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Posted: 3/1/2012 1:45:54 PM EDT
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I got a cheap AR at a gun show last weekend and have been to the range twice with it so far. Total of about 190 rounds through it. I was going for low cost because the gun is just for fun. I won't ever shoot a lot at any given time and the round count will stay low. So I did not need (nor could I afford) top of the line equipment. It is a DPMS upper, flat top, 16 inch 1 in 9 barrel. No chrome anywhere. I have a 3-9 Nikon scope mounted. The lower is a PlumCrazy. I read what I could find on the lower and people who actually had one and shot it seem happy, I did not read of any problems except for the pivot pin coming all the way out once in a while.
Now the bad news. I was shooting groups of 5 rounds with 5 rounds loaded in the mag at a time. During one string I fired the third shot and the fourth round left also. The cycle time was impressive. It did not fire the fifth round until I pulled the trigger. This only happened once and did not repeat itself for about the next 60-70 rounds, which is all I shot today. I was shooting reloads at the time, 55gr FMJBT using 2230. I have fired hundreds of these rounds over the years and had no problems, I can't believe this is ammo related. The gun was cleaned and only had about 40 rounds through it when this happened. Any ideas, other than not loading a full 30 rounds in the mag. Thanks for any help Frank |
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Was the firing pin and it's channel in the bolt clean as well? that may have done it.
But most likely, it was one of your reloads. What I think happened was that on the round that doubled the primer was not fully seated. As the bolt face closed on the round it struck the primer and activated it that way. |
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Slamfire would be the absolute last thing that I would suspect. Ammo incorrectly installed FCG... sure it wasn't a double? Have you done the function check? probaly a double loose holding the stock, recoiling into the trigger finger. The 2 plumcrazy builds I shot had light trigger pull 4 lbs. maybe. they were not mt rifles. |
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I think I might have found the problem, maybe. While cleaning the gun I discovered that I now have only two gas rings on the bolt, and one of them is missing a piece. Could a piece of the missing/broken ring have gotten in front of the bolt and caused the gun to fire as the bolt closed. I can't get the hammer to release by hitting the stock on the floor or by prying on the hammer with my finger, so I really don't think that's the problem, plus it did not repeat while firing subsequent rounds. A soft hold and a double are also a possibility. I've never had one before, but stranger things have happened.
The next question is....is a one piece ring from brownells better than the three separate rings? Or is that another thread? http://i77.photobucket.com/albums/j55/cencrunner/IMAG0164.jpg Btw, here is a pic of the gun after I put the scope on. Thanks for the help Frank |
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I think a primer wasn't seated all the way.
I don't think you understand completely what a slam fire is. It doesn't have to do with the hammer on the fcg, it has to do with the fact that the firing pin is free-floating in the bolt and can make contact with the primer if the bolt is closed. Load a round into your chamber letting the bcg close with the bolt release or fire a round with more in the mag. Clear the weapon and look at your primer. Should see a light dimple on the primer. Reasons: 1. You were using hand loads. Primer may have come loose. 2. Out of that many rounds I would expect it to happen more than once. |
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Slam fires do happen. I had it happen with a CCI400. http://i245.photobucket.com/albums/gg76/gi57/Reloading/PA101989.jpg http://i245.photobucket.com/albums/gg76/gi57/Reloading/PA101990.jpg Slam fires in an AR are almost impossible. If one does occur it will be due to seriously flawed or out of spec ammunition. The round in the pictures did not fire out of battery. If it had, the case head would have ruptured or separated from the body od the case. Looks more like a magnum primer that was fired with no powder charge or bullet in the case.... or perhaps a small pistol primer fired under the same conditions. Notice the extrusion back into the firing pin hole in the bolt face. This usually occurs due to excessive pressure in a normally loaded round, but there is no flattening of the primer cup around the outside adjacent to the primer pocket. The remaining firing pin indentation in the primer appears too deep to be just from chambering the round. I have been using CCI #400 primers for many years with no problems. The nickle plating on this primer looks rougher than what I have ever seen on a CCI primer. Almost looks like it has been bead blasted. Normally their primers are very smooth and shiny. |
