Hello all,

I just got my AR-10, and I am having a feeding issue.  I am using brand new P-Mag 20 rounders.  The rifle is very lubed and clean.  I used two separate bolts one standard (Radical Firearms) and one complete nickel boron bolt (DPMS).  When I put a loaded magazine in and slammed the bolt home, only about 10% of the time does the round load properly.  When loaded the round fires, it fires beautifully, however, it does not load the second round.  The bolt closes on top of the next round about 3/4 of the way to the end of the casing.  Other times the round goes up in the air and does not chamber the round.  This malfunction occurs if I am shooting or if I am cycling round manually and pulling the charging handle all the way to the rear myself.  It does not seem like a gas issue, to me because I can cause it to happen manually too, I am thinking maybe it upper is too high from the magazine?  This is 80% build, and I have built six 5.56 rifles without any problems, this is my first .308 rifle.  I dont have any pics or it, but I am sure I can take some.  It does eject the spent casing flawlessly.  The ammo I am using Colt .308 factory.  I am very familiar with the AR platform, and have carried a Bushmaster for a number of years.  

Really frustrated.
Steve

a bit difficult to understand the problem here, when you say the bolt closes on top of the next round about 3/4 of the way... this is a symptom of the bolt not going back far enough to engage the rim of the next cartridge. the next part is really hard to understand...does the next cartridge get tossed out of the rifle somehow?

Are you mixing a DPMS type bolt and carrier with an Armalite type barrel, or receiver extension?

had this too and know what OP is talking about. Bolt carrier is not going back all the way. Last round is extracted, bolt goes back over next round but NOT far enough back to pick it up. Bolt winds up 3/4 the way over magazine.

I assume BCG is proper type, lubed, and installed correctly.

Next thing to check would be the gas system. Is the gas tube correctly installed in gas block and is gas block aligned correctly with gas port?

Some of the .308 barrels come with an undersized gas port. You may have to open it up. There is a reference chart somewhere, I seem to recall that I had to open mine up to .093", and it was quite smaller than that originally (DPMS)

Similar problem I'm having, except worse than mine.
This is not gas or bolt not going back far enough, since it can be replicated by pulling and releasing the CH.
Maybe not enough forward momentum from the buffer spring or interference somewhere is what I'm thinking.

Sorry I wasnt clear the first time.

I have a DPMS style .308 AR.  

I dont believe the problem is the gas system, because I can replicate the problem without firing, by pulling the charging handle back all the way to the rear and allowing the bolt to slam home.  For lube, I use frog lube, and the bcg is dripping almost.  It almost seems like the upper receiver sits up too high for the bcg to catch the next round in the magazine.  The loaded round fires and ejects with no problems.

 
This is a photo of one of the malfunctions.



This is the second type of malfunction.



This is what some of the rounds look like.

Here is pics of the bolt touching the next round, to me, it does not look like the bolt is catching enough of the round?  Not sure though.




I have used brand new P-mag 20 rounders and brand new DPMS 10 rounders, same thing no matter what mags I use or how many rounds in the mag.  

I think you have correctly identified the problem, which is that the magazine is not at the correct height for the bolt to strip them off. first, make sure the screw for the mag catch is flush with the release button. is there much vertical free play in the magazine when it is locked in by the magazine catch?

Are you using a .223 or 308 buffer in your receiver extension?

As far as play in the magazine, not much at all, less than other AR's I have.

Everything on this is .308 nothing used is .223.

Ok, if there is too much separation between the bolt and magazine, what can I do to fix it?  Do I file down the top portion of the lower that meets the upper?  Is there something I can to raise the magazine level?

don't alter or file on the upper or the lower. put a few rounds in the magazine, put the magazine in the rifle and then rest it on top of something to force the magazine as high as possible in the magwell. does the bolt strip rounds off the magazine or not?

Yes once in a while the round will be taken out of the magazine and loaded correctly, but maybe 10%.  Yes the bolt will lock back one an empty magazine.

I will try loading with the magazine pushed up as high as possible and see what happens next.

I google imaged AR 10 magazine release and took a look at what was out there and some of the aftermarket competition units had been beveled to the point of barely holding the magazine in place. take yours out and take a look at it.

It appears that the magazine sits too low in the lower receiver. One photo shows two rounds in the magazine and it  looks like they are stacking sideways on each other, round #2 is binding sideways in that magazine. Are you running the original followers? There shouldn't be enough room in the mag for this to happen. Spring tension should force them to fit the follower inside the case body.

There is no way for your bolt to strip a round when it has so little purchase on the case head. It looks like less than 1/16" of the bolt is actually pushing the round from the magazine. This needs to be doubled or more. Contact the manufacturer of the lower, perhaps the had a run of out of spec lowers.

You can make a magazine fit lower in the upper, not the other way around that I'm aware of.