How Select Fire Mechanisms Work in Firearms

hello and welcome this is mouse Connor and in this video I'm going to cover how select fire mechanisms work in firearms this video is going to showcase a few examples of select fire mechanisms and closed bolt hammer fired actions I will point out this is by no means the only type of action to have select fire functionality but as I have already shown how select fire mechanisms work and open bolt firearms I would refer you to the video on open bolt actions for further information closed bolt striker fired actions can also have select fire modes but unfortunately I'm limited by the examples available to me and the program I use for these demonstrations and hammer fired actions with select fire mechanisms are by far more common and the first example we're going to take a look at is the ak-47 and/or start off by identifying some of the major components that you may be familiar with have you seen my hammer fired video so starting off we have the hammer itself here we have the trigger with the sear attached so the sear is in contact with the hammer due to this surface right here and when we pull the trigger and the semi-automatic mode that Sierra's going to pivot down and away from its contact with the hammer letting it go so we're seeing a repeat of the same fundamentals we've seen with other hammer fired actions but just like with other hammer fired actions that are semi-automatic there has to be some mechanism that's going to hold the hammer in place until the bolt comes back into batteries so as the bolt comes back to the rear we need some mechanism to hold the hammer in place while the bolt is coming forward and keep it held back until the bolt is fully forward into battery and to do this we have this hook here that is part of the trigger group this hook ensures that as long as we have the trigger held in in the semi-automatic mode that we cannot drop the hammer again once the bolt comes fully forward and comes into battery if we are to let out the trigger eventually due to its attachment with the trigger this hook will also pivot away releasing the hammer but at the moment that it releases the hammer the seer is in place to catch it and prevents it from coming forward now the trigger is reset the hammer is held by the seer so if we were to pull the trigger again the hammer would fall forward this is it's normal semi-automatic function and this hook is going to keep that hammer held so that we have that to my hang automatic functionality and do not drop the hammer until the bolt is fully forward into battery and the trigger is reset now you might be wondering what is preventing me from letting out the trigger before the both is fully in battery well there's another backup mechanism and this mechanism is part of how the fully automatic function works as well and it is this lever here and if we bring the x-ray out a little bit we can see but this lever is going to cam as the bolt comes forward now what is important about this is without it camming this lever will block the hammer from being able to come forward so it's these two mechanisms this mechanism here prevents the book the hammer from coming forward until the bolt is fully in battery once the bolt is fully in battery like so this block is no longer in the way of the hammer and now we can let out the trigger and let it reset or this year to drop the hammer again when we pull the trigger again so how does this differ in the fully automatic mode well obviously we don't want this hook to hold back the hammer until the trigger is reset before we can shoot again we want the firearm to continue to cycle and fire off more rounds as long as we have the trigger held in so our selector switch is going to allow us to do that so if we bring out the x-ray a little bit we can see the selector switch here which is this big lever and it has two functions it can either put the firearm on fully automatic mode or it can put it on safe for now we're just going to look at it in fully automatic mode so as we flip this lever into that setting we're going to push this block in the way of this hook so we can see here this is pivoted into contact with the back end of the hook and if we bring the x-ray back around so you can see but we're not obstructing the function of the trigger so if we were to pull the trigger now we can see that with the trigger held in this hook is no longer going to pivot with the trigger it's being held down by the selector switch so when the hammer comes forward and strikes the firing pin the bull is going to push the hammer back but no longer is this hook going to hold on to it it is not pivoting up into a position where it can contact it so now the only mechanism we have acting upon the hammer is this lever here so once it cams into this position blocking the hammer the hammer will be held in place the bullet comes forward into battery the lever is gonna cam back out of the way and once it cams out of the way the hammer is just going to drop forward again now we don't see that happening here because we are letting out the trigger but if I were to continue to hold in the trigger like so we're gonna continue to cycle so every time that block releases the hammer the action cycles one more time and that is more or