Teach me about gas systems!

[DrAlexanderTobacco]

This is wrinkling my brain

[Stuey]

This awesome! Booey's doing a great job of systematically explaining GBB functionality, exactly what I was hoping for in this thread

[BaBaBooey]

Apologies for the multiple posts in a row...if anyone cares, this amazing air gun design was first introduced to me as the "middle shoot" mechanism. In Japan, gas blow back designs were initially classified under three different categories:

 

1. After-Shoot (New MGC/MGC Glock 17)

2. Middle-Shoot (Marui P226)

3. Pre-Shoot (WA M92F - the first version)

 

When middle-shoot was first shown to me, the slide/block carrier may start to move back while the BB is actually leaving the barrel. After-shoot is when the BB is launched after the blowback occurs and finally pre-shoot where the BB has fully left the gun and blowback occurs. Some of the very early middle shoot guns were fairly bad, because the timing wasn't perfected. However, once all the components started to come together and air gun designs in Japan started to improve, the middle shoot became the most efficient and most effective out of the three.

 

Prior to the perfected middle shoot was something called the Air Shaft Control System or ASCS Unit...this is the HPA unit that was first developed by Youth Engineering and various off shoots of ASCS made by Plum Project, Technasia, etc. In my opinion, ESCORT perfected the ASCS.

[renegadecow]

I always figured TMs GBBs (post M92F) were pre-shoot systems as designed by Tanio Kobayashi? Using a floating valve keeps it open until the bb leaves the barrel creating a negative drop in pressure. The floating valve closes, diverting gas backwards which only then starts the blow back process. Unless you have the floating valve mangled up or obstructed half way I don't see why blow back might commence with the bb still in the barrel.

http://www.redwolfairsoft.com/redwolf/airsoft/ReviewDetail?reviewID=199

[BaBaBooey]

I always figured TMs GBBs (post M92F) were pre-shoot systems as designed by Tanio Kobayashi? Using a floating valve keeps it open until the bb leaves the barrel creating a negative drop in pressure. The floating valve closes, diverting gas backwards which only then starts the blow back process. Unless you have the floating valve mangled up or obstructed half way I don't see why blow back might commence with the bb still in the barrel.

http://www.redwolfairsoft.com/redwolf/airsoft/ReviewDetail?reviewID=199

 

I admit I'm not really too knowledgeable on this classification system as well as the science of pressure and gases...I'm basically regurgitating what people far smarter than me has explained to me. A fellow by the name of Mr. Matsumura first introduced me to this classification system (it's hard to translate, but he's now a public relations/marketing person for Tokyo Marui...I don't know him well at all, but he did give me his card once). He explained to me that their blow backs are middle...I guess the floating valve on a negative pressure system can begin to close while the BB is still in the barrel? He's also not an Engineer or Toy Gun Designer so he could be wrong.

 

EDIT: ok, so according to self proclaimed "experts", Marui negative pressure system is most definitely middle shoot. Do you still have the red barrel plug that comes with Marui GBB pistols? Fire your gun with it plugging the barrel (as if the bb is still in the barrel) - the blowback still occurs. I'll post why this happens as it was explained to me when I talk more about the cylinder components.

 

FYI, "Tanio" is not his real first name (it's technically the name of his company)...he introduced himself as "Tazo" (at least, he used to...unless we're thinking of two different people). I'm 99% certain he claims he and a few of his assistance designed pre-shoot guns while at MGC (the Glock series)...it was a long time ago and my notes may be wrong. EDIT: same experts classify the MGC Glock series as pre-shoot. He more less designed a blow back system out of the MGC M93R-AP as a starting point.

[bankz5152]

Bloody hell nice job booey!!

[renegadecow]

I dunno about the barrel plug, my TMs are cross shaped so allow gas to escape on the sides.

 

edit:

Here's a slow motion compilation by Nishiyan. You can see in just about every TM gbb he shoots has the slide start to move only after the bb has left the barrel.

 

Regarding the whole middle shoot issue, I'm guessing the "slide may move with bb in barrel" could have meant that the gun will still cycle in the event of a barrel obstruction.

[blobface]

Threads like this reminds me of why I love this forum.. 

[BaBaBooey]

 

Here's a slow motion compilation by Nishiyan. You can see in just about every TM gbb he shoots has the slide start to move only after the bb has left the barrel.

