Inside an AK 74, in slow-motion!

[estousandy]

This is too good. Enjoy!

[youtube][/youtube]

[StampMaster]

Nice video. Thanks for sharing..

[aadhaulya]

very nice, I really enjoyed watching the video.

Regards

Atul

[brihacharan]

Thanks for sharing this wonderful / illustrative video clip
The precise use of the blow-back gas to cock, fire & eject ......was indeed a treat to watch
Briha

[timmy]

Good one, estousandy. What I found interesting is that, even without the gas tube, the bolt carrier/piston gets enough oomph from the recess in the gas block alone to work the action. This clearly shows how the direct impingement system used on the M16 gets enough "push" to accomplish the job without the need for pistons and gas tubes.

It was also interesting to see the action's loose tolerances, with all of the pieces flopping about on firing. Of course, the only area where a precise fit needs to be provided is the locking of the bolt, and this video didn't and couldn't show that, but it was plain to see how loose things actually are in Kalashikov's design.

When the shooter took off the gas tube, I'll bet he was glad he had that glove on!

[aadhaulya]

Tim,

Was the gas tube supposed to be fitted on top of the barrel, where the piston sort of thing is flopping around? It was sometimes hitting the outer area and then sliding in.
Can you please give a little detail on how it operates and how the bolt is locked and released??

Regards

Atul

[timmy]

Atul:

Yes, the gas tube fits behind the recess you see the piston entering. The other end fits into the receiver. This tube has a number of vent holes and is normally covered by a wooden upper hand guard so that gas vented to the piston is harmlessly dissipated.

The gas block, into which the head of the piston fits, has a passage connecting to the barrel. When the fired bullet passes the port in the barrel, which is the opening of this passage, the super high pressure gas in the barrel blasts into the passage and shoves the piston back very hard, as you can see in the video.

The piston is connected to the rod you see, which is part of the bolt carrier. This carrier is the part you see going back and forth because the sheet metal receiver cover is removed.

The bolt carrier has the bolt itself mounted in a hole, below where you can see the top of the bolt carrier. It looks a lot like a bolt from a small bolt action rifle withe the back and the handle cut off. It has an extractor, a lot like some bolt action rifles have, a firing pin, and a pair of loving lugs at the front. On each side of the bolt.

The bolt locking lugs rotate about 45* to engage shoulders in the receiver, at the back of the barrel.

Now, what turns the bolt?

In the side of the round bolt, there's a spiral groove into which a projection in the bolt carrier mates. When the gun is fired and the bolt carrier starts moving backwards, the bolt cannot move back at first. It is still locked into the receiver, containing the cartridge case and hot gasses in the barrel chamber.

But the projection in the bold carrier is in the bolt's spiral groove. The bolt carrier's projection in this groove makes the bolt twist. This is like the old style hand push drills and screwdrivers work, if you've ever seen one.

The bolt only needs to rotate about 45* and it is unlocked, so that it begins moving backward with the bolt carrier. The bolt, moving backward, pulls out the empty cartridge case by means of the extractor hook. The ejector then knocks the case out, and the bolt carrier cocks the hammer for the next shot.

A spring then pushes the bolt carrier and bolt forward, stripping a fresh round from the magazine and shoving it into the chamber.

Finally, the last bit of travel of the bolt carrier causes its projection to push against the spiral groove in the bolt, causing the bolt to rotate and lock up to the receiver again.

[aadhaulya]

Thanks Tim,

You have made it quite clear, but one doubt still remains. That is what makes the bolt carrier twist 45* to unlock it??
If the reverse pressure forces it to unscrew, then there would already be enough pressure in the reverse direction on actual firing of the round. So I presume that there must be some additional mechanical lock that prevents it from unscrewing due to the pressure.

Regards

Atul

[xl_target]

Thanks Tim,

You have made it quite clear, but one doubt still remains. That is what makes the bolt carrier twist 45* to unlock it??
If the reverse pressure forces it to unscrew, then there would already be enough pressure in the reverse direction on actual firing of the round. So I presume that there must be some additional mechanical lock that prevents it from unscrewing due to the pressure.