less how to select fire functionality and the ak-47 works all we need is this block to come in prevent the hook from grabbing onto the hammer until the trigger is reset without that hook grabbing onto the hammer we don't need to have the trigger reset for the hammer to be able to drop again so it will drop every time this lever cams when the bolt goes into battery so that's how that functions and just to show what happens when the lever goes into safe mode let's go ahead and do that and here we can see that it pivots further in so the fully automatic mode is in between semi-automatic mode and safe if we flip the lever fully tinta to the safe position what happens is the block pivots in and it will block not only the hook but also the trigger itself so if we try and pull the trigger the trigger will not pivot and the sear will not let go of the hammer so that is how the selector switch on the ak-47 works and as the dual functionality of allowing for fully automatic fire as well as putting the firearm into safe the next couple examples we're going to take a look at our variance of the ar-15 platform the first of which is the m16a1 which only has semi-automatic and fully automatic firing modes we're going to start off by taking a look at the semi-automatic mode so we can see how that functions and see how it compares to the functionality of the fully automatic mode the selector switch is right here and currently it is in the semi-automatic mode so as we pull the trigger the trigger is going to pivot and the sear which is here is going to break as contact with the hammer here once that happens the hammer is going to fall forward and as the bolt pushes the hammer back it's going to contact this hook very reminiscent of how the ak-47 works the hook is going to hold the hammer back until the trigger is released at which point the seer comes back into contact with the hammer preventing it from falling fully forward and for the fully automatic mode the selector switch is going to achieve one of the same functions that the selector switch on the ak-47 did and that is holding down this hook and preventing it from grabbing on to our hammer and it does this as it pivots by physically blocking that piece with this part in the middle comes into contact with that central piece as we can see there and prevents it from pivoting upward being able to grab on to our hook what the selector switch does another thing let's take a look at that again so in the semi-automatic mode it is blocking this part here which is a part we haven't yet considered there's a reason we haven't considered it because in the semi-automatic mode it serves no purpose but in fully automatic mode it is very important so let's go ahead and take a look at what it does so as you can see there I'll pause it this piece is now able to pivot because the selector switch is no longer blocking it and we can see that it has a spring acting upon it but currently it is not moving under that spring tension and the reason for that is the bolt here is currently keeping it held forward but once the hammer comes forward and the bolt starts to recoil it's going to allow this piece to move and as the hammer comes back to contact that piece and then the piece is going to pivot up and fall in the space with this notch and once the hammer tries to come back up this piece is going to grab the hammer and prevent it from falling forward until the bolt comes fully and the battery and we'll see that happen as that part of the bolt that kept this B's forward comes into contact with it's going to push it forward again breaking its contact with the hammer at which point the hammer can then drop forward again but in this instance we haven't held the trigger in though the trigger is going to reset and the sear is going to stop the hammer from being able to move forward but if we were to hold the trigger in we can see that interaction every time the bolt comes fully forward it's going to push forward on that locking pleat piece allowing the hammer to drop forward again that's not until we let he trigger out that the seer will grab ahold of the hammer and prevent it from coming forward or continuing to come forward that's more or less how the select-fire function works on the m16a1 so with the selector switch set on to semi-automatic mode it I think I have a little bit of an issue because I need to reload and we'll speed that up there we go now with the bolt forward if we were to switch the selector switch over we block this piece preventing it from moving and when we pulled the trigger this piece will no longer move because it's being held by the selector switch let's slow that down so we can see a little bit better and now it's going to be the hook that acts upon the hammer instead the last exam we're going to take a look at as the m4 carbine which is going to function similarly to that of the m16a1 but one extra bit of functionality is going to change up its function quite a bit and that is the addition of a burst fire mode so just like with the m16a1 we have the trigger here the sear with an with its contact with the hammer and I would say a hook but in this case there's actually two hooks and this is to facilitate the burst fire mode so with the selector switch in the semi-automatic