AR 10 DPMS feeding issues

[VNPathfinder]

I've built several AR10's and had similar problems . They were caused by the barrel being too close to the lower receiver but were easily fixed by installing shims between the barren and the lower. A shims kit is available at Midway for minimal bucks. AR 10's aren't built to milspecs since none exist. Hence slight differences in dimensions from different manufacturers.

Good luck

 

[jasonprox700]

I didn't see what mags you're running, but I'm going to assume the standard DPMS?

My first 308 rifle had feed issues (factory Gen 1 DPMS AP4). I tried polishing the feed ramps, swapped out the gas block for an SLR adjustable, and played with buffers. Nothing. Gun would still have feed issues no matter what I did. I was pretty green so I had no clue it could be a mag issue.

I ordered a couple Magpul mags since I had such good luck with them in 556. I can honestly say that while running the Pmags, that gun ran 100%.

Might be worth a try picking up Magpul Pmag.

 

[Travis H]

Not to be this guy but you might want to delete first paragraph of your comment. Building your own gun is legal without serial number. However buying an 80% someone else made gets you both in trouble. Unless its serialized, but ur comment did not say so...

 

[Kendoist4162]

THIS

 

[Crusty Buck]

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

I have owned two gas guns, RR Arms in 223 and Aero in 6.5 Grendel. Never had feed problems with the Rock River. I fought with the Grendel plenty. It never James, but failed to shut the bolt, or eject. A different buffer spring and gas block adjustment solved that. Also, new mags have very heavy spring tension. Sometimes rounds won't strip smoothly. If you cut the tangs off, you won't be able to seat your top two in the mag. Also recheck your COAL.

 

[Knifeguy]

A lot of good info here. Let me start by saying you can try 742 different magazines and if the issue is caused by something else you are simply chasing shadows. First looking at the marks on your cases I would ensure the rifle is not short stroking. Place a single round in the mag, load and fire. If the bolt strips the round and chambers it and If the bolt locks back with the mag empty it is not a gas issue so you can move to the next system. If it operated properly and locked back on an empty magazine it is most likely not a Spring or buffer issue either. If it functions properly with one round it should in theory function properly throughout a full magazine. I am going to share with you my opinion here. There is a very valid reason tens of thousands of military issue magazines are sold off as surplus every year. It is far easier to tweak the lips of the magazine than most people realize. Cohunt shared a ream of info on magazines and for good reason. Magazine issues are the single largest feeding issue in AR platforms. Just slamming the mag against the side of the mag well can cause problems. I have never, one single time witnessed a Magpul Polymer mag fail to feed in a properly running rifle. I do not own stock in Magpul nor am I attempting to sell anything. I am sharing my personal experience. In the Sheriff's Department I retired from they did away with all factory magazines and went to Polymer. The failure to feed issues all but ceased. Try these things and please let us know what you find. Best of luck to you !

 

[cohunt]

Not to be this guy but you might want to delete first paragraph of your comment. Building your own gun is legal without serial number. However buying an 80% someone else made gets you both in trouble. Unless its serialized, but ur comment did not say so...

Gray area-- federal law says you can build your own firearm for personal use, just not for sales or distribution purposes - it doesn't say after "personal use" you can't sell it or gift it without serial numbers-- nor does it specify for how long you must jave it for "personal use" before you could sell or gift it--- many states still have legal face to face sales too.

Also op didn't say if he did the machining of the lower under the guidance of his friend.

Lots of left out info and all of it clouds what this post is really about-- trying to help the OP troubleshoot his problems.

People will argue this for days, I'm not sure it's ever been legally challenged so its up to the individual to "interpret" the law and be responsible for any consequences.

Hopefully the OP's thread won't turn into a "ghost gun" argument

 

[bbroyhill]

I know on mine it was a magazine issue.

 

[cohunt]

I've built several AR10's and had similar problems . They were caused by the barrel being too close to the lower receiver but were easily fixed by installing shims between the barren and the lower. A shims kit is available at Midway for minimal bucks. AR 10's aren't built to milspecs since none exist. Hence slight differences in dimensions from different manufacturers.

Good luck

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

 

[BPollard]

It's either of the gas block and or buffer weight

 

[Stonyman88]

Need lots more info of where and how the cartridge is jamming in the barrel or never gets to the barrel, Is the shell jammed right by the throat, not into the chamber? like most of the shell is still in the mag.
? Please explain where the round jams? One issue is the front of the mag. if it's flat across the front just ahead of the bullet nose, the round can catch on the lip of the case, which holds the round for a split second and causes the round to enter sideways, or on a 25-30 degree angel , take a grinder, dremel tool and make a half moon in the front of the mag. this keeps the round from catching the front of the mag. Not sure how your round is jamming , that would help to know, from what you explained is it never gets into the chamber, correct? From the looks of your mag. it's flat in the front, and need to have a 1/2 moon shape, ,What happens is the bolt hits the round and starts it forward, since they is no support in the front of the mag holding the shell the front kicks up, but if it starts forward and catches the lip of the front of the mag, it stops for a instance and will jam. Let me know what you find out. I had this issue on a 450 Bushmaster, rounded the front of the mag and wala , works perfect now. Cohunt also has a good idea, but make sure you head space is OK if you shim it.

 

[Tex_Hunter]

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

9 times out of 10 with a large pattern gas gun it's going to be that it's over gassed, assuming the gun is otherwise quality parts/properly assembled.

Your brass being all chewed up is a pretty good indicator of that as well. An AR15 will run with too much gas unless it is just really bad but the 308 guns are noteiously finicky. Heck my $2000+ LaRue AR10 had an almost identical issues as yours, it was unusable with a suppressor and would still double feed every 2-3shots without the can on. I'm normally not for just throwing parts at the problem, but just buy an Odín Works adjustable gas block and that will likely fix you problems.

 

[Vipervi]

On one I built and was having similar issues. tried everything gas & spring related. I did a slow mo recording into the ejection port with just one round loaded. It was dropping the casing on the way out. put a stronger ejector spring & o-ring on the ejector and problem fixed.
Just my two cents worth.

 

[Mmac52280]

Just my two cents, but I have more than a few AR's in multiple calibers. EVERY feed issue was magazine related. One method that helped works better with two people. Maybe a mirror can help. With a loaded mag in the gun, work the bolt by hand. If the bolt has to slam the round to get it to feed, it needs tweaking. Observing the cartridge movement in slow motion should identify the issue. We have noticed cartridges tip up and down as they move forward. Some only feed well with 10 rounds, but jamb when full. Cheap mags are often a problem. None of my AR-10's like the plastic mags, only steel, and every one needed tweaked. Aftermarket mags are built to really general specs, never to something you assembled.