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Thread: Public Service Announcment: check for fire-on-release triggers

  1. #1
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    Public Service Announcment: check for fire-on-release triggers

    Public service announcement: check your FCG for safety and compliance.

    I want to make sure that everyone interested in safety and compliance with existing gun laws, with regard to how their AR15 or AK is configured, is aware of a few things. There are ways to be in violation, or have a potential violation, or at least something that “looks wrong”, without even being aware of it, and at the same time they are safety issues. I’d hate to see anyone get in trouble when they’ve done nothing wrong, but unknown to them there’s something not right in their fire control group, from the factory.

    AR’s first. Most people are aware of the 16” barrel minimum, etc. I want to talk about something hidden in the fire control group (FCG) of many AR’s out there that a person might not notice until the most inopportune time. I have seen it discussed here I believe, but it bears further exposure. I call it a “fire on release” trigger, where, the shooter pulls the trigger, and >bang<. As the shooter releases the trigger, another, unexpected >bang<. Not good! I have seen literally dozens of AR’s come from the factory with this condition, or a condition that is so close to it that at the end of a thousand rounds, as parts get mated, the condition might just appear.

    This is something I explain in detail in every armorer class, because it is obviously a critical safety issue that many manufacturers don’t get and/or aren’t even aware of.

    First, let’s test for it…. and be advised that this applies to standard-format trigger groups but doing this check on anything and everything can’t hurt. Check, check, check that the AR is unloaded. Look into the chamber, and physically give it a feel before doing this—extractors break and leave live rounds in the chamber—you must confirm that the chamber is empty, in good light and by feel. After confirming this, hinge the upper and lower apart, this test is better accomplished with the gun open, anyway.

    Note, with the receivers hinged open or separated, be careful to not let the hammer fall unimpeded against the bolt catch / receiver front wall.

    Cock the hammer. Controlling the hammer with a thumb, pull the trigger until the hammer is released to your thumb; if there is any further trigger travel after this point, “overtravel”, pull the trigger the rest of the way until it stops. Some overtravel would be normal. Let the hammer down, and with the trigger still pulled, re-cock it. It should catch on the disconnector—the most aptly named part in the gun, every semi-auto has one, and it “disconnects” the hammer and sear and keeps the hammer in a cocked position until the shooter releases the trigger to reset the FCG for the next shot.

    So, now, with the trigger still in the fully-pulled position, and the hammer held back by the disonnector, start releasing the trigger forward, as slowly as you can and as “controlled” as you can. Keep your thumb in front of the hammer to protect the bolt catch should the hammer fall. You can actually increase the control of this test by using your thumb to simulate a much weaker hammer spring, in other words, you are taking some of the hammer spring tension off the hammer as you release the trigger, which gives you better control in releasing the trigger.

    Do the test several times and get a feel for it. Look inside and observe the function of the disconnector, and how the front tip of the trigger, which is the “sear” in this case, holds the hammer in the cocked position under normal circumstances. When we pull the trigger, pivoting the actual trigger portion to the rear, the front portion pivots down until it comes out of engagement with the hammer notch—allowing the hammer to fall. Note that as the front of the trigger pivots down, the rear naturally pivots up (unless blocked by the safety selector being in the “safe” position, that’s how the safety works), and the disconnector hook, the bird’s-beak looking part, pivots forward with the trigger. This forward motion of the disconnector puts it in a position to then hook onto the corresponding feature on the hammer, when the gun cycles, and hold the hammer back until we release the trigger. As we release the trigger, the disconnector pivots rearward and the trigger’s sear nose pivots up. The design intent is for the trigger's sear nose to be up far enough to engage the sear notch of the hammer, before the disconnector moves back far enough to come out of engagement with the hammer. When the disconnector releases the hammer, the hammer should fall a short distance with a good solid “clunk” and once again be held back by the sear nose of the trigger: ready for the next shot. I call this the “handoff” from the disconnector to the sear.

    The problem is when, while releasing the trigger forward, the disconnector releases the hammer too soon, before the trigger’s sear nose has pivoted up far enough to catch the hammer. This results in a fire-on-release situation. Patently unsafe and maybe subject to unwanted scrutiny.

    As I’ve said I’ve seen many AR’s with varying degrees of this condition. Some will do it every time. Some are right on the edge and the firer might not notice it without actually trying to induce it, but the fact is, if you can induce it, it will eventually happen. I’ve seen guys where their solution was simply, “I just make sure to release the trigger quickly”. Well, who wants to have to do that. I’m going to tell you how to fix it, but first, how can guns come from the factory this way? That’s a fair question and obviously they shouldn’t, but it can be a matter of tolerance stack up: every part, every dimension has a tolerance and if every part varies within its tolerance in just the right way, sometime unwanted things can happen. Hammer and trigger pin locations and diameters, hammer and trigger profiles, disonnector profile, all have a range within which they are good, but if, say, the hole spread is at max, the disconnector is at minimum, and the top of the trigger’s sear nose is on the low side, etc., well who knows what might happen. Or it might just be some out of spec parts. But AR owners need to know about this and how to fix it..... because many manufacturers don’t know to test for it.

