Let's Talk about Light Primer Strikes... [Archive]

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Razorhunter

07-04-07, 23:27

Ok guys,
Got my first taste of the light primer strikes actually causing a FTF today.
Granted, for years I've known about them, and I always keep an eye on the first round in my mag, which gets chambered numerous times over and over.
However, this was the first time that I've ever actually had a round NOT go off. - FTF. It was a quality round too. (75gr TAP FPD).
SO my questions are as follows:

1. Will a GAS PISTON rifle ALSO cause light firing pin/primer strikes, when chambering/de-chambering rounds repeatedly??? (hell, I say "repeatedly", but my DI Colt causes a light FP strike on the primer after only ONE SINGLE chambering/dechambering of a round. I was just wondering if a gas piston rifle somehow differs from a DI gun with regards to light primer strikes????

2. What do you Mil/LEO guys do when your lives depend on your rifles? Do you keep track of how many strikes a round has taken, and then rotate it out of the lineup, OR do you toss the round, or what???

Can someone explain to me just WHY this happens? Maybe it's late, and I'm tired, but I'm not really grasping what causes a light primer strike?
Is this something that also happens with AR10's, or how about AK's??? ( I assume it's not an AK thing, but thought I'd ask)...
Thanks...

Snake RAH

07-04-07, 23:38

Razorhunter

07-05-07, 06:49

Pat_Rogers

07-05-07, 07:15

Big difference Paul...:eek:

The free floating firing pin will leave an impression on the firing pin, and that is no big deal.
However, what you are doing is breaking the seal between the bullet and the case. Done repeatedly, it is enough to cause problems.
I was working with FAST Co in Bahrain pre 911, and we have over 100 Type 2 Malfunctions with the M9 (something beretta says is impossible) in one iteration.. We figured out that this was guard ammo that they were using up. After repeated chamberings / unloadings the seal was broken sufficiently and the humidity high enough/ long enough where powder contamination was possible.
My SOP is 1 cycle. After that, it is practice ammo.

FYI, while Hornady is a quality maker, they are not without problems. We have see enough failures to fire on that 75 training ammo to make me wary.
Additionally, at a cop class some of their duty pistol ammo (5 rounds) failed to fire at all.

There is a lot of voodoo in ammo, and i don't have access to the sophisticated equipment necessary to do any of it.
So, for my peace of mind, one cycle is all it gets.

AR15barrels

07-05-07, 11:39

Ok, then let me correct myself.
I am NOT talking about light primer strikes. I am INDEED inquiring about the striking of the primer during chambering/dechambering...
Please excuse the incorrect terminology...

Piston operated AR's currently available all retain the same floating firing pin of their DI brothers so you would still get the dimple from chambering.

Armalite has added a spring to the firing pin on the AR-10 as the pin is heavier and could cause a primer ignition with soft primers.

Also note that there are harder primers available from CCI to reduce the effects of chambering with a floating firing pin.

If you look closely at the design of the AR-15, it MAY be possible to get one to run (uncontrolled) full auto simply by increasing the mass of the firing pin.
Perhaps a tungsten firing pin would do this.
That's why the pin is kept to a pretty light weight.

jmart

07-05-07, 14:50

Light primer strikes (not the marking of the primer from chambering) can be caused by:

1) blunted firing pin or firing pin that falls below the minimum measurement on a firing pin protrusion gauge
2) REALLY excessive headspace (another clue of excessive headspace would be wandering groups)
3) hard primer
4) deep seated primer
5) weak or broken hammer spring
6) improperly assembled hammer spring

I've only had one gun with light primer strikes, and it was a M1 carbine with excessive headspace. I've shot a good amount of rounds through my AK clone, AR10, and AR15s, and have not experienced light primer strike.

Actually a primer seated high can lead to this. For the priming compound to reliably detonate from the firing pin strike, the primer has to be seated firmly against the base of the primer pocket. If not seated against the base (i.e., "high"), the primer will protrude from the casehead and a portion of the firing pin's impact energy is wasted in seating the primer the rest of the way. You want that primer fully seated so all of the energy from the pin strike is transferred to the primer causing the compound to detonate.

