I just recently bought my first ar15 (stag model 2) and i have an issue.
i went through 50-60 rounds of Winchester 55 gr without any issues ,but then i started using American eagle 55 gr and within 30 rounds I've had 1 round the brass primer ended up in my magazine and two rounds the primer ended up staying in the chamber just under the bore hole stopping the bolt from closing all the way on next round.
as i said before this is my first time ever using an ar15 ,but i have had many different guns throughout the years and never had this problem with any of them.

is it the ammo ?
is it the gun ?
 
Thanks

Clean out the chamber, sounds like there is some gunk in there causing some over pressure.

it does have some clp in there that's set for about 2-3 weeks but i figured from what i had been reading that it was ok as long as i ran a snake through it before i shot it again.
i cant really find a straight answer as to how wet the ar should be inside. all my previous guns were under 500 so i kind of barely ever cleaned or lubed them but this gun set me back a bit so i want to baby it.
I will take your advice and clean it well tomorrow and try it again.
for not shooting a gun for several years i was nailing 1-2 inch rocks at about 25-30 yards standing not sure how good that is but it felt good anyway.

thanks for the advice azoutdoorsman

Especially when new and during the break in you have to keep it clean and lubed.  American Eagle is not bad ammo so...
 

i live right on the lake so humidity is a prob for me also and as for high temps we had quit a few 100 degree days here since i cleaned it last plus i keep my guns in a non air conditioned room.
i appreciate the advice guys and i will clean it before i shoot it every time now its much easier then digging out all the brass pieces.

Thanks again you guys

I had the same exact thing happen recently and I was using Independence XM193 5.56. First thought that crossed my mind was that it was an out of spec chamber because the first issue was popped primers about every other round. This isn't a full factory rifle and it was just purchased as an upper.

It got better after shooting 20 and the popped primers stopped but, I then had a few double feeds. I brought a back up rifle and it ran the same ammo 100% out of 60 rounds so, I figured it was the rifle. When I first got it (mid August), all I did was lube the bolt and run a boresnake through the barrel then, let it sit for a few weeks. Before I was going to contact the manufacturer, I figured I'd give it a real good cleaning. Proceeded to degrease the chamber, scrubbed it with a chamber brush and mop, then ran some patches to clean out anything that was left behind. Lubed it with some Fireclean and headed to the range.

I was able to fire (70) trouble free rounds today but, I didn't test the original ammo I used initially so, maybe try giving it a good cleaning and have another go at it?

For over 36 years, I have been cleaning M16s/AR15s. I started out with just using LSA. SOme of you guys can remember this stuff. I always make sure my bore and chamber are clean and dry. When it is dirty, I run a brush through the bore one time to loosen any residue. I then use some CLP on a patch and run a couple like this through the bore. Then, I shoot a little bit of gun scrubber into the barrel to give it a good rinse. I then run a clean patch through it until it comes out clean. Once I have cleaned the BCG and upper receiver, I will apply liberal lubrication to the BCG. I have done it this way and never had one issue. To me, a clean bore is a happy bore.

I live in Georgia where it's hot as hell and humid 7-8 months out of the year. I run my AR's wetter than a prom night vagina; I shoot American Eagle 5.56, Federal (Lake City), Independence, basically the same ammo as you OP and have never had a problem with popped primers. But with the other accounts of the issue I'm believing a wet chamber can cause over pressure and I'll dry all my chambers today. Not bone dry but definitely dryer than previously.

Jesus this place has really turned into the blind leading the blind.

It's not a dirty/oiled bore/chamber that's going to cause popped primers. It's over pressure and/or gun unlocking early coupled with ammo that has either loose primer pockets and/or un-staked primers.  It's a combination of those things. A heavier buffer might fix the issue, avoiding FC headstamp federal brass might be prudent as well.  Stag/CMT makes a good gun so I'd edge it toward the ammo.

I guess a REALLY dirty gun could in theory cause an overpressure if the throat was really gnarly but if the cartridge chambers the chamber isn't to blame. OP stated he's put less then a hundred rounds through the thing, so yeah, no.

Wet chambers don't cause overpressure. Heavily oiled bores yes, chambers no.

Wet chambers cause increased bolt head thrust. The case as it expands during firing instead of gripping the chamber walls it slides backwards and more force is applied to the bolt. You'll break lugs off the bolt head.

Run it like a wet puss!!

Could be ammo was loaded too hot.

I run my bores oiled too but forgot to specifically mention that. I'm stopping that practice today. It's never been a problem before for me, ever. I'm glad I ran across this thread.

Unless you oil after every shot, you're only doing it once. That oil is long gone after the first shot. It's not going to cause reoccurring pressure issues.

+1

Sometimes there's gunk from the factory that can cause over pressure. Dried lubricant, or preservative, machining debris, oxidation. I know this from experience.

 

No

If a cartridge feeds and the bolt closes then the chamber alone won't cause over pressure.

6-7k worth of 22 will leave a good ring of carbon/lead in the throat/leade are. That's going to cause overpressure.

It might be semantics, but I think of the throat/leade and the chamber as two separate and distinct parts of a barrel.

Benchrest shooters that only neck size have cases that are tight in the chamber. Just as tight as if you had carbon build up in the chamber. They use the bolt camming down to get essentially min headspace. No over pressure.

Now, load coal long and jam the bullet into the lands or have a ring of lead build up from a 22lr adapter and suprise! Overpressure signs.

It wasn't 6-7k of 22lr consecutively. It was mixed with 223/556, which vaporizes some of the build up during firing.

I don't mean for this to be a pissing contest. I'm just trying to help.

If the build up is in the chamber body yes, I'll dispute. Funk in the leade/throat? On yeah.

I'll give you the neck, as enough shit there could cause issues.

In the end OP had only shot 90 rounds. It's far more common to have extraction issues with a dirty chamber and he's not showing signs of that. I'd bet its the ae223.

Same here, I'm sharing personal experiences and I also like to learn from others.

 

Clean the gun thoroughly. Shoot Federal 5.56 xm193. If the gun still acts funny, its the gun. I suspect the ammo.