Slamfire in my DPMS

[sandog]

Yesterday I was shooting my Oracle .308 and had a slam fire. I have been shooting since I was 12, 45 years ago, and enlisted in the Army in 1975. I've shot a few rounds through self loading rifles. But this slamfire was a first for me. I was using Hornady brass, Winchester LR primers and W748 powder under Hornady 150 gr. FMJ  bullets. I was certain that all primers were seated below flush, I check twice before charging with powder. I was under the impression that Winchester was a harder primer, but an aerospace engineer friend told me the Winchesters were very hard when they still used a nickel cup, but since switching over to a brass one they are now one of the softest. I went to several stores yesterday looking for CCI #34 primers but there were none to be had. My friend told me he has dissected various primers, and to him the CCI 250 mag primer is essentially the same as the #34. I will try some of those until some of the #34's are in stock here. I might add that the round fired when I hit the bolt release to start off another 5 round string. I would think the bolt velocity would not be any more than if the bolt was cycling from a previous shot. The DPMS rifles do seem to have tighter chambers than others I've fired. I have had no chambering problems in my .308 when sizing with a regular Full length die. Another friend, who bought a 5.56mm Oracle when I bought mine, was having problems with the bolt seating fully using brass that he full length sized. ( and O.A.L. was correct.) I checked the rounds he loaded in my L.E. Wilson cartridge gauge, and all inserted fully, no tightness. His is the first semi-auto rifle I've seen that might actually need a small base sizer.

So far, I have swapped out the factory stock and grip for a Magpul ACS and Moe+ grip, Got  the trigger down from 7 1/2 pounds and gritty to 5 pounds and smooth, a Troy Medieval muzzle brake, and added an ambi safety, Norgon ambi mag release, P.O.F. Rattler ambi charging handle to make it more "Lefty friendly". Next up will be some Troy or Samson BUIS, an adjustable low profile gas block, heavy buffer and spring, and an Apex F.F. tube, and eventually a better aftermarket trigger that doesn't have a mile of pretravel. Still trying to decide about an optic to replace the cheap 2-7x shotgun scope that on there now just so I can have some sights to get out and shoot it. Thinking about getting a Leupold VX-R 3-9x with Ballistic FireDot.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I was shooting Hornady 150 FMJ's in Hornady brass with W748 powder, and Winchester LR primers. I had started another 5 shot string and hit the bolt release to chamber a round. The carbine fired when the bolt slammed forward. It was angled down and to the right when it firedslightly in relation to the target frame, and just missed hitting the tripod my chronograph was sitting on.

Edited June 30, 2015 by sandog

[survivalshop]

  You say you got the Trigger pull down to 5#'s , what did you do to it ? The MilSpec Triggers & Hammers will not take much of any altering & the Sear engagement surfaces. They are known to have problems when altered , even a little . Surface Hardness is very shallow & suspect . 

 

  Is this the first problem with this rifle ? What is the round count ?

 

  You could have a Disconnector problem also , for the same reason . They will double fire or slam fire or go full auto with no stopping until the mag. is empty .

 

  If you want a good , inexpensive FCG , ALG , ACT trigger ( FCG  ) is a very good one , can be had for about $ 60-70, Mine have leveled out at around 5# & since they are made by a company owned by the wife of Geissele Triggers , he knows triggers & one of the best around . 

  If you don't mind spending around $100, there is a group buy in the Coupons section at the very bottom of the Thread list for a MechArmor Modular FCG , single stage & a heck of a buy , I have two & they have a clean break & have one of the fastest resets I have seen in a Trigger system .

  This is a Very Dangerous condition & should be taken care of immediately , of course I didn't have to tell you that. <thumbsup>

 

  I have a Rem. 870 mag. that is my designated slug gun for Deer hunting ,I sent out to have the trigger pak to be gone over , to a very well known Trigger smith & it was great for about four seasons & we had just finished a Deer drive & we were standing around waiting for everyone to get bak & I had the DSG on a single point sling off to my side , just hanging there & it went off into the dirt . I emptied all ammo from it & checked it out , that thing would drop the hammer if you just blew on it . I pullded the trigger pak out & the Hammer Sear had sheared off in the middle . Lesson learned , the Factory Trigger groups are not made to be altered , any more , no matter who makes it .

   I put a Timmney Trigger fix in a new Factory Trigger Pak & she has been working just wonderful , not as great of a Trigger pull as the Trigger job , but I feel much safer . Always keep the muzzle in a safe direction , but you knew that .

 

  DPMS 308AR's are notorious for tight Chambers , if you haven't had problems in the past with Chambering , the FL sizings die should be fine . I would cheek the Head Space , just fore the heck of it & make sure the Chamber is clean , scrub it with a brush .