Regards

Atul

The bolt carrier must rotate the bolt to unlock it. In the locked position, the bolt cannot move backwards.
It is only after the piston comes back, moving the bolt carrier backwards with it, that the bolt is turned and unlocks.
The bolt carrier has to move backwards or the bolt will not unlock.

When the bolt carrier is all the way forward, the bolt is firmly locked in place. This is what contains the pressures caused by the powder igniting.
By the time the gas acts on the face of the piston, the bullet has left the barrel and the pressure starts to decrease.
So now the bolt can safely start to unlock.

[aadhaulya]

Thanks XL,

Now if my understanding is correct the bolt goes forward pushing the cartridge into the barrel and rotates due to the spring pressure locking it on to the barrel. The carrier follows the bolt and after the bolt has rotated and locked the carrier still moves a little forward locking the bolt in place to prevent it from rotating.
Now it will only unlock when the carries is pushed back from the locking position and now the carrier drags the bolt back along with it.
This sounds logical, if correctly understood by me.

Regards

Atul

[timmy]

Atul:

The bolt doesn't rotate directly by spring pressure, but spring pressure is involved.

If you can understand this business of the rotating bolt, which you see in most bolt action rifles, you will also be able to quickly understand some of the modern lever (like the Browning BLR) and pump (like the Remington 760) action rifles, as well as a majority of semi and full auto rifles, like the AK series and the M16.

Now, I want to say that my description is backwards with respect to the bolt and bolt carrier, but this isn't an impediment to the principles we are describing. Let me use some pictures:



This picture shows how the port in the barrel channels expanding gasses from behind the bullet to the gas piston.




This is the AK bolt. you can see the extractor hook that pulls the cartridge case out of the chamber. Also, you can see one locking lug that's sticking up in the air. The other locking lug is 180* opposite from it, on the bottom of the bolt face and toward the back.

The part I want you to really notice, however, is the part in the foreground that the bolt is resting on -- it is a rectangular lug.




Here is the front of a couple of bolts. The lug I'm talking about is upwards and rotated 45* to the right on both bolts.

In the back, you can see two bolt carriers. The one on the right has the gas piston and rod attached; the one on the left does not. The carrier to the left has an angular groove visible behind the part of the carrier where the gas piston attaches.

The round rearmost part of the bolt fits into the larger round hole in the bolt carrier. The lug I was speaking of will fit into the angular groove of the bolt carrier.




Here is the bottom view of the bolt carrier. You can see the angular groove I'm speaking of quite clearly. Toward the rear bottom of the groove, you can see how the groove is inlet into the body of the bolt carrier.




Now, let's put the bolt into the bolt carrier. You see the rear round part of the bolt going into the hole in the bolt carrier.

The lug I was speaking of (which is not a locking lug) is resting on top of the guy's thumb in the picture. When he pushes the bolt into the bolt carrier so that this lug aligns with the bottom of the groove, he will rotate the bolt so that the lug will slide into the groove.

Now, think and imagine: after the lug on the bolt enters this groove, if the man keeps turning the bolt, what will happen? The bolt will slide forward in the bolt carrier, because the groove will force it to do so.

This is the same as when the gun is fired, except instead of the bolt being twisted by the guy's hand, it will be the bolt carrier that will twist the bolt, because the lug in the angled groove will cause the bolt to twist the bolt as the bolt stays forward and the bolt carrier is pushed back by the gas piston. The twisting action unlocks the bolt, and when it can't rotate anymore because it hits the front end of the groove, the bolt will be unlocked and move back with the bolt carrier.

Closing will be in reverse: as the unlocked bolt hits the back of the barrel and receiver, it can't go forward anymore, so the bolt carrier, which is moving forward, will twist it into the locked position. This will happen because the lug on the bolt will hit the back slope of the groove. The lug in the bolt will be forced to rotate as it moves back into the bolt carrier and the locking lugs will engage the receiver again.

[aadhaulya]

Tim,

This is somewhat like what I understood. But your pictures and explanation have cleared the whole process in detail.

Thanks

Regards

Atul

[Rrahulkumar]

Awesome video.. Thanks for sharing

Cheers..!
RK

[sa_ali]

amazing video, it making the action so clear