how does mechanism of AK-series works?


February 25, 2005, 11:36 AM
G'day everyone,

I've been looking for a while for a good explanation of the mechanism of the AK-47 series, i.e. trigger group and bolt, working, movements, what happens first, etc.

I know how the rifle operates generally, but the details (of triggergroup and bolt) I don't understand: triggers is pulled; gizmo-x goes forward/rotates/releases gizmo y; firing pin goes forward; BANG; now, what happens exactly to the bolt?

Does anyone know a good site that explains in detail how it works? I've already read the operations manual (East-german version) that describes in detail how it works, but somehow, 'the quarter doesn't drop'. Even better: are there any .mpg's around that show (in slowmo) what happens/moves/ when the trigger is pulled.

Am a mechanical engineer by education, but without the real thing in front of me, I can't seem to understand how it works... :confused: The patent drawing also doesn't help much. An animation would be ideal.

Anyone have good suggestions, or .mpgs, or explanations?



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February 25, 2005, 01:16 PM
I saw something like that once ... I think it was on ....(?)

But the details of the animation weren't all that good IMO.

I can tell you this: the AK is a very simple (almost crude) design. There is an internal hammer (under the dust cover) that is cocked by the rearward motion of the bolt, very much like the way a lever action winchester works.

When the trigger is pulled and the hammer released, the hammer strikes the back end of the firing pin which of course runs down a hole the length of the bolt.

As the bullet reaches near the end of the barrel, the hot powder gases are allowed (in sort of a 2-stroke engine fashion) to flow through a port in the top of the barrel into a gas tube, and thereby force a pistion back which operates the bolt. Everything starts all over from there.

February 25, 2005, 01:25 PM
I have a slow motion video of an AK firing in full auto with the dust cover removed on my computer at home... I can send it to you later if you like. You can see the bolt carrier and trigger group cycling.

The AK uses a rotating bolt, btw... as the gas piston is impacted by gas and moves backward, a notch in the carrier rotates the bolt to unlock it before pulling it back. Process is reversed as a new round is chambered.

February 25, 2005, 01:37 PM

Thanks for the reply, but that's what I more or less know; however, I'm trying to get in the nitty-gritty of it: when the trigger is pulled, HOW does it release the hammer (can't understand why I can't understand it; there are only 2-3 moving parts in there :banghead:). The rotating bolt bit is another thing I don't get; the gasses flow back through the 'gas tube' (term?) and pushes the bolt back, which has to rotate; but when I look at the lugs, again, it doesn't make sense.... Now, IF I'd had the thing in front of me I'd simply take it apart and analyze/play with it, but alas...

The trigger group is SO simple, so few parts, but, how does it work :banghead: ..... I'm sure that the patent info on the mechanism says it all, but my Russian isn't good enough yet. Plus there's that bit on a 'designer formula' that I'm interested in. Anyone knows what I mean?

ttbadboy, I think I know the video (from a German website: or one of its links?), showing a man holding the AK firing to the right (with a lot of ground/rubble spluttering back :-). It nicely shows the cycling of the bolt carrier, but not the working of the triggergroup nor what happens inside the bolt carrier.

On my computer, I have a Flash animation of the Browning mechanism (it's a screensaver), which nicely shows how things move/operate with respect to eachother. I'd hoped something like that existed for the AK-mechanism...

Short: the trigger is pulled backwards; the 'top' of the trigger (on the other side of the trigger-pin) the goes forward. BUT, how can this RELEASE the hammer. Plus, there's an extra 'gadget' on the top of the trigger, it has a function in semi- and auto-fire selection, but I don't get how it gets actuated by the fire selection lever.

But you're right, when looking at pictures of the AK trigger group, it's 'crude'. So few parts in it, yet it works....

In the mean time, I'll have another look on, but last time I visited, couldn't find anything.

Anyways, thanks for the replies so far.


AZ Jeff
February 25, 2005, 01:54 PM
Peter, if you are a mechanical engr. student, then just looking at cross sectional diagrams of the AK should allow you to infer how the trigger group operates.

Try finding one of the following books, and it will show you the operating details of the AK series:

Small Arms of the World by Smith and Ezell
The AK-47, by Ezell

February 25, 2005, 03:02 PM
4 parts to a trigger group. trigger, hammer, disconect and sear. the part thats puzzeling you is the sear, kind of like 2 hooks that when the trigger is pulled one hook (on the trigger)is lifted off the other ( on the hammer) and the hammer is under spring tension releases and moves forward striking the fireing pin. the disconect is another hook system normaly on the back of the hammer that catches the hammer after the cycleing has pushed it back to cocked postion. if that wasnt there the rifle would fire full auto. (at least for a few rounds untill a jam) I am not sure on full autos to say how the select fire works other than it delays the hammer just long enough for the action to lock.

on the picture hammer is left trigger is center and disconect is right. there are hooks on the trigger that matches hooks on the hammer. the disconect releases control back to the trigger after the trigger is released to a reset point.

I know it isnt a movie but.

February 25, 2005, 03:36 PM
I am not sure on full autos to say how the select fire works other than it delays the hammer just long enough for the action to lock.

Yeah, there's a little diihickey in front of the hammer on the FA variants that rests on that flat part towards the bottom, locking it in place. When the carrier comes forward, it trips the diihickey which releases the hammer.

(Any chance you can look at a semi copy to see it first person Peter? Where are you?)

February 25, 2005, 04:41 PM
Actually, if the hammer weren't caught and held to the rear during cycling, the rifle wouldn't fire again; the hammer would ride the bolt forward and the hammer would already be down when the bolt closed on the next round. (That's why converting a closed-bolt semiauto to fire full-auto is far, far more difficult than the Bradyites portray it.)