Another fault could be a crushed primer where the compound cracks underneath the anvil. This is caused by applying too much force during seating (or trying to prime crimped cases without first swaging/reaming away the crimp), crushing the primer compound. Many reloaders prefer a hand held priming tool for this reason, it allows them to feel the primer seat in the pocket. A press mounted tool, especially one that provides a lot of mechanical advantage, doesn't provide this same degree of feel and a ham fisted operator can crush primers without realizing it. They can still go bang, but if that compound in the primer cup cracks, it's more prone to flexing during the firing pin strike and not detonating.

Lastly, primer contamination can kill a primer. While they are sealed, if oils or moisture gets into the compound, it can render them duds. Unless you are a reloader, you can't control any of these things, this is all up to the QC standards and production standards of the ammo mfg.

I'm not a professional, so I don't have any protocol on monitoring my number of chambering cycles, but as Pat has pointed out, I have heard of cases where bullet setback occurs from repeated chambering. If neck tension still remains high enough you run the risk of increased pressures from a deep seated bullet. If neck tension decreases you run the risk of incomplete ignition and squib rounds. That's why crimping is so important, to prevent setback. The nose may get a bit deformed, but the round is still safe to fire. If you do get into the habit of recycling these "repeatedely chambered rounds" back to a position lower in the mag, you should be wary of impacting feeding/chambering reliability with a deformed nose/HP.

If you have a set of calipers, I'd try to experiment with a round out of a lot of ammo. Measure the round before you chamber it the first time. Then chamber it, extract it and remeasure. Continue this and see if the overall length decreases. If it does, and if there's no tip deformation, your round is seating deeper into he case. If the tip deforms, you have a round that is either adequately crimped or has enough neck tension to prevent setback. You might want to bury that round into the mag, noting where you loaded it. Then fire away and make note on whether or not the round feeds reliably. If it hangs up you'll know your weapon is sensitive to nose profile and you can't get away with using these rounds for social purposes. Relegate them to range use only.

Or do as Pat suggests and set an arbitrary limit on how many times you'll allow chambering of a round. That's a very safe, effective, conservative approach.

Razorhunter

07-05-07, 15:13

Thank you gentlemen,
Pat your explanation was excellent, as is yours jmart. I appreciate the info, and everyone taking the time out of their day, giving me a chance to learn things such as this...

BTW,
The spring on the AR10 firing pin has me curious, and is very interesting. I wonder how well this spring works on the AR10's, and I wonder if one could be used on the AR15's????
It's not the END of the world, but damn how I would love to end this issue entirely for good...
Thanks guys...

AR15barrels

07-05-07, 16:10

It's not the END of the world, but damn how I would love to end this issue entirely for good...

You have failed to establish that there actually IS an issue, so how can you end it? ;)

UVvis

07-05-07, 16:34

Paul,

I'm a little confused, in your first post, were you were talking about a failure to fire, then we go on to the little dimple in regards to chambering and chambering. For my clarification, when you said, "However, this was the first time that I've ever actually had a round NOT go off. - FTF. It was a quality round too. (75gr TAP FPD)." Are you meaning you had never loaded a round, then unloaded it without firing? Or did you have a FTF with an actual light primer strike? Or just a dud?

Also, it is very hard to get a round to go off by chambering. I tried for a while and eventually gave up.

jmart

07-05-07, 17:41

TWR

07-05-07, 19:09

While this has nothing to do with FTF and light strikes, maybe it will drive home the practice of tossing a round that has been chambered a few times.
http://img.photobucket.com/albums/v374/TOM64/000_0627.jpg
The round on the left was chambered several times until it just didn't feel right. When I unloaded it I was very thankful I didn't fire this round.

While this maybe attributed to a bad crimp as the one on the right didn't require much force to set the bullet back, it still tells me that repeatedly chambering a single round is not good. It also told me I need to shoot more.

Razorhunter

07-05-07, 20:25

UVvis,

I believe the discussion pertains to repeated chambering resulting in light strikes that eventually render a primer dead. I can see if enough light primer strikes occur that eventually when you yank on the trigger with the intent to fire off the round, the dimple in the primer could have got deep enough that the energy transferred is insufficient to detonate the primer. In effect, a Type 1 malfunction.

.

This is EXACTLY the case. I am sorry that I was unaware that a "light primer strike" was considered to be something else.
jmart's quote above, is DEAD ON.
Each year, when everyone in the area starts BOOMING off fireworks, I break out my own fireworks (my M4), and I'm able to sneak in a few rounds without "disturbing the peace". However, when I pulled the trigger, the 75gr TAP round did NOT go off. Instead, I got the sound of a dry-fire.
This was due to the fact that this first round in my mag, had been chambered (and re-chambered) a few times in the last few weeks, hence the "FTF".

