Slamfire issue in AR15

[AKolomiets]

Hey all, I'm having a pesky slamfire issue in my AR15 and I can't seem to get around it. Every round that gets loaded in to the chamber has a light primer strike mark from the firing pin. I thought this might be a cleaning issue, so I stripped the BCG apart and cleaned all the components before assembling it all back together. The firing pin marks are still there, and the occasional slamfires continue just a few rounds in. It doesn't happen every round, but it has been repeating with multiple brands of ammo. Any suggestions? There has to be a good systematic way to tackle this - I just don't know what it is.

My "moving parts" gear list is below
White Oak upper, .223 Wylde
FailZero BCG
JP Enterprises captured spring buffer (rifle length)
Elftmann Tactical match trigger

[1stmar]

Reloads or factory loads?

[AKolomiets]

Both reloads and factory ammo.

[mehavey]

Let's try again....

(1) Are the rounds firing when the bolt first closes....?

-- OR --

(2) ...during the firing sequence after the first round ?


If #1: you may have a "slam" fire
If #2: you are likely doubling due to trigger control or trigger group disconnector issues **



**
Check also: disconnector spring is missing/weak or the hook on the disconnector is worn or the hook on the back of the hammer for the disconnector is worn. Do the following test. Take the upper off the lower. Cock the hammer while the trigger is pulled and held. The hammer is now held back by the disconnector and not the trigger sear. With your other hand grab the hammer and jiggle/pull forward on it. You will most likely see that it can be pulled/slipped off the disconnector. This is what is happening replace worn parts as needed.

[Steve in PA]

The marks on the primer are normal, since the AR has a floating firing pin.

With reloads, a slam fire is usually caused by a primer seated high.

I’ve been shooting and reloading for my AR’s for 20+ years and I’ve never had a slam fire with factory or reloads.

Since you say the slam fires are occurring with both factory and reloads, I’m going to say there is something amiss with your rifle.

And, there is the possibility of #2, described above.

[1stmar]

If slamfire is w reloads could be from not full length sizing.

[10-96]

I don't think it would matter, but there is such a critter called an Enhanced 7.62x39 Firing Pin which was designed for harder primers found on certain steel cased ammo. These tend to protrude a bit further from what I unnerstand. Could you have gotten the wrong FP from somewhere along the way?

Do you have a known performing or other firing pin to test?

[AKolomiets]

Thanks guys. The reloads were full length sized and the primers were seated properly, although I did use bench rest primers and I'm sure those didn't help the problem.
I swapped out the BCG for a spare and the occasional slamfires continued. I'm guessing this narrows it down to the trigger group (unless the buffer could have something to do with it?).

[mehavey]

The bolt/carrier design of the AR makes it very near impossible to truly slamfire from
anything save a broken/stuck firing pin striking the primer in any manner.
High primers ...."maybe," but hardly repeatedly.

Again -- is it firing upon first bolt closure, or doubling during the course of fire therafter ?

[AKolomiets]

It doesn't fire when the bolt first closes. Once I pull the trigger it feels like it fires two shots in quick succession

[mehavey]

Then it's milking the trigger and/or disconnector issue.
Unless you know/trust a good gunsmith, replace the trigger group
-- (relatively) cheap 5 min fix.

https://www.midwayusa.com/s?userSear...temsPerPage=48

pick your poison

[DnPRK]

You are pulling the trigger twice. The second pull is during recoil.

Pull the trigger like you mean it and hold the trigger until the recoil is complete and you have put your sights back on the target. Then release the trigger. It's called follow through.

[Mobuck]

"although I did use bench rest primers and I'm sure those didn't help the problem."

This quite possible BUT

"Once I pull the trigger it feels like it fires two shots in quick succession"

The real issue is you're "bump firing". Trigger management can be an issue for the uninformed. Learn to hold the trigger back until the action cycles-that's how the FCG is designed to work.

[T. O'Heir]

"...could be from not full length sizing..." Nope. If you don't FL resize with a semi-auto the cartridge may or may not chamber at all. Slam fires are caused by improperly loaded ammo. However, in this case, that is not happening.
"...Elftmann Tactical match trigger..." Set at what? It's adjustable from 2.75 to 4 lbs. A 2.75 pound trigger will cause the rifle to go bang if you look at it harshly.
I'd be guessing you're not having a slam fire at all. You're doubling. You're likely failing to follow through on the shot by releasing the trigger too soon and recoil, such as it is, is causing you to pull the trigger again with that high priced trigger set too low.

[Unclenick]

Originally Posted by AKolomiets

It doesn't fire when the bolt first closes. Once I pull the trigger it feels like it fires two shots in quick succession

As already suggested, it's either the disconnector or you have turned yourself into a human bump stock, which is really common. In the latter case, your trigger finger tends to keep its place in space after ignition. Recoil moves the gun back to compress your shoulder while pulling the trigger away from your finger far enough to reset. Then when your shoulder elastically returns to shape it pushes the gun forward against your trigger finger, firing it again. It's quick. To test for this problem, just pull the stock hard against your shoulder while you shoot. If that stops the doubling, this is the problem: too loose hold.

If that doesn't solve the problem, then the disconnector is looking like the villain.