As far as how the bolt rotates, the bolt is more or less cylindrical and is completely surrounded by the bolt carrier. It would be free to spin inside the carrier except for a little spur that fits into an angled slot. As the bolt carrier moves straight to the rear, the angled slot and spur conspire to rotate the bolt about a quarter turn to unlock it; the bolt then moves straight to the rear with the bolt carrier.

February 25, 2005, 04:52 PM
Yeah, there's a little diihickey in front of the hammer on the FA variants that rests on that flat part towards the bottom, locking it in place. When the carrier comes forward, it trips the diihickey which releases the hammer. doohickey :) Here's the long explanation:
Semi-auto: The trigger is pulled. This rotates the sear which is the part that holds the hammer in the cocked position. The hammer lets go under spring pressure, slamming into the firing pin. The cartridge fires. The gas from the cartridge goes down the barrel, then enters the gas port (a hole in the top of the barrel). It goes back down the gas tube and pushes the gas piston (long horizontal rod attached to the bolt carrier). The whole bolt carrier assembly (bolt,carrier and gas piston which are all attached) goes backward,retarded by the spring. The bolt unlocks from the receiver (it rotates in to lock,and out to unlock,with a screw-like motion,executing about 1/2 of a rotation in the process). As the carrier goes back, it strikes the fallen hammer and pushes it back. But... the sear that once held the hammer is not in place to catch it-your trigger finger is still holding the sear down via the trigger. So the hammer catches on another piece that acts whenever the sear is depressed-the disconnector. This disconnector is like a hook that catches the hammer in semi-automatic fire. Meanwhile the bolt slams home. Your finger releases the trigger. The sear engages, and the disconnector (remember,in semi-auto fire whenthe sear is engaged, the disconnector is not and vice versa) releases the hammer. The sear then "catches" the hammer on it's normal hook. The weapon is now cocked and ready to fire again.
Full auto: same as above with the following exception- as the bolt slams home it hits still another piece-the autosear. The autosear is engaged by using the selector lever on the outside. When disengaged, it doesn't contact anything. When engaged, it's function is to rotate the disconnector away from the hammer without rotating the sear (which is only affected by the trigger), releasing the hammer. The autosear is tripped by the forward movement of the bolt carrier,at a point pre-determined by the geometry of the carrier and the autosear. So, with the autosear pulling the disconnector away from the hammer, and the sear depressed by the trigger and unable to hold the hammer, the hammer goes forward firing another round until the trigger is released and the sear can catch the hammer again.

Removing the disconnector itself will not always cause full auto fire. The hammer is usually faster than the bolt closing. If so, lacking a disconnector, it just hits the unclosed bolt (not the firing pin) and rides it forward losing energy to the bolt. Sometimes it still has enough to cause the firing pin to fire the cartridge,sometimes not. That's called a slam fire.

February 25, 2005, 05:36 PM
Poodleshooters explantion was good, here's an animation that may make it clearer. Hope this works!

February 25, 2005, 05:39 PM
Great animation! :cool:

February 25, 2005, 06:27 PM
That's a great animation.

Here's a film of an AK firing with the dust cover removed:

It's about the 4th one down.

February 25, 2005, 06:35 PM
In that video (with the dust cover off), the big piece of metal you see moving back and forth is the bolt carrier, which the gas piston is attached directly to. (You can see the piston rod as the action cycles.) The bolt is carried inside the bolt carrier, toward the bottom (in line with the barrel).

Harry Tuttle
February 26, 2005, 10:01 AM
Peter needs a Kalashnikov

not owning one is a sin for any mechanical engineer

heres valeri Shilin's animation of the action

February 26, 2005, 11:02 PM
Peter, try the website, they have some close, clear pictures of the internals and parts. The animation is good, but if you haven't seen the parts up close, still may not answer all your questions.

March 3, 2005, 11:11 AM
Thanks for the replies, everyone!

Things are starting to make sense, and that animation is BEAUTIFUL...

Kaylee, won't be able to look at one, not even the semi-auto versione. Over here (Netherlands), even toy-guns that only LOOK like real guns are classified as firearms and thus illegal.

Harry Tuttle: LMAO! Agree with you, but it'll have to wait until I work/live in USA. However: every mech.engr. should also have a COLT SAA. plus a semi-auto (Browning-type/Glock).

The more I learn about this rifle (esp. the Dragunov), the better I start to like Mikhail Timofeevitsch. BTW, a friend of mine (see used to design gundrills for Kalashnikov rifles; he was (rightly) proud of this. You may even find my graduation thesis there on gundrilling (which used to be used for drilling barrels, but is nowadays a 'normal' process, also used for drilling short holes). It's in English, for anyone interested.

Again, thanks anyone for the thorough explanation and links!


Bwana John
March 3, 2005, 12:35 PM
I have found it works very well.

March 3, 2005, 01:06 PM

Did you just suggest that an AK might jam?!!!! :eek:

Isn't that statement some sort of blaspemy?! How could you say such a thing?

Now, for penitence you need to say, "Hail Kalashnikov" 100 times while shooting an AK. :D

Jim K
March 3, 2005, 05:29 PM
Just FWIW on "gun drilling". I once heard of an engineer for a weaving company who decided to lubricate one of the machines through a hole in a supporting rod. On his own, he spent tens of thousands of dollars of the company's money re-inventing the whole process of deep hole drilling. Finally, after a couple of years and many tries, he got a hole through the steel rod without running out. He was proudly demonstrating his idea to a group of company executives when the company president asked, "Why didn't you just use an old rifle barrel?" Being a good liberal, nothing connected with guns had ever crossed his mind. I guess he kept his job, but he learned a lesson.


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