Slamfire or ???

[sschudalla]

I could use some input regarding an issue I am having with my DPMS LR308AP4. I am a relative newbie in the AR world but have been shooting my whole life so my knowledge of the AR platform is limited--but growing rapidly!.

I have encountered an in battery double cycle (I think) a handful (5 or so) of times with this rifle after I have run about 250 rounds through it. I am using both new ammo off the shelf--Remington Core Lokt and bulk Winchester ammo, 147 gr FMJ. I have also used my own reloads and encountered the same issue. I have looked into the liklihood of a high primer issue but all seems to be on the up and up with primers sitting at least .003" under the casing when I measured it with my caliper. I am using CCI No. 200 primers in my own reloads per the manual. I have not tried out the CCI No 34's yet but I have about 200 of them sitting around for reloads. (If you guys think this is a slam fire issue---I will give them a shot with reduced charges) I verified the fact that the primer is being struck hard by ejecting a cycled round manually and there was a definite imprint on the primer. Also, I can say the frequency of the double cycle is definitely higer in my reloaded ammo with it occuring twice out of 50 or so rounds.

On my last trip to the range a week ago, I noticed an issue with the trigger assembly pin (theres two in the lower, I am talking about the one nearest/above the trigger) walking out of the side of the lower receiver frame too. As I look back on it, this pin always sat proud of the lower and I thought it was just supposed to be like that. Also noticed the whole trigger assembly could wobble. I broke it down and was able to carefully get it seated flush and now I cannot push it out--seems like it is set right now.

What I am wondering is what you guys think I should do next. Obviously, I do not want to take an "unsafe" rifle out to the range. (As I consider it, a rifle that discharges two rounds that I intended on one is unsafe!) However, if it can be cured easily enough with a stronger primer or if you think the pin walking out issue was the cause I would like to try it again without parting with it by sending it to the factory.:banghead: Hopefully the trigger pin walking out could cause this and I have likely fixed it. I am craving another trip to the range!

Any help you guys could offer is really appreciated.

 

[Bartholomew Roberts]

You need to perform a function check on the rifle to be sure the fire control group is operating correctly.

Unload rifle and disassemble lower from upper.

1. Cock hammer and place selector on safe. Pull trigger. Hammer should not fall.

2. Cock hammer and place selector on fire. Pull trigger and hold trigger to the rear. Use your free hand to catch the hammer and stop it from slamming into your receiver. Hammer should fall. After hammer falls, continue to hold the trigger to the rear and cock the hammer again with your free hand. Release the trigger. Hammer should not fall.

Doing that function check will help isolate whether the problem is your rifle slam firing or whether the problem is a result of out-of-spec/worn fire control group.

Also from your description (pins walking out), it sounds like the hammer pin spring is not properly installed as well.

 

[sschudalla]

Thanks Bart! Just conducted the function check as you described and it is working correctly. When I do conduct step two, there is a click after I release the trigger but the hammer does not fall. It is only when I pull it from post release forward position that the hammer can fall. Looking over the exploded assembly diagram, it looks like the hammer pin spring should hold the pin in place by fitting into a groove on the pin (??havent seen this but looks like possible??) I cant push that pin out anymore. Anything else I should do? Thanks for the help.

 

[Bartholomew Roberts]

When I do conduct step two, there is a click after I release the trigger but the hammer does not fall.

That is normal. As you release the trigger, the disconnector (which is what grabbed the hammer) lets go of the hammer hook and the nose of the trigger catches the hammer notch. That makes the "click" you are hearing.

The good news is it doesn't sound like your fire control group. The bad news is I don't know what might cause an AR10 to slamfire as you describe. You may need to give DPMS a call.

Looking over the exploded assembly diagram, it looks like the hammer pin spring should hold the pin in place by fitting into a groove on the pin

Yes. That is correct.

 

[sschudalla]

Thanks for your help. I at least now have some confidence that the standard function check shows that the fire control group is functioning properly.

 

[Sky]

Ok there are some threads about double pop and even 4 pop. These were new ARs one was a Bushmaster and One was a Del-Ton. The Del-ton trigger was honed down to much during deburring and assembly. The Bushmaster fixed itself after 50 rounds? Both were trigger problems. You may have fixed your problem already.

 

[Tim the student]

Bart, what is the benefit of doing the function check that way, instead of the "Army way"? Just saving some wear and tear?

 

[Bartholomew Roberts]

Bart, what is the benefit of doing the function check that way, instead of the "Army way"? Just saving some wear and tear?

I like to remove the lower from the upper so I can visually see what is happening. It isn't necessary to do the check; but I find this way is less confusing for new shooters who may not be able to tell whether the "click" was a hammer falling or just the trigger nose catching the hammer.