    The standard military armorer approach would be to simply start changing out parts until it stops—this is totally acceptable. But what if you don’t have handfuls of parts to work with, or they all are exactly the same and don’t fix the condition, or you have your FCG worn-in to a really good, smooth pull and you don’t want that to change?

    Take out the trigger and disconnector (remove the hammer first). I won’t cover the “how” on that here, if you don’t already know how, it should be easy to find the procedure. I’ll just say, have your safety glasses on and again, make damned sure it’s unloaded. With the trigger now out of the receiver, put the trigger pin into the trigger with the disconnector in place—the disconnector pivots independently within the trigger and has its own coil spring. Note that the spring is conical so that it’s a press fit into the trigger body, that’s just so it doesn’t get lost. I’ve seen them come from the factory upside down (the high school kid they had assembling them after school discovered they went in easier that way I guess…. nothing against high school kids but the company should be more responsible about training). When they are upside down, they are easily lost, plus the “big” part will tend to do what it was designed to, it will press-fit stick in the hole it lives in, but since the “big” part is up instead of down, it’ll stick the spring in the compressed position—leading to more problems of a similar sort (also sometimes caused by a too-weak disconnector spring—make sure you’ve got the right part in there).

    So—with the trigger and disconnector pinned together now, outside of the receiver, just study the motion of the disconnector within the trigger body. Observe where they make the contact that stops the forward motion of the disconnector “beak”—it’s the underside of the front extension of the disconnector contacting the top deck of the front part of the trigger body, behind the sear tip.

    To allow the disconnector beak to rock further forward, remove a little metal from the underside of the disconnector where it stops off on the trigger top. It’s that simple. The disconnector is heat-treated and pretty hard but you can do it with files.

    But, of course, you can over-do it. Hmm, now how would I know that? Overdone, the disconnector is pivoted so far forward that upon releasing the trigger, the disconnector can’t release the hammer for the hand-off. Now you either take a little off the beak or start with a new disconnector. I’m not sure how hard the disconnector is nor how deep the hardness goes but I really don’t like removing metal from the beak. The underside where we tune is no problem because that’s nothing but an up-down contact surface, not subject to sliding wear or heavy spring loads. If you over-do this my recommendation would be start with a new disconnector. If you will approach it by doing a couple file swipes and then reassemble and try, sneak up on it, you will be good. Or have your buddy who’s good with tools, do it for you.

    I like having it tuned so that when the hand-off occurs, the trigger’s sear nose is up high enough that it is at least 60% engaged with the hammer’s notch. Note that the AR15 standard-format trigger geometry is such that, when the trigger is partially pulled and then released, hammer and trigger pull each other back into 100% engagement. I like that, it makes it all very safe. So likewise, if handoff occurs at 60% engagement, releasing the trigger the rest of the way results in full engagement. My own guns, I fiddle them into darn close to 100% engagements. In a class, when I’m trying to make a student’s fire-on-release condition go away and he’s looking over my shoulder anxious to get back on the line, I go for 60% or better….. I don’t want to go for perfection and then have to un-do some of it. 60% or better, works fine and I believe that the manufacturers who DO watch for this probably have a similar spec.

    There are several little nuances to this that I’ve developed to make it quick and easy but that’s it in a nutshell. Check all your AR’s and don’t have this condition. As I tell the officers in class, imagine you just made the shot that saved the world, you popped the alien queen’s head at 220 yards and now they’re gonna pack up and leave our planet in peace. But in the 1/8 second after you made the shot, two more went off as you released the trigger and they are headed for those two strollers down the block.

    This is info I guess you could say I normally “sell”, but it’s pretty common and I think it’s so important, everyone needs to know this.

    Next—Check your AK’s.

  2. #2
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    Good post. Thanks for taking the time to write it.
    Steve

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    Good info as usual. Thanks for posting.

    Keith

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    Great post, thank you!

    Anyone else think this should be a sticky?

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    Stuck, unless someone deems otherwise. Good post, Ned. Thanks.

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    Great post. Should be pinned.
    I predict future happiness for Americans, if they can prevent the government from wasting the labors of the people under the pretense of taking care of them.
    Thomas Jefferson

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    Quote Originally Posted by Tx_Aggie View Post
    Great post, thank you!

