Blown Primers in AR

[StringTwelve]

Went to the range today to work up some loads. With some of the hotter loads (still under max suggestions) I had 5-6 blown primers. Not pierced, the primer actually blew out. The brass was LC 07 and LC 08. My friend was also shooting the same load tests with literally the same 24" bushmaster as mine and had zero issues. I've noticed before that my brass has had some decent gouges like it's under pressure when the cam rotates but thought it was just needing to be broke in. Now it's all making sense.

Any suggestions? I think this is actually a gun issue and not the loads themselves. I've got a few ideas to try but wanted to know if anyone has run into this issue before.

Gun Profile:

Bushmater 24" fluted free float barrel.
Bought at gun show with approx 200 rounds through it (condition appeared to confirm this.)
Ran 300 rounds through it before blown primers
Full length buttstock
Rifle buffer

 

[unwise11]

You might want to change the title because I doubt the mods will find it funny.

 

[FC]

You might want to change the title because I doubt the mods will find it funny.

Huh?


OP, obvious pressure issue? You might even want to check the headspace on your rifle.

 

[rsrocket1]

What was your:
bullet type/weight
powder
charge weight
Cartridge length

 

[jim243]

First thing that comes to mind is that the primer pockets were swaged too large when removing the military crimps. Since I have the same rifle the only time I have had a blown primer was when the primer pocket was too large.

Jim

 

[StringTwelve]

It happened with several different loads, the hottest being 27gr of H335 behind a 50gr V-max. OAL was something like 2.280 (about .070 off lands).

I'll try the same loads with some different brass and see if it holds up any better.

 

[TexasRifleman]

You might want to change the title because I doubt the mods will find it funny.

Why change the title? Blown primers are not exactly an uncommon occurrence.

Anyway, back to the topic. Blown primers can happen with brass that's worn out or where the primer pockets were reamed out too much, happens a lot with milsurp brass like jim243 mentions.

Might not even be anything wrong if that's the case. Did you load these yourself? Did the primers feel resistance when seating them?

 

[StringTwelve]

Yes, loaded myself. The only thing that's odd though is that my buddy (who I load for) was shooting the same rounds with the same brass and had no issues. I'll try and take some pictures of the brass to show the gouges the bolt is leaving on some of the rounds. They show a lot of pressure present on the back of the brass as the bolt rotates.

As to the title issue, I originally had the title as "Premature Ejectul... in AR". Thought it would be funny... the mods changed it for me though. Live and learn. Sorry if I offended anyone.

Anyhow, back to guns an ammo....

 

[APIT50]

Really need pics of brass to get a good idea of what is going on. However, as someone mentioned already, could be headspace issue. Are you seating bullets past magazine length "too far into the lands"? Maybe timing issue? (bolt unlocking early)?

 

[StringTwelve]

All my loads are at or under mag length. All my overall lengths have been determined using the Hornady OAL gauge for each bullet. I'm thinking it's unlocking early because of the occasional concentric gouge. I'll get some pics and post them tonight after work.

 

[nbkky71]

I had this issue once and it turned out to be the brass I was using. I was shooting 77gr and 80gr SMK bullets over 24.0/24.5 gr of Varget (respectively) in a NRA/CMP A2 service rifle upper (Wilson barrel). Not a hot load at all, but I was still schucking a lot of primers.

I swapped brass and the issue went away. This was the old "FC" marked Federal .223 brass, which is generally regarded as being soft. I couldn't tell any issues when seating the primers, as I could still feel resistance, so I didn't think the pockets were loose.

 

[Slamfire]

The speeds Highpower Competitors are pushing their .223 bullets, you would figure that they all would be blowing primers each bullet.

You might have a tight barrel, regardless, cut your load by a half grain. If that blows primers, cut it another half grain. Continue reducing the load by a half grain till the primers stay in the pocket.

Not elegant, but it works.

I was amazed just how much powder I had to cut my load in my Krieger barreled rifle. This is not anywhere a max load in the reloading manuals, but at 22.0 grains, it blew primers.