 

[sandog]

No, without a jig or fixture I know to not do anything to the engagement notches. I did a light polish on the big shelf atop the trigger and the pin holes and sides around the holes with jeweler's rouge on a felt Bob. I switched trigger and disconnect or springs for red JP springs, but kept the stock hammer spring in there. About 200 rounds through it with no other problems, all my hand loads, no factory.

[98Z5V]

If it's truly a slamfire and not any other kind of mechanical malfunction...

 

This is exactly why Armalite uses a firing pin spring in the AR10.

[sandog]

That's great that the Armalite has a firing pin return spring. Too bad I don't own one. An AR-10 that is. I do own an Armalite 5.56mm.

Edited June 30, 2015 by sandog

[98Z5V]

I don't own an AR10, either - don't want you to think I was brand-bashing, because I'm not.  I'm just pointing out exactly why Armalite does that in the big AR, and that's the only reason they do it. 

 

Are you positively sure that your hammer was still in the cocked position after the slam fire?  Positively?  Meaning, you specifically checked that the hammer was still locked down/back after this thing went off when the BCG went forward?

[survivalshop]

   Check your FCG for any brass shavings or anything else that could cause a problem . Check the BCG firing pin passage to make sure the firing pin is not hanging up or sticking also.

 

  You say you changed the Trigger & its spring, how about the Disconnector Spring ?  Is it in correctly & the right one ?

 

    When you say you polished the pin holes & their openings , were you talking about the Pin holes in the Hammer & Trigger ? Not the Receiver Pin holes ?

 

    Too weak of Trigger spring can also cause problems. I'm going to assume this happened after you changed the Components & spring ?

 

    There are literally millions of rounds fired from AR's with out a firing Pin return spring , with out slam fires . It would be nice to have one though , just about every other firearm has them .

 

    It is usually something in the FCG that is not doing its job of Sear engagement or being prevented from doing so . 

 

  You could still of had a high primer also & missed it , it happens . 

 

   Give everything a good cleaning & inspection & re-test the FCG before taking it to the Range after cleaning .

Edited July 1, 2015 by survivalshop

[sandog]

Hammer was in the cocked position ready to fire again. No shavings in the FCG or in the firing pin channel, I took out the firing pin and cleaned the channel when I first got the rifle. Suppose I could have missed a high primer but not likely, as I said I check them all after priming  and again going into the loading block before powder charging. I polished the trigger and installed the red JP trigger and disconnect spring when I first got it, and have fired about 200 rounds the last few weekends. I did not polish the pin holes in the receiver, only holes in the trigger and hammer, and only very lightly.c

Gonna try harder primers when I load again. 

[98Z5V]

 I did not polish the pin holes in the receiver, only holes in the trigger and hammer,

 

Never, ever any need to polish the trigger and hammer pin holes in the receiver - ever.  Don't even know why that thought would even occur.  Have no idea, either, why you'd polish the holes in the trigger itself, and the hammer itself.  Where the hell did you even hear about anything like that?

 

That might be your very problem.  You increase the diameter of the hammer pin hole in the hammer, and you give the hammer "flex," and room to move where it normally doesn't.  Same with the trigger pin hole in the trigger and disconnector - more movement.  Before you know it, you just fucked with your disconnector sear to the hammer... 

 

Boom.

 

$hit can that trigger, try something else.  Or, take that thing back out to the range and try to get it to fire again, just by releasing the bolt catch.  And observe the trigger/hammer again.

 

Also, before you get all pissed off and butthurt about the info presented - this isn't our first rodeo.  There's a bunch of smart fuckers here, including gunsmiths, asking you questions, and the answers aren't adding up. 

 

I can't even tell you the numbers of rounds myself, and very good friends, have launched from DPMS-pattered 308ARs, and never, ever had a slam-fire.  That even includes Mike's crazy $hit.

 

You need to look at that trigger work you did, get that thing out of there, and try something else, stock and unmolested.

[sandog]

Yes, as soon as I can afford it, I am getting rid of that stock trigger ( and getting a F.F. handguard, and heavier buffer spring and adjustable gas block to tone down the excessive gas). I had to do something to the stock trigger as it was the worst trigger I've ever ran across. I am not offended by any of the suggestions given out, I posted this on here to get other's opinions.

I spent maybe all of 3 seconds with the felt bob on the pivot holes in the trigger and hammer, I doubt I enlarged them or even smoothed them, if at all. I heard about smoothing the holes to eliminate friction from manufacturing burrs from Patrick Sweeney. The trigger has functioned fine for 200 rounds, just when I hit the bolt release and the bolt slammed home did it fire. 

