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LKSXXX
06-19-2007, 05:55 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, 07:50 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, 09:14 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, 10:40 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...

SOG
06-19-2007, 04:25 PM
here you guys go, i found this image very useful for the technically challenged amongst us. (me)

http://www.lwrifles.com/tech.php

bad
http://www.lwrifles.com/images/Gif/DIAnim_3.gif

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good
http://www.lwrifles.com/images/Gif/PistonAnim_3.gif


Reports from military organizations who have compiled data, both empirically and through testing, deficits were found related to the issued legacy direct impingement carbine. In response LWRC set out to engineer, develop and produce a line of self regulating short stroke piston operated carbines for military, law enforcement duty and for civilian use. Those deficits of the legacy carbine identified were:

* Decreased reliability
* Decreased weapon service life
* Increase weapon down time due to repairs and maintenance
* ****ounced muzzle rise and recoil
* User maintenance intensive
* Environmentally sensitive
* Rapid heating in sustained fire leading to small parts and catastrophic failure
* Bolt lug failure
* Poor terminal ballistics related to the 5.56 NATO cartridge

LWRC engineered a solution that retains 80% parts commonality with the issued legacy carbine. The principal improvement comes with the incorporation of a self regulating short stroke gas piston system. The low mass "cup and nozzle" system uses 100% of tapped gas pressure to overcome the mass and resistance of the carbine’s moving parts. Once the mass and resistance is overcome, the system vents all excess gas in a "staged vent and dump" of residual gas.

The system is so efficient; it does this in only 6/10ths of an inch of movement. Extraction is far more positive and consistent shot to shot. Regardless of the loading, the piston only uses as much force as is required to cycle the action. No more, no less. The piston stroke is consistent even with a suppressor in use.

Most importantly, none of the trapped gasses are channeled into the bolt carrier group or the receiver of the weapon. That alone eliminates the intensive cleaning regime of the legacy rifle. It also means the bolt carrier group and associated springs are not subject to the searing heat of the tapped gasses which can lead to parts failure. All carbon is vented harmlessly under the hand guards or rail system. LWRC carbines are far more reliable regardless of user maintenance than the legacy direct impingement carbines.

The weapon chamber temperature is lowered as the upper receiver and rail system are no longer searing hot from tapped gasses and can now effectively operate as a heat sink conducting heat away from the receiver extension and chamber.

The short stroke piston system employing a "cup over nozzle" short stroke arrangement limit the reciprocating weight of the piston system and thus prevents disturbing the barrel harmonics and accuracy. With reciprocation of the piston cup, carbon is scraped away from the internal walls of the cup by the fixed ribbed nozzle and blown harmlessly out of the vent holes with the next cartridge fired. This makes the piston system almost maintenance free.

The differences in handling characteristics of LWRC’s weapons over the direct impingement legacy weapons are astounding. Recoil is light, muzzle rise is greatly reduced. It is most amazing that this can be accomplished with an LWRC carbine that is ergonomically identical with almost no weight penalty over the legacy direct impingement carbine.
Terminal Ballistics

While LWRC manufactures weapon in chambered in 5.56mm NATO, LWRC embraced the Rem 6.8mm SPC to address the poor terminal ballistics of the NATO cartridge that are exacerbated by carbine length barrels. 6.8 SPC was developed by military professionals for military professionals. The weapons platform is identical in size and weight yet firing 6.8mm SPC, twice the mass is delivered to the target when compared to 5.56mm NATO. The short pressure curve of 6.8 SPC makes it ideal for use in short barreled carbines and the optimal operating system is a self regulating short stroke piston.

Example:
55 Grain M193 (5.56mm) from a 10.5" barrel = ~2350 Feet per second
110 Grain Rem 6.8mm SPC from a 10.5 barrel = ~2290 Feet per second
Clean, cool, reliable, mission essential.

Herrmannek
06-19-2007, 06:10 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, 12:58 AM
ah thank you. sorry i misread earlier.

LKSXXX
06-20-2007, 05:17 PM
Thankyou for the pics nevertheless.

LKS.