 

[P-32]

If your squezzin' the trigger like you would on a pistol, you might be what's called milking the trigger which is a trigger pull during recoil. I have not seen many of these in a AR but have seen and done lots with a M-1 or M-14.

Since you are reloading I would not use Winchester or Federal Primers. CCI and Remington 7 1/2's work very well in the AR.

 

[Tim the student]

Thanks Bart.

 

[Jeff F]

If your squezzin' the trigger like you would on a pistol, you might be what's called milking the trigger which is a trigger pull during recoil. I have not seen many of these in a AR but have seen and done lots with a M-1 or M-14.

Basically, an accidental bump fire. I've seen it with an M-1 a time or two. Don't NATO rounds use a harder primer? I don't own any AR's but thought the firing pins were pretty light and with the rotating bolt would not carry enough momentum to slam fire.

I had a magazine fed sks jamb its firing pin one time and go full rock & roll, dumped about 20 rounds down range before I could blink. I'd rather not have that experience again.

 

[jerkface11]

I've seen it done on an AR more than once. Usually with a light trigger. Start following thru with your trigger pull and the problem will go away.

 

[sschudalla]

Thanks to all. I will give the advice a try at my next range trip. I definitely may be squeezing that trigger like I shoot my pistol..Typically I pull and hold for a split second second or two after recoil. I could see how an accidental bumpfire might be my problem. Will work on my technique for sure and give the CCI no.34's a try.

Another thought I ran across, I have been reading a lot about cleanliness of the bolt carrier group possibly affecting/increasing this problem (most threads are talking about this in a SKS) so I gave it an even more in depth scrub down than I have been. Have been using CLP. One thing I noticed I missed in my shoddy prior post range cleaning is a lot of tiny bits of brass inside the bolt itself, under the ejector, etc. Removed all of it, every last spec. Is this normal for brass to be present in the BCG? I have been reading the Sierra reloading manual section on service rifles and they seem to think so..not specifically but they discuss the "nature" of a service rifle and its propensity to not be real nice to brass. Thoughts?

 

[TScott]

I don't have any experience with AR-10's bolt carrier assembly, (lots with the AR-15), but could this also happen with a slightly longer than spec firing pin? All primers are impacted by the pin when the bolt is closing, but not enough to set them off, I would think a longer pin might have enough force to set off the primer?

I could be completely wrong, but that was the first thought that came to mind

 

[Bartholomew Roberts]

The brass extrudes into the ejector/extractor under pressure and they will shave off tiny bits as they operate. Some tiny shavings are normal; but that can also be an early sign of higher pressures in the chamber/timing issues. Typically your symptom of higher pressures/timing is that the ejector bites off enough brass that it binds the ejector.

 

[sschudalla]

Thanks again fellers... I think the BCG is really, really similar to an AR15. This is my first AR so dont quote me. I am certain there are minute dimensional differences but that is it.. Firing pin mass could certainly do it if enough inertia=pin weight but I wont be figuring that one out anytime soon! I definitely get a good size dimple on rounds that dont fire and havent been intended to fire, just normal cycle. I am told thats perfectly normal.

Bart, the brass is tiny..real small flakes really. I dont have any definite high pressure symptoms yet. Will keep my eyes peeled for that though. One that could be by a stretch (but I dont think so) is a unique scuff on the backside of the shell, next to the primer pocket on the rim. Normal in a AR?

 

[bbuddtec]

Ok, I think you fixed your trigger, and I think your extractor is workin the brass over... bolt face printing is normal. all seems normal and I would go to the range and be aware of the follow thru jerkface mentioned.... but that's just me

 

[jerkface11]

A buddy of mine had an AR set up for target shooting with an extra light trigger. You couldn't shoot a good group with it because it was so hard to get a single shot out of the thing. If you did it right you could empty the whole mag.

 

[sschudalla]

The stock DPMS trigger does not seem overly tight to me, has a little slop if anything. But, have only shot a couple of AR's and no AR10s until mine. I have a cheap desert plinker AK with a tapco trigger that is way tighter than the DPMS stock set up--but again, not super experienced for AR "feel" yet. Its not bad, just darn sure not a hair trigger. I decided the best course of action here is to bring a box or three of new ammo out, different brand (any better off the shelf than others??), give it a run over 60 or so rounds and make a decision. First double pop will mean end of the day and a call to DPMS. I agree that the fire control group is okay for sure. Will pay close attention to my method and will be sure to share any info I uncover with the thread members.
PS--Probably will start out with very composed three round clips and get some good groups to gain some confidence (and so I dont rock a 19 round burst downrange--whoosh!!)