    Anyone else think this should be a sticky?
    I agree.
    I predict future happiness for Americans, if they can prevent the government from wasting the labors of the people under the pretense of taking care of them.
    Thomas Jefferson

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    Guys, it's already pinned.

  9. #9
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    AK's:

    In the select-fire AK, the auto sear is active all the time, unlike the M-16 where putting the selector on "semi" takes the auto sear out of play. This is neither here nor there as we are talking semi-auto-only AK's here, other than to understand that in a semi-auto-only AK, obviously the auto sear is not present.

    When a select-fire AK is set on auto, nothing changes with the auto sear. The only thing that happens is that in the middle selector position, the selector tab gets positioned over the back tail of the disconnector, and the disconnector is taken out of play (in this, the AK and M16 are similar).

    Here's the deal. To my great surprise, I have seen several semi-auto-only AK's over the years that had been put together at the factory with a select-fire disconnector and selector. This means that although these guns are made without a selector detent cut for the "auto" position, if you should put the selector in that position, the selector tab will prevent the disconnector from holding the hammer back. With the trigger pulled and cycling the bolt by hand, the hammer will fall behind the bolt as the bolt comes forward-- as long as the trigger remains pulled. I do not know of actual full-auto fire ever being the result of this; absent the auto sear to delay the hammer's fall, I believe it would always follow too closely to deliver an adequate whack on the firing pin to fire a cartridge. BUT..... if it did, well, would you want that to happen, unexpectedly? And in, shall we say, certain company? It would be an unsafe condition and again, could lead to serious problems. Even if it never fired, to me it just plain "looks bad" and is at the least an inconvenience when you fire a round and can't fire the next one, because the hammer has already fallen on it and not fired it.

    AND, if it did fire a second round, say it was a super-sensitive primer or something, given what we know about bolt bounce, it could be extremely unsafe. Part of the auto sear's job after all is to delay firing the next round until the bolt is closed and locked and any bolt bounce has run its course and stopped. Both the M16 and AK suffered from this in the course of their development, and both have designed-in counter measures-- the dead-blow type buffer in the M16, and on the AKM at least, a rate reducer that I have also seen as having been put there to allow bolt bounce to settle before firing the next round in a burst. This aspect I really don't have the facts on but it sounds viable.

    In short-- I don't see any good reason to have one set up this way. I presume that this configuration passed some sort of approval process to allow import of these-- I've seen it in, I believe, Chinese, Egyptian, and some Eastern European variants-- but myself, I would not rely upon that "it must be legal or they wouldn't have done it that way" for anything. It does not allow auto fire but it allows your gun to become a semi, semi auto-- fire one, rack out a live round, fire one, rack out a live round..... who needs that?! Given the general non-ease with which the AK selector is manipulated, who wants to accidentally put it in this position and have this irritating impediment to getting on with shooting?

    Test for it like this, best accomplished with the dust cover off but if you were testing a fleet of 100 guns you can do it with the dust cover in place. Unload! Remove the magazine. Physically and visually check the chamber with a light. Do not skimp on this. Don't be so much of an expert that you are above safety protocols. Point it in a safe direction while doing this. Cycle the bolt to cock the hammer and put the selector on safe. Try pulling the trigger. Creep the selector down towards "fire" a little at a time, trying the trigger along the way. At some point the hammer will drop. At this point, the earliest point in selector travel at which the hammer will drop, hold the trigger to the rear and cycle the bolt. Watch for the hammer to fall with the bolt moving forward. Test and retest, get the feel for it. If the hammer follows, I say it needs fixin'.

    Fix it thusly. Again, you can find the disassembly instructions elsewhere but this does not necessitate a complete take-down. Remove the selector and identify the downward-projecting tab that, in a select-fire gun, is wide enough to both block the rear of the trigger body from rocking up, that's "safe", but also extends to the left over the disconnector tail, which projects rearward from the disconnector. Actually if you have these features you can see them, and see them work, from the top with the dust cover off. If you have that wider selector tab, you can just grind off the middle part that would act on the disconnector tail, keeping it from pivoting with the trigger. Leave the part that blocks the trigger though! On the disconnector, if it has a tail that extends rearward beyond the trigger body, grind it off. If you have both, do both-- if you have one or the other, I'd still do it.

    If some one can provide pics that'd be great.

    This is not legal advice. For all I know the above setup is completely legal. Even if it is I say get rid of it because there is nothing to gain by it, and there is reliability and safety to lose.

  10. #10
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    Thanks for this post.

    I think I read something about someone designing an AR trigger to do exactly that, and claiming that the trigger is being actuated twice for two shots - first you move it back, then you move it forward. I don't know if it ever entered production but it seemed like a bad idea to me. I think I saw it discussed around when the 3MR came out.

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