I've considered all the things mentioned as possible causes. There was no obstruction in the firing pin channel as someone else mentioned. I would think that debris in the channel would impede the firing pin movement and cause light strikes, not unintentional ones. Primers were seated to the bottom of the pocket with an RCBS hand tool, and checked twice before loading. Trigger was function tested after polishing.

This is my first .308 AR, but I have had a dozen in 5.56mm, not counting ones issued in the Army. I've fired probably 10,000 rounds in those. 

I do have a Remington R-25 in .243, shot it for close to 2 years now. It is essentially the same rifle, being made by DPMS. It also had a less than stellar trigger, I smoothed /lightened it as well, before I could afford the CMC trigger it now has, and it has always fired the same Winchester primers that I was using in the .308 last Saturday.

[Toolndie7]

Are you positively sure that your hammer was still in the cocked position after the slam fire?  Positively?  Meaning, you specifically checked that the hammer was still locked down/back after this thing went off when the BCG went forward?

 

the slamfire round probably would have cycled the action and reset the hammer.  Sounds like you guys are right going after the trigger Vs anything else

[98Z5V]

 There was no obstruction in the firing pin channel as someone else mentioned. I would think that debris in the channel would impede the firing pin movement and cause light strikes, not unintentional ones.

 

The possibility of debris in the firing pin channel could have held the firing pin forward, forcing it into the primer, instead of just lightly bouncing off the primer.

 

I've noticed in 5.56 rifles - alot - you chamber a new round from a fresh mag, using the bolt release.  Pull the round, check the primer, slight, small dent.  Not enough to set it off, but enough to let you know that it contacted.  Militarily, we'd go through several rotations where we'd chamber a round, only to unload and clear later.  What do most people do? Pop that pulled round right back in the top of the magazine...  It's only gonna get chambered soooo many times before it gets popped.  I always made my guys rotate that pulled round lower in the mag, and always check the top round to make sure it hadn't been chambered before. 

[sandog]

I did some searches on slamfires and primer sensitivity, and there were references to problems with the newer brass cup Winchester primers in service rifles. Federal seem to be the most sensitive, with Winchester a close second. Least sensitive were CCI. There is no debris in my firing pin channel, I did not enlarge the holes in my receiver ( pins are still very tight!), no high primers. One thing I remembered from the shooting session last Saturday was: I had been loading 5 rounds into the magazine to fire groups with each powder charge, but the only magazine I had was a 25 round Magpul Pmag. Way too long to shoot from the bench. I was having trouble raising my shooting rest up enough to clear the long magazine. When I finished shooting the 150 FMJ's, and started shooting some 165 SST's I had loaded, I quit using the magazine and started hand chambering the round. I don't remember easing the bolt forward, so was probably letting it slam forward by pushing the bolt release. This would incur more bolt velocity as the bolt was not having to strip the round from the chamber on it's way forward. I will not do that again. Don't know what I was thinking. Yesterday I purchased some CCI 250 magnum primers, which I will use until I can get a supply of CCI #34's. I also picked up a 10 round PMag for shooting form the bench. 

https://thefiringline.com/forums/showthread.php?t=461475

http://www.m4carbine.net/archive/index.php/t-12741.html

https://en.wikipedia.org/wiki/Slamfire

http://m14forum.com/ammunition/51719-federal-210m-primers-m-1a-slamfire-risk-2.html

[survivalshop]

    Dropping the BCG one a chambered round I guess could do it . I have done it before when I forgot to pack a Mag for the AR I was using at the range & never had a problem , but most say not to do it for the reasons you say . No idea what Primers I was using , I use older WW ,CCI ,Fed. & Remington primers , the only ones I buy now are CCI's .

 

   One of the reasons for a Floating Firing Pin , is its ability to self clear debris from its channel . A spring has the potential to withhold debris with in its coils , not to mention the Firing Pin floating vs it being held in a semi fixed position by a spring .

  This & how the FCG can get some Debris also is why I recommended to clean the firearm to make sure its not a foreign particle or debris causing the Malfunction .

 

  This info about how you were feeding the rifle would have helped in the beginning of this thread , but if thats all it is , its a good thing & you should feel safer with your rifle.

 

  I used to Polish the FCG Pins & anything else that had contact with another component ( except the Sear surfaces ) , but found they seem to polish them selfs when round count goes up . It helps to polish any friction to friction components . I used to do it with the 1911 Kits from Springfield Armory , way back when & it helped a little , enough to see it on a Trigger pull gage , not much , but it was all in the feel . I just think , as probably others do here, that  the MiSpec AR FCG's suck & it doesn't help enough for the trouble .