 

[Bartholomew Roberts]

Bart, the brass is tiny..real small flakes really. I dont have any definite high pressure symptoms yet. Will keep my eyes peeled for that though. One that could be by a stretch (but I dont think so) is a unique scuff on the backside of the shell, next to the primer pocket on the rim. Normal in a AR?

The brass shavings sound normal. I haven't noticed the scuff mark you mention; so I can't comment on that; but I am more familiar with AR15s than AR10s.

 

[Slamfire]

The good news is it doesn't sound like your fire control group. The bad news is I don't know what might cause an AR10 to slamfire as you describe. You may need to give DPMS a call

I don't have a DPMS AR10 rifle. The whole firing pin mechanism is larger than a AR15, I have seen the rifles.

Back in the day when people shot M1a’s in highpower, you saw doubling. These occurred in the rapid fire sequences and were 100% due to bad trigger jobs. Too much material had been removed from the sear surfaces and the hammer followed the bolt forward. We would give the guy a second chance on the alibi string, and 100% of the time the rifle would double again, within the next ten shot string, and then we would tell the shooter to get that rifle off the range.

Mechanical problems don’t just go away. If your rifle is not doubling at least every ten rounds, you don’t have a sear engagement issue.

We heard of out of battery slamfires. These were very rare. I met a guy who had an out of battery slamfire with an M1a and the trigger mechanism was not at fault. It blew his rifle all to heck.

If everything is fine mechanically, then you have a primer issue.

Any mechanism with a free floating firing pin has the potential to “slamfire”. If the moving firing pin has enough energy to ignite the primer, when that firing pin bounces off a primer, that primer is going to ignite.

You would think that is obvious, but people just don’t want to acknowledge that it can happen.

Commercial primers are more sensitive than military primers. That is actually bad as military weapons tend to have heavy firing pins.

Mike Venturino in a recent rifle magazine mentioned he had slamfires in his Russian SVT 1940, and shows a picture of the round with a big dent in the primer, and also had a slamfire in his German G43. Both of these rifles must have heavy free floating firing pins.

Winchester primers were changed in 1999 to make them more sensitive. The brass finish primers also pierce easily.

A gentleman posted these pictures of Winchester factory ammunition that slamfired in his gas piston AR. The rounds on the top are the slamfire rounds.



I would talk to DPMS about your experiences and see if others are having the same problem. If your bolt does not have a spring on the firing pin, it should. That spring is there to slow down the forward movement of the firing pin. Slower firing pin, less energy on the bounce. When Armalite took the firing pin spring off on their AR10, they had slamfires with LC ammo. Turns out that the primers on LC ammo have been getting more sensitive. They put the spring back on.

 

[sschudalla]

I heard Armalites ran with a spring on their firing pin. DPMS does not for some reason...I have no idea why--seems like a better design. Love the rifle and its quality but this issue has me a little peeved and still scratching my head--could be ammo or shooting procedure. Tried to call DPMS today, didnt get through. Based on good function of the parts, proper function of the fire control group, cleaning and full inspection of the firing pin and BCG, I am going to run some new rounds at the range--also will give CCI #34 primers a run. Will watch my shooting method carefully. Will get back and let you know how it goes. Thanks for the photo, those slamfire rounds look damn close to what I cycled out manually post firing. I appreciate everyones thoughts.

 

[Slamfire]

Thanks for the photo, those slamfire rounds look damn close to what I cycled out manually post firing. I appreciate everyones thoughts.

If you could post your pictures, I for one, would be appreciative. Slamfires are exceeding rare and it would educational for everyone if we could see the slamfire rounds.

 

[chrome_austex]

I agree, if you can collect some chambered, but unfired rounds to see how much the firing pin is denting the primers when when it chambers a round under recoil.

Basically load up a mag, shoot a shot, and then eject the newly chambered round w/o firing it and take a picture of the primer.

My AR will put little firing pin marks on the primers, but not enough to slamfire (so far, anyway)

If you can post a few pictures of your chambered rounds, then we could probably say if it looks like there is excessive firing pin contact with the primer or not.

 

[sschudalla]

OK--I will do that next time I go to the range, likely this weekend. (I didnt see the request until Sunday night and I was there on Saturday) I did actually perform a check Saturday using the #34 primers and inspected the dimple--still present but far diminished from before. I will be glad to get a photo up for everyone though with both styles of primers. On a side note, I ran 100 or so rounds through this saturday and not one issue! Reloads and new ammo performed very well so I am a real happy camper. I think all the tips from you all were really helpful. If anything else develops I will let you know and I will also get some pictures up soon.