mode currently the selector switch is holding in the innermost or rightmost hook preventing it from moving but the leftmost or outermost hook as we are looking from this side will move during the cycling of the action so as we pull the trigger we'll see that outermost hook move it forward and it will interact with the hammer just like what we saw with the m16 and it's not until we let the tricker back out and it resets and the seer grabs ahold of the hammer that another trigger pull will allow the hammer to drop forward again so very similar there but we do have this extra hook here and we also have the locking piece like before now the fully automatic mode works pretty much exactly the same as what we've seen before so let's go ahead and take a look at that first so if I switch that over to fully automatic mode see that the selector switch is now holding in both hooks preventing them from pivoting and the locking piece is free to move so as we hold on the trigger here we'll see the same overall functionality that we saw with the m16 so nothing really has changed there when we select the burst fire mode what is going to happen is that now rather than holding in the rightmost or innermost hook and preventing it from moving we're going to hold down the leftmost or outermost hook and preventing it from moving so we're not going to have our semi-automatic functionality like what he had before instead it's going to be this hook that we can see in the front that is going to move now in my tests of this firearm in the program I have tried pausing the animation so that I can go through it step-by-step but unfortunately when I do that for whatever reason the program glitches out and then it just stops working at all so instead what I'm gonna do is I'm going to slow it down as slow as I can and we're just going to have to keep our eye on what happens now the main difference with this hook is its interaction via a secondary hook with this ratcheting cog here so we're going to have to pay close attention to this piece and what happens as we hold in the trigger now we're going to fire off three shots with each trigger pole so as I press the trigger we're gonna have shot number one shot number two and we can see that those shots are happening more or less the way they would if this was in fully auto mode but you might have noticed there with the last shot that hook came forward and grabbed a hammer it didn't do it with any other shot so if we watch that again well no hooks not coming forward hooks not coming forward but with a last shot the hook comes forward and this occurs because of this cog and you'll note that the cuts in the COG are actually unevenly distributed so you have shallow cut shallow cut deep cut so if you pay attention to the hook and how it sinks into those cuts first shot we have the shallow cut second shut shallow cut bird shot it falls into the deep cut and then the hook comes in it's a more or less what happens is as the hammer comes forward this spring is going to release its tension driving the hammer for it and when it releases that tension it's going to stop squeezing this inner ring here and we can see inside that as a spring of its own what happens is the cog were freewheel when the spring on the outside of it lets it go and when it free wheels it will not travel with the hammer but as the hammer starts to come back down this spring is going to squeeze it again and then the two will move together so let's watch it an interaction but also as it occurs watch what the hook does to the COG as well so pay close attention to the cog and zone out pretty much everything else so here as the hammer comes forward and the cog is freewheeling the hook is literally pulling down on the cog and making it so that it ratchets around to the next not so if we watch that one more time you'll see once the cog starts to freewheel its gonna try and go with the hammer but the hook is going to prevent it this spins the fog around allowing the hook to continue to go along the cog ratcheting along until we get into that deep cut then the hooks going to come in grab the hammer so this is how it does the three shots and then stops so it's pretty complex in the way it functions and I hope I explained it well enough for you to understand it and I really do apologize that I can't slowly go through the motions but that is more or less how it works it's just a ratcheting action as the spring here releases attention it allows the fog to freewheel the hook prevents it from moving and more or less pulls it down so that when the hammer comes back and the spring squeezes the cog again the hammer and the COG will move together so as the hammer is coming back it's going to ratchet that cog along to the next cut and it continues to do this so until that hook finally falls into the deep cut which is going to cause the hook to grab the hammer in any case that's going to wrap up my look at the select-fire functionality and firearms I hope you guys have enjoyed the video and learn something about how this works this is a mouse Connor signing out

Channel: MouseGunner

Views: 88,728

Rating: 4.8725214 out of 5

Keywords: firearms, full auto, full-auto, m16, m4, ak47

Id: PaFHuqBmDmk

Length: 20min 47sec (1247 seconds)

Published: Fri Feb 19 2016