NOT Grendel but need some input. Re: popped primers.

[1075 tech]

My first AR build was a 5.56. 16" SOCOM profile nitrided barrel, 1/7, Carbine length gas. Upper was allegedly built/assembled by JSE but not bought from them.

I was using ZQI 62gr ammo. The first couple times shooting this rifle, I was getting ejector swipes on the brass as well as a few primers coming completely out of the pocket. Being an AR newbie, I initially wrote this off to a: break-in, or b: poor quality ammo.

Eventually, these problems resolved and further shooting had no problems.

Yesterday, these problems resurfaced. Primers coming out of pocket on ZQI ammo, WITHOUT ejector marks and also shot some Independence 5.56 55gr (FC brass). These exhibited some of the same signs as the original ZQI. Popped primers and heavy ejector swipes.

I had no pierced primers and this did not happen with every round.

Other than over pressure caused by chamber/barrel/bolt issues, can these symptoms be caused by over gassing? Thinking of replacing the standard buffer with a heavy buffer. Thinking bolt unlocking early?

Still learning.

BTW, my Grendel build functions well. Only a few cycling issues with Wolf Gold 120 MPT.

[VASCAR2]

The Independence ammo had some lots which were very hot and I have read where QC with ZQI was questionable with some lots of 7.62X51. I haven't read any reports of ZQI 5.56 popping primers but that doesn't mean you didn't get a bad lot. If I were in your shoes I'd buy some Federal American Eagle 5.56, Winchester White box 5.56, IMI 5.56 or Wolf Gold. If the ammo functions with any of those loads and does not pop or pierce primers I'd say your luck ran out and you got two bad batches of ammo. If the ammo I suggested did pop or pierce primers I'd check the chamber with chamber gauges and check the bolt to see if either is out of spec.

Another thing to consider is the ambient temperature when your shooting. When my PD started issueing rifles and doing training or quallification shoots we had a few primers pop with LC M-193. In every case I witnessed the temperature was in the 90+ range. On cooler days never saw a problem. Temperature can have an effect on some powders, some worse than others. Had you been shooting ZQI last summer, saw problems then nothing in fall and winter but now as temperatures rise you start getting the same issue. Something is on the edge of tolerances, ammo or rifle. Hopefully it is an ammo issue, you might consider shooting the ZQI and Independence in another 223/5.56 AR-15 and see if it pops primers.

[1075 tech]

Now that you mention the temperature thing, that may be something. I don't recall what it was the first couple times out. Last time out it was cooler Yesterday was 85 and we were in full sun.

I also noted that the ZQI was ejecting at 330 while the Independence was ejecting at about 130 - 200.
ZQI maybe 1 primer out of 20. Independence blew 4/10.

I had shot some AR-223 (Federal?) w/o issue other than horrible accuracy.

[CPT.CRAZY]

My first question, is the barrel marked 223 rem. or 5.56? I had similar problems using 5.56 ammo in a 223 barrel. The 223 marked loading should be a little lighter load.

[1075 tech]

My first question, is the barrel marked 223 rem. or 5.56? I had similar problems using 5.56 ammo in a 223 barrel. The 223 marked loading should be a little lighter load.

Barrel is marked 5.56.

[borderpatrol]

Popping primers and ejector marks means you have a serious problem. I would stop shooting the upper and contact the barrel manufacturer.

How many rounds through this upper?

You bought it new or used?

Save your fired brass and send it with the upper. They can measure headspace of the fired cases (so can you with Hornady's Lock-N-Load headspace gage kit) and inspect them. They will check chamber headspace using the appropriate gages.

You may have excessive headspace. This is very rare on new firearms.

Some rifles get a build up of carbon and copper in the throat area which can cause pressure spikes. Thoroughly clean the barrel using a copper remover or Kroil/JB Bore cleaner until it's spotless.

Try some standard .223 ammo after you clean the barrel. You may have a .223 chamber and the barrel is marked improperly. Getting two batches of "bad ammo" from separate manufacturers seems almost impossible. The odds are very high that this isn't the problem.

Allowing your ammo to sit in the sun will cause over pressure issues on a hot day.