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LKSXXX
06-19-2007, 06:55 AM
I've been looking up on how this blowback system works because I couldn't understand it just from reading the descriptions about it, so I went after pictures/diagrams, etc. but still had some doubts about how it worked because most of the pictures available were taken from the French FA MAS, which uses an improved version by Paul Tellie from GIAT industries. This weekend I stumbled across a forum where the guy posted some pictures of the original patent of the system by Paul Von Király and finally understood. So, in case other people have the same doubts that I had, I decided to make an animation to clear thing up.
This server takes a long time to load the GIF, so try right-clicking the link and 'save as' (if the image doesn't show the entire cycle with the case being ejected, try downloading it from **********):
http://imgserv2.imagehigh.com/imgss/5995389_anim-animate.gif

**********:
http://**********.com/files/38086991/anim-animate.gif

Here are some pictures of the patent by Paul Von Király:
http://imgserv2.imagehigh.com/imgss/5995502_fig1.JPG
http://imgserv2.imagehigh.com/imgss/5995503_fig2.JPG

Here is a diagram of the FAMAS:
http://imgserv2.imagehigh.com/imgss/5995518_famasfig23.JPG

Please feel free to give me some feedback about the animation.

LKS.

Herrmannek
06-19-2007, 08:50 AM
idea behind all delayed blowback delayed designs is simple, it works like a gearbox set to high gear.. You need to press pedals harder but you move further for the same amount of turn.

So when breech part of bolt moves only a little protecting case from rupturing and opening breech before bullet leaves barrel. Because of the lever action, the rear part covers greater distance. That means it does it with greater speed. And as you know for system of the same mass, more speed equals more energy and more force needed to push the whole assembly. Thats why you can have a lighter assembly or use stronger rounds... As for the animation, the part that works for me is okey. lever is fixed to the body of the gun(all kinds of levers need a fix point to work :) , for few mills of move of breech part of bolt, rearward(the one on top) part moves faster covering bigger distance...

LKSXXX
06-19-2007, 10:14 AM
Yes! Exactly. The comparison with a gearbox is excellent, thank you.
As for the lever being fixed to the body of the gun, do you mean it has to be fixed to the reciever? In the FAMAS it travels with the bolt (it isn't exactly fixed to it).

Do you know any particular drawbacks of this system? I mean, most people say it's not very good because it's only used in very few rifles. But that's kind of like saying Ferraris aren't good because very few people have them, right?
If it isn't a reliable system, then that story about the Korobov TKB-517 being more reliable and accurate than the AK-47 isn't true because we would be comparing a lever-delayed blowback rifle with a gas-piston one.
Does anyone know the specific disadvantages? Production costs? Weight?

LKS.

Herrmannek
06-19-2007, 11:40 AM
Yes! Exactly. The comparison with a gearbox is excellent, thank you.
As for the lever being fixed to the body of the gun, do you mean it has to be fixed to the reciever? In the FAMAS it travels with the bolt (it isn't exactly fixed to it).

Do you know any particular drawbacks of this system? I mean, most people say it's not very good because it's only used in very few rifles. But that's kind of like saying Ferraris aren't good because very few people have them, right?
If it isn't a reliable system, then that story about the Korobov TKB-517 being more reliable and accurate than the AK-47 isn't true because we would be comparing a lever-delayed blowback rifle with a gas-piston one.
Does anyone know the specific disadvantages? Production costs? Weight?

LKS.

By fixed I mean that when levering action is happening lever must be supported by something fixed in relation to the bolt assembly, without it you can't get lever action... In rifles after lever is fully deployed, it goes away from bolts way or is disengaging from the lug it sits in and is carried by the bolt(this seems to be case of famas and patent pics of rifle you posted)...

As for disadvantages its a still blow back system so cases are moving in chamber while still under pressure, there are some timing issues when changing pressure, bullet weight and so on... As for advantages, probably most important one is barrel can be made really free floating...

Herrmannek
06-19-2007, 07:10 PM
Those aren't delayed blow back but locked breech... Another animals... blow back designs operate solely on the butt of the case pressing on the bolt head, in the locked breach rifles bolt is locked rock solid, so energy to operate bolt is usually taken from the barrel witħ use of gas tube or piston...

As for gases blown back into bolt chamber in the FAMAS. AFAIK chamber of this rifle have Revelli grooves to equalize pressure inside and outside of the case and they can lead to fouling. But don't quote me on this...

SOG
06-20-2007, 01:58 AM
ah thank you. sorry i misread earlier.

LKSXXX
06-20-2007, 06:17 PM
Thankyou for the pics nevertheless.

LKS.