AR trigger pin walking; doubling, tripling

[GunnySkox]

Howdy, everyone,

I built a 20" (Would you believe it, like three people came up and expressed their... I don't know that I'd call it than-- ah, gladness that I'd built up a 20 incher, instead of a shorter one. Weird.) AR on a DPMS A-15 lower and a kit purchased from Del-Ton over June, and had my first opportunity to shoot it on Tuesday.

About half way through my second (20 round) magazine of firing rapidly, my AR tripled. I looked around the range to see if anyone was giving me quizzical looks and tried it again: it quadrupled.

At that point, I read my AR the riot act with a complimentary burlap sack of what-for while clearing it and popping the pins to separate the upper and lower.

After a minute or so of fiddling, I found that the trigger pin had waddled its way to the left enough so that it'd come out of its hole on the right side, which made the trigger and disconnector hang noticeably down and to the rear, which I assume gave them only a tenuous grasp of the hammer, leading to my rifle multipling without my consent.

It was easy enough to wiggle the trigger a little and get the pin to go back in its hole, and the gun shot fine for the rest of my time on the range (but for another incident or two of that damned pin walking out), but now I've got to do something about it, so here's some questions:

A) What could've led to this? A pin too small? A hole too big? Anything I can do anything about without just up and replacing the parts?

B) Which companies make reasonably-priced, effective anti-walk pins?

Thanks in advance, y'all,
~GnSx

 

[444]

These are the good ones.

http://cmmginc.secure-mall.com/shop/index.php?shop=1&cat=11

 

[MountainBear]

Had an AR do the same to me in terms of tripling. Fix this before you shoot again. If the pin is walking out, the disconnector is failing and I believe its possible to have an out of battery explosion (i.e. the round is not in the chamber fully when it goes off). I agree with the link above, those have worked well in my buddies AR...

 

[g56]

The trigger pin is retained by the hammer spring, the arm of the hammer spring fits in a notch of the trigger pin, preventing it from moving out of place, that's what those notches in the pins are for. You should be able to look into the lower and easily see if the arm of the hammer spring is in the notch. Those aftermarket retainers are good for old worn out AR's with the holes wallowed out, but totally unnecessary for the average AR owner.

and I believe its possible to have an out of battery explosion

Lemme let you in on a little secret, the firing pin on an AR cannot reach the primer in a cartridge until the bolt is closed and locked, it's impossible.

 

[444]

"totally unnecessary for the average AR owner"

That may be true for the average AR owner, but the average AR doesn't have the pins walk out either.
I have owned over a dozen ARs, still have most of them. I have also been to an AR15 armors class.
ONE of my ARs (an SGW, Olympic) has the hammer pin walk out everytime it was fired prior to me replacing the pin. Either the pin or the receiever or both are out of spec. Why it happens isn't a big deal, the fact that it DOES happen is a big deal. The spring DOESN'T hold it in. The KNS pins do hold it in. Problem solved, end of story.

It isn't doing this guy with the problem any good to make broad, sweeping generalizations when it it obvious that they don't apply to his gun. But, by all means, check the spring to see if it is in the slot. All I am trying to point out is that it is possible to have the hammer pin walk even though the spring IS in the slot.

 

[GunnySkox]

Thanks, y'all.

Once I've got all my school books purchased, I'll snatch up one of those anti-walk sets from CMMG, and get my mom to send me my punch set so I can bop 'em in next time I go to the range.

Cheers!
~GnSx

PS:
"It's impossible.."
Impossibler things have gotten people hurt and killed.

 

[g56]

ONE of my ARs (an SGW, Olympic) has the hammer pin walk out everytime it was fired prior to me replacing the pin.

Yep, sounds like an Olympic...

My broad, sweeping generalization said:
"but totally unnecessary for the average AR owner."

 

[444]

Hey, I gave you credit for that. The average AR pins don't walk but some do. That is all I am saying. I have only had one that ever did it. But, I couldn't get it to stop without some kind of aftermarket pins.
Believe it or not, that Olympic is by far my most expensive AR. That was a "pre-ban" rifle that I bought during the ban. I think I paid like $1100 for it.
It is still the only AR I have equipped with a collapsible stock, so if the mood strikes me I still shoot it quite a bit.