[washguy]

I got it figured out ...you are firing off the wrong shoulder   :) Wash

[arnie]

My first 308 AR slam fired on me until I discovered the builder of the upper used an Armalite firing pin in a DPMS bolt head .I changed the firing pin and just for a feel good feeling I put a spring on the firing pin .Its under the extractor .If you take a DPMS bolt head and remove the extractor you can see the channel where a spring can lay .I measured the diameter of that channel and the diameter of the firing pin and ordered a pack of springs from McMaster Carr . I have since built two more and put

the spring in those two bolt head also with no problems .

[mrraley]

ok... it's already established, the hammer was cocked back, weapon on safe, and finger was off the trigger.

 

a loaded magazine was inserted, the bolt was pulled to the rear, the bolt was released by the bolt release on the side of the rifle.

 

when the bolt lugs stripped the top round off the magazine, fed and chambered the round. the bolt stopped when it made contact with the barrel, the carrier continued forward locking the bolt into place.

 

with the momentum of the BCG going forward, the firing pin (that floats inside the bolt) continued going forward after the BCG stopped... AND... boom.

 

 

 

 

a couple things I haven't seen touched on yet...

 

check the bolt face and look at the firing pin hole.

Is it still perfectly round?

how much of the firing pin protrudes out of the hole when checked? (do this check with everything stripped down and put the firing pin in the bolt by itself)

 

How is your firing pin? look at the tip very closely and make sure it is not dimpled or have any pits in it. 

 

find out how long the firing pin actually is. 

 

Something else you might look at, and that is only if the firing pin tip is pitted or such... look at the primers of the previous fired rounds if possible. Look at how much the firing pin is dimpling those primers.  

[DNP]

My question....if all of those sequences took place, but the modified trigger released the hammer and sent it forward....firing the round....and then all natural occurring events followed and the the carrier moved rearward ejected the shell, reset the hammer, blah blah blah....? I may have missed something in here, but is there a way to prove that wasn't how he trigger was set, ready to fire again after the fact? Not trying to be a dick here( I read my post and know it sounds that way) just asking. Is there really a way to know? It seems like with a trigger that could be right on the edge reliable that you could have one bad moment and be fine the next. I've never had a slam fire, is there something distinguishable about the way it happens?

[mrraley]

if the rifle was on safe... and I was to believe it was.

 

the trigger would not have been able to release the hammer to allow it to hit the firing pin causing it to fire that way.

 

this is why we do (or at least I) believe it to be a true slam fire.

 

 

just trying to figure out now if it was reloaded ammo issue or rifle parts issue. 

[survivalshop]

  I see no mention that the Safety was on or off  . <dontknow>   

[DNP]

would there be a difference in the primer strike? I would assume a slam fire would leave a much lighter strike as well?

[sandog]

Safety was on. I fired another 100 rounds today with no problems. I'm now using CCI 250 Primers instead of the Winchester LR, and was using a 10 round PMag, As explained earlier,when shooting last week end, the 25 round PMag was way too long for the bench, I started hand chambering the SST rounds and let the bolt slam forward that way. I checked a few of the CCI primed rounds today after letting the bolt slam home on them. I extracted the loaded rounds out of the chamber and looked at the primer. I could hardly see where the firing pin left an imprint on the primer. I did not have any of the Winchester primed rounds on hand today but will do the same test to some of those next time out.

Group was shot with Hornady FMJ, I forgot to write that on the target.

300 yard gong is just below the top of the hill at the end of my range:

Edited July 6, 2015 by sandog

[sandog]

Whoops, got one photo in there twice and couldn't seem to be able to edit it out.

[mrmackc]

I hope you kept the brass from the slam fire incident, I know I probably would have shook up too much to think of that. I hope you have determined it was a Winchester extra sensitive primer, and/or a faulty trigger.

[survivalshop]

  The Safety on most rifles , including the AR family , hold only the Trigger from moving , so as to keep its Sear engagement with the Hammer Sear ( the only thing keeping the Hammer from falling onto the Firing Pin ), but if the Sear engagement is weak or compromised in some way , the Hammer will follow the BCG into breach locking & if there is enough momentum , it could slam fire . Its why its recommended not to single load a round in the Chamber & drop the BCG from its Catch onto the live round thats in the Chamber .

 

  In my post # 2 about my 870 incident , the Safety was engaged , it didn't help .

 

  Its always a mystery when you don't find any concrete evidence of an issue , you just have to follow safe loading & re-loading practices & always keep the Muzzle in a safe direction  <dontknow>

Edited July 6, 2015 by survivalshop