I feel I DO have an issue here (as does everyone else with a floating firing pin).
I mean, WHY the hell do I want to have to worry about keeping track of how many times a round has been chambered?
I realize many of you are quick to jump up and defend the black rifles shortcomings, (as am I as well!), however, I just personally consider this a shortcoming.
Just because a "shortcoming" can be overcome with careful inspection/observation, does not mean such issue is no longer a "shortcoming".
I love the black rifle as much as ANYONE here, I just hate the fact that my first round is going to FTF on me, just because I chambered/de-chambered it a few times...
I think Pat Rogers has the best/most reliable cure for the situation. NEVER chamber/de-chamber a round more than ONCE...
Again, I love the black rifle as much as anyone here, and I CERTAINLY don't want to start a flame war here...
I appreciate EVERY one of you guys' opinions, and all that you guys have contributed...

Pat_Rogers

07-05-07, 21:38

Paul- take a deep breath:)

This is not a rifle design shortcoming- it is an operator shortcoming.
Strongly suggest before you make anymore statements not supported by fact or incorrect as to cause/ effect you get a clear understanding as to how the system works. Dean Caputo's class is a good place to learn.
The floating firing pin is common in many weapons sytems, including 1911, M1, M14 and so on.
It is not a problem.
I have never observed a primed case cease functioning because it had been chambered multiple times.
I have seen pressure spikes and issues possibly related to powder contamination.
This may be a bad primer, or other issues, but before you continue to make illogical statements you either have proof or at least a working knowledge of the gun.
I have no idea why you continue to load / unload the same round multiple times, but it is a bad practice.
You do not have to count this more than once- anything more has the potential to be a problem.
I strongly hope that when you firse those shots you have a safe backstop and are doing it legally and ethically.

How is that?

Razorhunter

07-05-07, 22:45

Paul- take a deep breath:)

I have never observed a primed case cease functioning because it had been chambered multiple times.

Well I have. :eek: Just last night, and about 3 months ago it happed as well. Two totally seperate lots of TAP FPD. Two exact same scenarios.
Maybe I'm not understanding you correctly, but I've known of many people who have had this problem/issue/situation? (for lack of a better term to suit everyone here).
I am not in any way questioning your expertise Mr Rogers, and I never will, but ALL I am saying is that I have had multiple rounds (of QUALITY ammo, from several different milspec M4's), FAIL TO FIRE, after being chambered xx number of times. I would venture to say I've personally had this happen 4-5 times total, in my personal experience. The last two times it has happened, I have saved the 75gr TAP rounds. One of those rounds is sitting here in my peripheral vision now, as I type. The other is floating around here somewhere I think.
I will agree that it can be prevented by taking your own advice above (by making sure NOT to chamber/dechamber a round more than once).

Regardless of what the exact science is behind it, the bottom line is that these continued strikes on the primer by the floating FP, eventually caused the FTF. Am I wrong here? Are you saying these were mere "duds" from the factory, and it was just extreme coincidence that it happened each time, to the round that had been chambered/dechambered multiple times???
I mean no argumentative insult here by any means. Just trying to learn a thing or two.
I thought I had previously learned that repeated chambering of a round in the AR15, can AND WILL eventually cause FTF's...
This is something I THOUGHT I had learned on this forum, but maybe I am badly mistaken..?? I was fairly certain though.
I am not sure what we are debating (are we even debating?).

Pat Rogers wrote: "I strongly hope that when you firse those shots you have a safe backstop "

How about mother EARTH for a backstop?
No idea why you would mention it, :confused: but I would NEVER in my lifetime even CONSIDER shooting illegally, let alone, unsafely. :confused:
It's 100% legal to shoot where said event took place. There are simply a few neighbors (and their horses), up the road that get disturbed by the noise sometimes, so we take it upon ourselves (out of simple courtesy), to limit our shooting to the weekends during daylight hours.
However, I "sneak" a few rounds down range, when the heavy fireworks start sounding off each year.
Now- how is that?