CLE Flattop, 24" 1:8 Kreiger Barrel
69 Sierra 21.5 grains N135 LC mixed WSR (Brass) 2-Jul-04
OAL 2.25 T = 80° F
Ave Vel = 2818
Std Dev = 20
ES = 70
Low = 2776
High = 2846
N = 10

 

[Shawn Dodson]

You may have a .223 chamber.

Your friend may have a 5.56mm chamber.

 

[Welding Rod]

Would powder burn rate be a factor? I wonder if a switch to a faster powder may help?

I was shooting PMC 55 grain in my 20" BCM upper yesterday and most all the primers backed out, but none entirely.

 

[APIT50]

Faster powder equals more pressure usually.

 

[Welding Rod]

The reason I ask is supposedly on a M1A slower burning powder is a no-go as the pressure can still be too high when the gun starts unlocking.

I am wondering if a similar condition could happen in an AR?

 

[Slamfire]

The reason I ask is supposedly on a M1A slower burning powder is a no-go as the pressure can still be too high when the gun starts unlocking.

I am wondering if a similar condition could happen in an AR?

Primers backing out is usually due to light loads, not slow powders.

The first thing that happens on ignition is that the primer backs out and the front of the case grips the chamber. Then as pressures build the case stretches in the middle, stuffing the primer back in the pocket.

If pressure is not high enough to stretch the case, sometimes you will see backed out primers.

The load I used here was 150 SMK 47.5 grains IMR 4895 CCI #34 primers. The primers backed out in my Sako (I think)

Not evil at all.





Too slow of powders in a gas gun will lead to case ruptures and excessive case stretching as the gun will unlock when residual breech pressure is too high. Its all about timing. It is better to use faster powders than slower powders in gas guns.

 

[Welding Rod]

Hmmm. Interesting. Looks like the cases that came out of my BCM AR on Sunday... the primers backed out of the factory loaded PMC 55 grain cases about like that.

On those same cases I found the post-firing headspace dimension varied by about .008". From about .002" under max unfired to .006" over max unfired. That seemed like a pretty extreme spread to me.

 

[Shawn Dodson]

See - http://www.m-guns.com/tools.php

Click on ".223/5.56? Gage" and "5.56 Reamer"

 

[StringTwelve]

Sorry for the slow response. The boss came in town and my work load doubled. Here's the pics. (True to the title, these are blown. I did not remove these primers myself.)
I did not swage these since the primer crimp was mild. Only slight reaming on the mouth to allow primer entry.

 

[Rottweiler]

I see extractor and ejector marks on the case heads. I'm thinking WAY too much pressure. Back off a half grain or more

 

[mc223]

Any suggestions? I think this is actually a gun issue and not the loads themselves. I've got a few ideas to try but wanted to know if anyone has run into this issue before.

I have lost a few primers in a match rifle from pushing the loads too hard. Those look a tad warm to me too.
Your rifle may be a bit over-gassed by comparison to your shooting buddies rifle. That is why you must work up loads for your gun. No two are the same. (OK so what are the chances that two that are the same are actually in the same place at the same time)


David Tubb sells a device called Carrier Weight System. It basically delays the bolt unlocking before the pressure drops in the gas system. It can reduce damage to the brass as in excessive stretched primer pockets and blown primers. Also reduces case stretch and extraction damage.

http://www.superiorshootingsystems.com/AR_15_PRODUCTS-AR_15_Carrier_Weight_System.html



o

 

[M1key]

Overpressure for sure.

I load LC brass down a bit more than commercial.

Your rifle may have a tighter chamber than your friends. Possibly .223, which usually has less headspace than a 5.56 chamber.

I guess all ARs are NOT created equal.

M

 

[Slamfire]

Way darn overpressure.

Cut your loads.

 

[StringTwelve]

So why would stock M193 and Aguila .223 ammo make the same grooves on the brass? They didn't blow primers but it's obvious something isn't right overall. I think I'll give the carrier weight a try first.