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Slam fires do happen. I had it happen with a CCI400. http://i245.photobucket.com/albums/gg76/gi57/Reloading/PA101989.jpg http://i245.photobucket.com/albums/gg76/gi57/Reloading/PA101990.jpg Slam fires in an AR are almost impossible. If one does occur it will be due to seriously flawed or out of spec ammunition. The round in the pictures did not fire out of battery. If it had, the case head would have ruptured or separated from the body od the case. Looks more like a magnum primer that was fired with no powder charge or bullet in the case.... or perhaps a small pistol primer fired under the same conditions. Notice the extrusion back into the firing pin hole in the bolt face. This usually occurs due to excessive pressure in a normally loaded round, but there is no flattening of the primer cup around the outside adjacent to the primer pocket. The remaining firing pin indentation in the primer appears too deep to be just from chambering the round. I have been using CCI #400 primers for many years with no problems. The nickle plating on this primer looks rougher than what I have ever seen on a CCI primer. Almost looks like it has been bead blasted. Normally their primers are very smooth and shiny. Slam fires as you mention are ALMOST IMPOSSIBLE, but can happen in any floating firing pin firearm. If one occurs it is a pretty good chance it was a sensitive primer and the light hit from the firing pin bumping it as the bolt closed set it off. This is evident by the spot the firing pin hit being extruded into the firing pin hole of the bolt, without the hammer there to support the firing pin the primer pushed out when the round fired. As you say it could have been an excessive pressure round, but that the primer is still rounded on the sides which shows a mildly loaded round. This can only be explained as the round was fired by the firing pin striking the primer without the hammer hitting the pin. If you have been using CCI400's for years you should take a look at one that has been fired out of a rifle with a rough bolt face, it takes the same pattern as the bolt face has. A rough bolt face that has been bead or sand blasted prior to parkerizing will cause a primer to have a "bead blasted" look to it when it gets pushed into it at 50,000 psi. I can assure you, this case is from a round that slam fired. |
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Quoted:
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Slam fires do happen. I had it happen with a CCI400. http://i245.photobucket.com/albums/gg76/gi57/Reloading/PA101989.jpg http://i245.photobucket.com/albums/gg76/gi57/Reloading/PA101990.jpg Slam fires in an AR are almost impossible. If one does occur it will be due to seriously flawed or out of spec ammunition. The round in the pictures did not fire out of battery. If it had, the case head would have ruptured or separated from the body od the case. Looks more like a magnum primer that was fired with no powder charge or bullet in the case.... or perhaps a small pistol primer fired under the same conditions. Notice the extrusion back into the firing pin hole in the bolt face. This usually occurs due to excessive pressure in a normally loaded round, but there is no flattening of the primer cup around the outside adjacent to the primer pocket. The remaining firing pin indentation in the primer appears too deep to be just from chambering the round. I have been using CCI #400 primers for many years with no problems. The nickle plating on this primer looks rougher than what I have ever seen on a CCI primer. Almost looks like it has been bead blasted. Normally their primers are very smooth and shiny. ALL this ^^^^^^^ and 100% 
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I think the thread title is presumptuous.....sounds more like a double to me.
My #1 suspect would be the FCG and namely, as suggested above, the disconnector. IIRC, Plumb Crazy uses a proprietary FCG. I would be very tempted to pull that stuff out and replace it with a good mil spec FCG. |
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I would remove and inspect the FCG first. BE SURE TO FUNCTION CHECK The reload could have had an improperly seated soft primer. Broken gas ring after 40 rounds? Just replace with standard gas rings. I did not have good results with the one piece gas ring. This. If you shoot enough you will see slam fires. I have had a few with even the best ammo money can buy. Always close ur. Bolt in a safe direction. And when you put ur bolt in turn it at the same time you push. New gas rings are nortorious for this.
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Quoted:
I think a primer wasn't seated all the way. I don't think you understand completely what a slam fire is. It doesn't have to do with the hammer on the fcg, it has to do with the fact that the firing pin is free-floating in the bolt and can make contact with the primer if the bolt is closed. Load a round into your chamber letting the bcg close with the bolt release or fire a round with more in the mag. Clear the weapon and look at your primer. Should see a light dimple on the primer. Reasons: 1. You were using hand loads. Primer may have come loose. 2. Out of that many rounds I would expect it to happen more than once. + this.. believe it was a high primer too.. if the FCG was that out of spec it would have happened again... be thankful either way it didn't blow up in your face, crack your bolt and expand both your receivers while destroying your mag. That said, you do need to inspect and do a full function test of the weapon... |
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