Again, this is not an attempt to question your expertise. More like question my understanding of your expertise...

rhino

07-05-07, 23:04

While this maybe attributed to a bad crimp as the one on the right didn't require much force to set the bullet back, it still tells me that repeatedly chambering a single round is not good. It also told me I need to shoot more.

Crimp is usually not the problem, but instead the hollow point is catching on something as it is being chambered. I went through this with a .45ACP Colt a few years ago and I thought it was an inadequate crimp too.

It's possible every single round of that shape and overall length is getting a little setback each time it chambers, or it might just happen when you cycle it by hand.

Do you feel or hear a little "hitch" when it's going into battery when you cycle the first round by hand?

jmart

07-05-07, 23:06

While this has nothing to do with FTF and light strikes, maybe it will drive home the practice of tossing a round that has been chambered a few times.

The round on the left was chambered several times until it just didn't feel right. When I unloaded it I was very thankful I didn't fire this round.

While this maybe attributed to a bad crimp as the one on the right didn't require much force to set the bullet back, it still tells me that repeatedly chambering a single round is not good. It also told me I need to shoot more.

Reloads or factory? Is that .357 Sig?

TWR

07-05-07, 23:21

Those were factory win in 357 sig, I carry a Glock 32 and whatever the reason it got my attention. It seems to feed pretty smoothly but I have since switched ammo and shoot more often. I used to keep an extra mag loaded with practice ammo, now it's all the same. That round probably got chambered 100 times or more...operator error I know.

Pat_Rogers

07-06-07, 04:29

Paul- i am fortunate in that i get to see a lot of ammo of different makers go downrange every year.
I see a great numbers of Type 1 Malfunctions. Most FTF are operator indiced (failure to chamber etc) but also see a great number of rounds that FTF. This includes Hornady, M855, WW and so foth.
They make ammo by the millions- things happen. I stated this in my first post, specifically about Hornady.

Your chambering of a single round may be a red herring. I stated- and will re state- that i have never seen rechambering a round be the sole cause of a primer failure, but can imagine that poor storage methods, WX and so forth could do it.

However, you are blaming it on a free float firing pin, calling it a shortcoming.
It isin't.
You have bad luck, bad juju or bad training. Obfuscation doesn't help:)
Stop rechambering rounds- that is a bad practice.
Report back after you have fired 5-10k rds of your ammunition and advise if you have similar problems.
You may have a bad gun, bad parts, bad cleaning etc.
But learn your gun...

UVvis

07-06-07, 09:50

Paul and Jmart, Thanks for the clarification. I was getting a little lost, and my reading comprehension is down from pushing paper for the last two weeks.

Paul,

How many chamberings are we talking about? I'm thinking that you might have some other issue, maybe bad primers on your ammo, or a damaged firing pin. Have you ever popped a primer that you know of, and can you compare your firing pin to a new or known good pin? Have you tried the duds in a different gun?

twl

07-06-07, 10:25

Does this ammo that you've been using have sealed primers?

Chambering a round on a lubed bolt, and then leaving it in the chamber, or not wiping it off may allow lube to penetrate the primer pocket(over a time period) and deactivate the round.

It may have nothing whatever to do with the firing pin.

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. Not that I'd recommend either of those things personally, but you can get them with the HK if for some reason you'd want things like that.

The spring loaded firing pin doesn't do a thing for you, but it sets worried people's minds at ease.

Also, I fully concur with not repeatedly re-chambering a round.

Heavy Metal

07-10-07, 19:18

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

MASP7

07-10-07, 21:19

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

07-11-07, 10:47

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

07-11-07, 11:10

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... :rolleyes:
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

07-11-07, 18:59

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...:rolleyes:

shark31

07-11-07, 20:51

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

12-07-07, 23:27

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

12-08-07, 01:59

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

12-08-07, 09:01

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

12-09-07, 13:48

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.

http://www.meyergage.com/images/products/class_z_eng_indiv.jpg

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

http://www.meyergage.com/images/products/english_plastic_boxes2.jpg

PALADIN-hgwt

12-09-07, 14:01

xxxxx

turnero

12-09-07, 20:39

Thank You so much for those instructions.

I am now in the process of getting those gauges, .08", .10", .12". As these are fairly expensive, I am having then ground by a machine shop and am considering having them hardened. I sort of have free access to minor works in machining.

As an update to my previous post, I have not yet tested the unit with an H3 buffer and have decided to first check the auto sear timing just to be sure.

Thank you again.