 

[Grump]

Lemme let you in on a little secret, the firing pin on an AR cannot reach the primer in a cartridge until the bolt is closed and locked, it's impossible.

Uh, I think you may be wrong. As the bolt hits the end of its forward travel, the bolt carrier continues a bit more forward and cams the bolt locked. The FP *can* hit the primer at that point before the lockup begins, but it's just a bit hard to get the hammer to hit the FP.

In an AR, there is no mechanical retraction of the FP like you have in M1 Garands and Carbines, and M14 types and Mini-14s.

 

[Bartholomew Roberts]

The FP *can* hit the primer at that point before the lockup begins, but it's just a bit hard to get the hammer to hit the FP.

I don't believe the firing pin can hit the primer before lockup begins because the bolt doesn't telescope back into the bolt carrier (and therefore become short enough for the firing pin to protrude) until after the cam locks the bolt.

 

[Bridger]

Since it's in the same topic, the hammer pin on my service rifle for highpower started to walk out during my last match. I fixed it then and got through the rest of the match no problems, but it makes me nervous.

Should I just get a replacement pin that should have a tighter fit? Is there anything like the KNS pins that are service rifle legal?

 

[MountainBear]

"Lemme let you in on a little secret, the firing pin on an AR cannot reach the primer in a cartridge until the bolt is closed and locked, it's impossible."

I guess I've been wrong before...

 

[rino451]

Lemme let you in on a little secret, the firing pin on an AR cannot reach the primer in a cartridge until the bolt is closed and locked, it's impossible.

Can't tell you how many people don't believe this. Although I didn't know this until I took an AR/M16 armorers course. Slam fire OTOH...

 

[lightweight]

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Since it's in the same topic, the hammer pin on my service rifle for highpower started to walk out during my last match. I fixed it then and got through the rest of the match no problems, but it makes me nervous.

Should I just get a replacement pin that should have a tighter fit? Is there anything like the KNS pins that are service rifle legal?


Spring legs on top of hammer pin and in grooves?

 

[Don't Tread On Me]

I discovered this on my own when I wanted to determine if firing pin contact can be made prior to complete lockup. It cannot (unless something is out of spec).


Simple test. Use one finger to push and hold the firing pin as far forward as it will go. With the other hand, rotate the bolt into the carrier. You'll notice that the pin only protrudes at the very end of the rotation. How much rotation is left? NOT enough so that the rotation is greater than the width of any LUG..which means, the lugs will be behind the barrel extension lugs before the pin can touch the primer.


This is why a long time ago Colt and the BATFE thugs felt that a shrouded firing pin was a bad idea in a semi-auto AR. You see, an AR is techincally safe to "slam fire"...meaning, the absence of a disconnector can allow you to make a fully-automatic rifle that will not stop till the magazine is empty. This is why there is a cutout in the SP1 style carrier and a notch in the hammer - so it "hangs" up - essentially jamming the rifle if there's a disconnector failure (or to prevent the illegal modification by removing it). Thus, preventing more than 1 shot per trigger pull. That's why I love M16 carriers, they do not have designed-to-jam "features"....In a SHTF scenario, it is more important that I get a full-auto outcome due to a disconnector failure than it is to end up with a jammed rifle because in someone's sick-twisted mind...the idea of full-auto fire is far worse than being killed by the home-invader. Remember folks, according to the gubmint - it is better to die with a jammed rifle than it is to have taken out the badguy with a full magazine dump because a tiny piece of metal broke....


Or you can just get an AK

 

[Bridger]

my hammer spring is in the notch on the trigger pin too, made sure of that. The hammer pin though just doesn't seem to have enough holding it from walking out

 

[Bartholomew Roberts]

my hammer spring is in the notch on the trigger pin too, made sure of that. The hammer pin though just doesn't seem to have enough holding it from walking out

It may be time to replace the hammer spring. How old is the rifle? Any issue with light strikes on harder military primers lately?

 

[Bridger]

It's new, no light strikes. I'll have to fiddle with it more on the weekend to make sure it's in the notch though I had done that already. Got a match on sunday and will be practicing on saturday so hopefully it will stay put.