AR 10 POPPING FACTORY AMMO PRIMERS

[woodnut]

Recently, I had an AR10 rechambered by a fine smith from 6x47Lapua to 6 Creedmoor. Went to test and zero it and two factory rounds had their primers blown out. Inspecting the primers showed no other pressure sign, but was black round it and the pocket was all black. Only two out of maybe 6 rounds. Other fired cases showed no pressure signs. Rifle operated normally.
I'm hoping ammo was at fault. It was Hornady Black, and I've never had anything like this to happen b4. But what do you think could have caused it?

 

[Dosh]

Perhaps the ammo, hoping it's not the head space or chambering. Try different ammunition or hand load some first. Then have the smith look at it. I have seen Hornady brass on the soft side but not new first firing. Good luck

 

[ar10ar15man]

pull and inspect your firing pin
call and talk to hornady

 

[woodnut]

Thanks, guys. I am baffled and still wonder if those 2 pieces of ammo were "defective". I will check the firing pin and write Hornady. I doubt they will confirm they sent out "bad" ammo, but maybe...
ON purpose, I did not shoot my reloads, but now think I should have. Will also do that. When I get it figgered out, I'll let you know!

 

[lancetkenyon]

"2 out of 6". 33% were overpressure for your rifle. I would not shoot those again. Gassers don't like as much pressure as bolt guns.

Did you shoot over a chrono?
Did you measure a new case vs. fired case?
Did you measure CBTO on a few other unfired rounds to check for consistency?
Try a different ammo?

 

[mudygmc]

My brother has a Dpms light weight hunter in 260 rem. Factory ammo I believe it was 120gr federal were fine. He loaded some berger 130s to mag length and was blowing primers at 42gr of h4350. Closer inspection showed that the bergers were jamming the rifling. Setting them back made all the difference. No more blown primers at 45gr even. I recently had a 6creed barrel built for a savage. When ordering the barrel there were two options for freebore. I don't remember the specs offhand. But say one was like .087 for most all ammo. The other was .1xx for hornady ammo. I bet you any money your jamming the bullet and switching ammo or handloading will cure the problem. To try take a Sharpe and color the bullet. Then chamber the round and remove. Odds are with hornady ammo you will have rifiling marks on the bullet. Good luck figuring it out. Hope this helps some.

Adam

 

[misterc01]

Re-read he above. Excellent advice. One reason I ALWAYS check and verify max bullet seating depth to avoid jamming into the lands.

 

[Core781]

Recently, I had an AR10 rechambered by a fine smith from 6x47Lapua to 6 Creedmoor. Went to test and zero it and two factory rounds had their primers blown out. Inspecting the primers showed no other pressure sign, but was black round it and the pocket was all black. Only two out of maybe 6 rounds. Other fired cases showed no pressure signs. Rifle operated normally.
I'm hoping ammo was at fault. It was Hornady Black, and I've never had anything like this to happen b4. But what do you think could have caused it?

I have finish cut pistol chambers before (1911/M9) on Barsto barrels. My thoughts are to check you chamber first and ensure it's up to spec. Ask your smith to gauge it for you. If you don't have a chamber micrometer, you'll need three chamber gauges. Check with your bolt face. If that checks out.

Measure your firing pin hole and verify it's kosher. And check the firing pin.

Sometimes new chambers can be finnicky for 50-60 rds. better to be tight than loose: if that's the case you'll need a new barrel. Dont shoot if it gauges out of spec.

 

[woodnut]

I think we have a winner! I just ran a couple rounds into the chamber and lo and behold, there's a "scuff" mark all the way around the bullet just ahead of the brass. Doesn't look like rifling, more like throat? Or neck? Nothing discernible on the brass. So, I'm going to re-seat the bullets a tad deeper and see what that does. I will also go back to my 'smith and let him run some more tests. I think we need to do some more in chambering. I really appreciate all your help! Getting old is tough; I forget ... where was I? And then I did....who are you? Darn it! I have a bad case of CRS! LOL. But life is still great!

 

[woodnut]

Just stuck one of my reloads in the chamber and it only had a very, very faint mark on it. Same place, and mostly all around, but very, very faint. I think I like that. I'm hoping ether we can do something easy in the chamber or I'll just seat the bullet in my reloads deeper til no marks. Odd though, that there wasn't any other obvious pressure signs on the case heads. I have chronoed the ammo, both factory and reloads in my bolt rifle, and didn't see any pressures and velocities were 3100fps range or less. so I'm pretty convinced the chamber in the AR is tighter and /or shorter.

 

[mudygmc]

Kind of what my brother went through. He just seats bullets deeper. He didnt see other pressure signs either really. Surprised hornady factory ammo is so long. Disnt know anything about it until I was told about the different freebores when i ordered my barrel. ARs will mark bullets feed8ng too. So if your mark is all around I might seat it a touch deeper. No issue unless your looking for max case capacity. Sounds like your on the right track. Glad to hear

Adam

Just stuck one of my reloads in the chamber and it only had a very, very faint mark on it. Same place, and mostly all around, but very, very faint. I think I like that. I'm hoping ether we can do something easy in the chamber or I'll just seat the bullet in my reloads deeper til no marks. Odd though, that there wasn't any other obvious pressure signs on the case heads. I have chronoed the ammo, both factory and reloads in my bolt rifle, and didn't see any pressures and velocities were 3100fps range or less. so I'm pretty convinced the chamber in the AR is tighter and /or shorter.

 

[woodnut]

Love the KISS method! I just checked my reloads and they are seated deeper. I then seated the factory to that depth and no marks. So next is to the range to see if it works. Wish me good luck!

 

[canuroper]

Changing seating depth (deeper) on an established load without work up may change pressures? Be careful altering factory loads.

Glad you are on track to solving your issue.

 

[woodnut]

canuroper, I agree that I could be spiking pressures by seating deeper. Not 100% sure this is the answer, but worth a try. When I chronoed the factory and my reloads, I saw no pressures (in my bolt rifle). Vel. was comfortable at 3100fps. Accuracy was outstanding,too. So I may be ok seating deeper, may not. Just trying a few of each and also in my bolt rifle. I did record the old and new seating depths in case Murphy raises his ugly head. In that case, back to the drawing board!