to try that next, I noticed the back end of my mag wraps around the case head. Seems to me that if I just bend the lips up, only the shoulder will come up, and I want the entire shell to come up. Am I right? So that means I need to cut the back of the mag , to free up the whole feed lip. Am I all funkered up here ?View attachment 361354

Well, you sure started out the harder way to learn about ARs. The AR10 versus the AR15 platform, home spun input in parts selection, machining, assembly........sink or swim throw the kid in the creek, see if he's SEAL material, or NOT...... Even before we had driver's licenses, cousin and I were given an old car with "transmission trouble." First step....remove tranny on neighbor's drive (yeah, I don't either....) second step.....???above our pay grade.....beat the Hell out of us????. Uncle came home, first question, did we run it, confirm issue, troubleshoot it? UH, that wasn't on our project plan!!! My first engine for one of my early Vettes....'62, I let a "friend" machine/thread the rocker studs because his dad had a vertical mill......we jimmied the lock on the shop.......first mistake.....many followed. NOW YOU TELL ME, the studs are NOT to look like a Hemi porcupine. Spent more fixing his expertise than I could have bought new hipo heads for. It has been a L-O-N-G road from that tranny through Engineering BS/MS degrees, 50 years of business/product/wealth building, learning to learn first when possible. Welcome to ARs....JUMP RIGHT IN!!! They are addictive, the Legos/Lincoln Logs/Tinker Toys of guns.....but, not necessarily fully interchangeable between platforms, brands, designs. You "assumed" .....ever hear what assume says when broken apart......your home boy knew what he is doing, and still, here you are.....tranny removed. Just funning with you. Been there, done that, learned this. It's more fun on this side of the "O****" learning curve. Opportunity presents itself to you on a platter...er, AR10. I paid my dues in spades, and trannys.....NEXT!!! (Never saw myself becoming a grouching old ***, but here I am.....KILLING IT!!!!) You state you know nothing about gas guns. First step in the right direction.....point proven.....too late. But, what do you know? Are you technical, a troubleshooter, a fixer, or NOT....a tranny yanker??? Both Brownells and MidwayUSA have great free AR learning videos on their sites. Also, American Gunsmithing Institute (AGI) has great AR gunsmith, function, assemble, dis-assemble troubleshooting videos for ARs and most other firearms. Maybe a friend, or forum member, might have the AGI video you could borrow. (I've got them all, but no longer waste heartbeats chasing loaned stuff with unknowns. Not sorry.) Check YouTube for surprisingly helpful videos. Often videos are more helpful than typed forum responses. Old boss, VP at Mary Kay, used to say, "Assume competence, but follow up like Hell." How many proper functioning AR10....or even AR15..... assemblies has your home boy completed previously?? Is he the retired SEAL Armorer,....doubtful or you wouldn't be here.......... or living-in-mommy's-basement guy? Are you the FNguinea pig? Did he select the parts? Assemble everything? Machine the 80% receiver on a mill or a drill-n-jig rig??? Your home spun input is another variable. IE....don't assume anything. Be aware that long action 308 platform AR is not "Mil-Spec" as the 5.56 platform is/can be/isn't necessarily. All AR10 manufacturers fabricate to their own prints, designs....some not interchangeable, compatible. Are all the assembly parts from same manufacturer, a complete one supplier kit, or a hodge-podge of mix-'n'-match good deals. Mix-'n'-match on bigger platform can induce function problems more so than 5.56 platform. Might "mix-'n'-match" upper and lower assemblies and mags with known proper functioning like assemblies to see if you can isolate the area of the issue. Magazine issue, upper issue, lower machining issue..... Compare your design....gas system length/parts/assembly, bolt carrier assembly, return spring/buffer assembly,........to known functioning gun systems. Confirm mag feeding in other functioning full assembled gun. Confirm upper function with known good mag and known functioning lower. ARs like to be run wet, especially new. You can machinist blue a cartridge in area being damaged and with another orientation mark to specifically confirm where the mark originates. Check those areas for minute burrs that might cause drag. The AR world is your oyster. Good luck. Keep everyone updated. Happy tranny pulling.....

 

[Pro2A]

. Call Glen at Armalite in the Tech Department and tell him what is going on. He will be glad to listen.

". Call Glen at Armalite in the Tech Department and tell him what is going on. He will be glad to listen."

When I talk to myself, one talks, one or several listen.....and then, we laugh and laugh and laugh and laugh..........one just mumbles. Just an really old guy and his friends sharing.......you will get there, hopefully. (Although at Easter I buried a really dear fantastic 36 year old lady friend......cancer.....laughs on hold, believing in their return someday.) She truly enjoyed when my friends and I laughed and laughed and laughed....she joined in. It was a fun place.........to be again.

 

[Jonn264]

This is what the rifle is doing...View attachment 361355

This is what the rifle is doing...View attachment 361355

Gregg, I have a DPMS AR-10 SASS. I had a similar issue when it was right out of the box. My problem was that it was hard to feed a round into the chamber manually or after firing. The problem was that the buffer didn't go back far enough to get behind the bullet in the magazine. Look on the end of your buffer for a circle dented into it by the screw holding the top of your stock onto the end of your buffer tube. The circle is caused by that screw being too long and every time you fire the gun it strikes the screw. I fixed mine while on the range by putting a washer on the screw. I always said I'd take it out and shorten the screw, but I never did. Don't fix what works. I've included a picture of the buffer with the mark on it.