Let's Talk about Light Primer Strikes...

[Heavy Metal]

I agree TWL, this sound like some kind of contamination beyond a humid atmosphere.

[MASP7]

However, if you do want a spring-loaded firing pin, you might look into trying to find one of those $5000 HK 416 uppers that made it into the states. They have a spring loaded firing pin and piston operation too.

HK416's do have a spring loaded firing pin, but it is in conjunction with a hammer actuated firing pin block. (Talk about firing pin safety!)

The floating firing pin is common in many weapons sytems, including 1911, M1, M14 and so on.

Not that it adds anything to the discussion... but, I don't think you can include the 1911 in the free-floating firing pin club.
The 1911 firing pin has a spring.



Somebody need to spend a hour at the range loading a single round in an AR a hundred times to see if it makes a difference...
Who here doesn't have a life???

[shark31]

The first guy in my unit that was killed in OIF1 was killed by an AD later determined to be caused by the "free floating firing pin".

[AR15barrels]

The first guy in my unit that was killed in OIF1 was killed an AD later determined to be caused by the "free floating firing pin".

I'd like to read that report...
I'm of the opinion that there's no such thing as an "accidental discharge", only a "negligent discharge".
Even if there is a weapon/ammo malfunction, that's no excuse for poor muzzle control.
The only way to get injured/killed by a malfunctioning weapon is to be in the bullet's path.

[Pat_Rogers]

MASP7- arrrggghhhhh! You are of course correct. I have only carried a 1911 for a good portion of my adult life, so you would think i was more astute then that.

Note to self- do no post while tired...

[shark31]

I did not witness the event with my own eyes. Lesson learned was to not sling your rifle on you back.

I suppose that the pin bounced so hard when the rifle hit the ground that it struck the primer hard enough for it to discharge.

He is the first casualty listed:
http://www.173rdairborne.com/KIA.htm

[turnero]

Good day everyone,

I get a FTF when I go full auto and this happens on the 2nd round, sometimes third or forth round. A round is chambered and the hammer is down but the round did not fire. Upon inspection the primer has a very slight indentation and my first thought is that the hammer followed. The rifle works fine on semi-auto but has not yet worked properly on full auto since it was built. I have been reading about "bolt bounce" somewhere in this forum but failed to get details that makes it comparable with my situation.

I am hoping to get some inputs here for the mean time since it's still tomorrow that I can go to the range and try an H3 buffer and see if it goes full auto.

[AR15barrels]

I get a FTF when I go full auto and this happens on the 2nd round, sometimes third or forth round. A round is chambered and the hammer is down but the round did not fire. Upon inspection the primer has a very slight indentation and my first thought is that the hammer followed. The rifle works fine on semi-auto but has not yet worked properly on full auto since it was built. I have been reading about "bolt bounce" somewhere in this forum but failed to get details that makes it comparable with my situation.

I am hoping to get some inputs here for the mean time since it's still tomorrow that I can go to the range and try an H3 buffer and see if it goes full auto.

The light dimple on the firing pin is normal in ALL AR's and M16's as the firing pin is floating and taps the primer during chambering.

Hammer down over a live round can be either hammer follow or bolt bounce.

Try the heavier buffer.
It will slow down the cyclic rate and eliminate the bolt bounce if that's your problem.
It can also be sear timing. (releasing the hammer too soon)
Check that with a pin gauge. (I forget what size)

Does the fire control group have all the proper pieces where they belong?

[turnero]

It can also be sear timing. (releasing the hammer too soon)
Check that with a pin gauge. (I forget what size)

Does the fire control group have all the proper pieces where they belong?

How do I check sear timing? And what is a pin gauge?

I'm pretty sure that all the pieces of the fire control group are in proper place.

I'm just asking this questions just in case the H3 buffer would not cure my problem.

Thank you so much for the help.

[AR15barrels]

How do I check sear timing?

Quoted from Quarterbore's DIAS page: http://www.quarterbore.com/nfa/dias.html

Remove any magazine and ammo from the gun.
Set the selector on the full auto position.
Drop the hammer with the trigger (you did check to see the chamber was empty right?)
Now you need your timing gages ( The cheapest is drill shanks at the required dimensions. I use three, one early timing gage .12 dia, one correctly timed gage .10 dia, and one late timed gage .08 dia.)
Secure the trigger in the fired condition (rearward) with wire. Using the charging handle pull the bolt carrier all the way to the rear but do not let it go, slowly lower the carrier towards the front until you have a 1/2" gap left between the carrier and barrel extension.
Insert the early timed gage in between the colt carrier and the barrel extension (not the bolt head) and slowly lower the bolt carrier with the charging handle. If the auto sear releases then your gun is out of time (early) and will most likely give you light primer hits. If not go to step 7.
Slightly retract the charging handle and remove the early gage and insert the late gage. Slowly lower the carrier until the carrier rest on the gage that is between the bolt carrier and the barrel extension. The hammer should have dropped, if it did not the gun is out of time (late) and will most likely either not release the hammer or act sluggish and have a slow cyclic rate. If it dropped go to step 8.
Pull back on the charging handle and recock the gun while removing the late gage. slowly lower the bolt carrier with the "go" or correctly timed gage until the bolt carrier rest on the gage that is against the barrel extension. The hammer might release or might not.
This same system could be used to check the timing of a M-16 or RR AR-15 using a traditional auto sear as well. The key is to set the timing so the hammer falls with the 0.10 diameter gage but not the early gage. Assuming that the hammer was released on this gage but not the early gage the gun is timed.

And what is a pin gauge?

Pin gauges are short round steel pins that are precisely ground to specific diameters.



I have pin gauges from 0.060" up to 0.500" in 0.001" steps.
They generally come in a large sets like this: