First Time Out With My First AR-15 Build....

[goodlookin1]

And I almost got kicked out! Well, not really because the range marshal was cool, but I did have to put the gun away for the day. I fired Remington Varmint 45gr (20 rounds) and the rest was PMC 55gr (about 50 rounds). I have a DPMS LPK and a CMMG M4 16" upper. I was simply sighting in my Bushnell Trophy red dot scope when I had a much dreaded double fire. I immediately knew something was wrong, so I put it in safe mode and took the clip out. With the marshal coming over and other onlookers curious, I began to inspect the gun....doing so with great concern (wanted to look innocent!). Anyways, apparently the bolt and carrier group were not lubricated enough and the firing pin was getting jammed up in the bolt, so when the carrier would snap back into place, it caused the weapon to discharge a second time automatically. Fortunately, it only discharged one more and not the rest of the clip. However, I looked at the primer on the following chambered round, and it had been slightly dented in by the firing pin, meaning the firing pin had not completely retreated from the bolt face when it sprung forward to rechamber. Then I talked to my friend who was with me (who, by the way, was fresh out of a tour in Afghanistan) and he told me that AR15's/M16's/M4's are supposed to slightly dent in the primer upon chambering the next shot. I respect his expertise in the matter, but highly doubted his assertion. It just doesnt seem right. When all is functioning properly, why on earth should the firing pin dent the primer of the next chambered round prior to pulling the trigger? Doesnt seem like that should happen, nor have any purpose in a Semi-Auto weapon.

Any thoughts? The last thing I need is to have an ATF agent out at my range and see this happen.......I have a baby on the way, I cant go to jail!

[THT]

The firing pin moves freely and will dimple primers when a round is chambered. It's normal. I've never experienced one but in extreme cases, it can cause a slamfire which is an unintended discharge due to the FP hitting the primer too hard (this is without the hammer hitting the FP), a soft primer, or a combination of the two.

[aplinker]

I have a hard time buying that as to why you got doubling.

You need to break down your FCG and check that everything (pay special attention to spring orientation and the oddness of the disconnector spring).

[Hunter4life1990]

both ar-15/m-16 variants and sks variants have free floating firing pins and only in extreme cases cause slam firing.i agree with ucla on looking to the fire control group.do a function check to make sure everything is in working order.

[fusionstar]

Could we see a photo of the case in question?
Was it the PMC or Remington?

[nicoroshi]

I agree with Uclaplinker.
Check that disconnector spring. If it's in upside down the disconnector may not hold the hammer back on cycling causing a FA situation (large side down).
Can't hurt to check the firing pin channel also.
The firing pin (as stated earlier) is free floating so will put a small (read very slight) dimple in the primer of the next round chambered during cycle. This should not be enough to set it off though.
AKs will do the same thing as they also have a free floating firing pin.

[Noobert]

yeah, checking disconnecter is your best bet

[goodlookin1]

Thanks for the replys guys.

Here is a pic of the chambered (unfired) case right after the 2 round burst incident:




I am going to give it a good cleaning and have my local Black Rifle shop do a good inspection on my install job of the LPK. I followed the instructions online word for word (http://www.ar15.com/content/guides/assembly/lower/) and the rifle functioned properly for a good 50-60 rounds. I do have to say that the PMC was running very dirty and hot in my gun and that it seems at least feasible that this was the culprit that led to my bolt/fp getting jammed up. The bolt was barely sliding back and forth in the carrier group and was practically dry (I oiled it well last night).

Thanks again.

[theneko]

The PMC that I have run in my ARs has always been really dirty too. You may want to try something else if you want cleaner ammo.

[ERdept]

Somwhat related. Had four and five in a row fire from my self modded 10/22.

I voluntarily stopped, but the range guy said I'd better pack it up and shoot something else. Let me stay there the rest of the day.

[aplinker]

looks pretty normal to me.

Thanks for the replys guys.

Here is a pic of the chambered (unfired) case right after the 2 round burst incident:




I am going to give it a good cleaning and have my local Black Rifle shop do a good inspection on my install job of the LPK. I followed the instructions online word for word (http://www.ar15.com/content/guides/assembly/lower/) and the rifle functioned properly for a good 50-60 rounds. I do have to say that the PMC was running very dirty and hot in my gun and that it seems at least feasible that this was the culprit that led to my bolt/fp getting jammed up. The bolt was barely sliding back and forth in the carrier group and was practically dry (I oiled it well last night).

Thanks again.

[DanHuuN]

Honestly I think you need to clean the BCG and lubricate it! Not too sure about slight dents in chambering a round, as I never noticed it, that is something I'll check tomorrow...

Sorry to be the ******* to say it, but lets refer to them as magazines! Just a pet peeve of mine but who cares anyways!

Best of luck with figuring out the problem! I hope we get to see some feedback once you find out what happened

[Josh3239]

It is called a free floating firing pin. When the bolt slams closed the firing pin comes forward with it and does leave a small imprint on the primer. Most AR15 users don't experience slamfires so I'd say it is pretty safe. If you want to be sure just use ammo with harder primers.

[goodlookin1]

It is called a free floating firing pin. When the bolt slams closed the firing pin comes forward with it and does leave a small imprint on the primer. Most AR15 users don't experience slamfires so I'd say it is pretty safe. If you want to be sure just use ammo with harder primers.

LOL. Good one.

I'll be the first to admit that I'm a n00b at this stuff. Still learning.

But good news! I think I found the REAL culprit! I was completely cleaning out the gun today and gave it a good healthy dose of lube, and noticed that the trigger was getting extremely hard to pull. It was almost like it was getting caught on something before it would release the hammer. Then I found the source of the problem.....the trigger pin had partially come out of the LR! It came out enough to where it was not sitting in the other side of the lower receiver at all, yet still holding the trigger in place because of the pressure from the springs. But however it was placed inside, it was just slightly off making it so that it was catching on something while pulling the trigger. After pounding it back in, all was well. I am sure now that this was the main contributing factor in my double fire. Not sure why I didnt notice that when it first happened.

So now that I know this, I have a second question: How tight should the trigger pin and hammer pin fit into the lower receiver? I can move it back and forth with my fingernail without too much effort, so I am thinking either that the pins are too small, or my lower receiver (Kaiser Defense) was drilled to large. I'll go back to my local shop tomorrow and see if they have some different pins or something.

Thanks for the help guys!

[aplinker]

You've installed something incorrectly.

The trigger pins should not move easily.

The trigger pin itself is held by the hammer spring. The tension of this should keep you from being able to move it.

The hammer is held tightly, as well.

Something is wrong with how you've installed. Either the hammer spring is backwards, the feet aren't on the trigger pins... something.