 

Regarding the whole middle shoot issue, I'm guessing the "slide may move with bb in barrel" could have meant that the gun will still cycle in the event of a barrel obstruction.

 

 

Those guns in the video are middle shooting. The middle shoot is actually an interesting part of Japanese airsoft history...again, I'm not an expert on this so I'll try to give a general overview. First, the belief that MGC created the gas blowback pistol as we see it today is not correct. Again, Mr. Kobayashi himself says that the original MGC's Glock series is an after-shoot system that has been superseded first by pre and then by middle-shoot. It's fairly evident when seeing the internals of any after-shooter that it operates VERY differently.

 

The original pre-shoot design was released by Western Arms where gas was used to both fire the BB, then redirected, to blowback the slide for reload. In 1993, they released the first pre-shoot mechanism inside their M92FS. The pre-shoot design soon became proprietary and is now protected by various patents and copyrights held in Japan by Western Arms. It is copyrighted/patented as the "Western Arms Magna Blow-Back System" and, according to people at WA, no other company in Japan can now legally manufacture and sell a pre-shoot gas blow back system (I know...it's weird).

 

Toy gun fans at the time were not happy; other companies had always had after-shoot gas blowbacks, often similar to MGC's (JAC Browning High Power Mk III, Tanka Colt 380, etc.), but no where near as good as the pre-shoot guns. If anyone remembers the Marui S&W M59 or MP5 gas blowbacks (ca. 1987), the natural state of the gun was with the slide/bolt carrier pulled back (when you store the gun, it is stored with the slide pulled back). When charged, gas pressure would close the slide and the pistol was ready to be fired (the Marui M59 used a re-fallible gas bottle that was inserted into the grip and a separate magazine that held BB's), but unlike the WA M92FS, blowback was achieved by releasing a spring which was in tension when the slide was closed.

 

The WA pre-shoot system was good, but not anywhere near as good as the guns seen today. Various toy gun companies in Japan, including MGC, started looking into releasing their own improved pre-shoot model without violating the WA copyrights (a little over a year later, Marui released their first version of their Desert Eagle). This is the origin of the "middle-shoot" system. Today, nearly every company released their own proprietary middle-shoot system that differs from the WA Magna; off the top of my head there is the Excellent Piston Unit/System-7, KobaExcel, Maruzen Advanced Shooting System, etc. On a side note, the modern Marui gas blowback is most similar to Marushin and not MGC...there are barely any differences between Marushin & Marui. Each system is different enough from WA's Magna system so as not to break any laws, but it's based on WA's pre-shoot concept of using gas to fire the BB and cylce the slide.

 

The modern Marui gas blowback pistol is designed to middle shoot - when gas is released into the cylinder, it travels down the barrel and back towards the piston at the same time (in Marui pistols, there is a component called the valve stopper that ensure this happens - again, I'll try to explain with photos and diagrams).

[BaBaBooey]

Let me first start with the photo below from Redwolf. Among other things, this diagram is NOT a correct representation of a Marui gun...the cylinder valve NEVER makes contact with the surface of the piston head (A). Again, the valve stopper prevents this contact and is not positioned correctly in their drawing. In the diagram below, there is no way the cylinder valve will ever move forward to close since there is no space between the back of the cylinder valve and the front of the piston head. Gas needs to get in between the two parts inorder for pressure to build and close the cylinder valve.

 

 

This is what the blowback unit of a modern Marui middle shoot system looks like, again from a P226E2. The components are:

 

A. Cylinder (sometimes referred to as Loading Nozzle)

B. Piston Cup (sometimes referred to as Piston Head)

C. Piston

D. Cylinder Return Plunder & Spring

E. Cylinder Valve (sometimes referred to as the "Floating Valve")

F. Cylinder Valve Spring

G. Valve Stopper

 

 

I tried to align all the parts (the red line) as it would appear inside the cylinder. What I want to stress here is that there is a gap between the surface of the piston cup ( C and the cylinder valve (E). The Valve Stopper (G) prevents the cylinder valve from making contact with the piston head and maintains a specific separation (H). This separation distance is also important for the gun to cycle properly.

 

For everyone that owns a modern Marui pistol, you can actually see this separation. Shine a light into the opening of the cylinder and you will see that the cylinder valve is NOT making contact with the piston head. As a result, when gas first enters the cylinder, it will immediate make its way down to the piston to start blowback and down the barrel to shoot the BB at the same time. This is the concept of middle shoot. As pressure starts to build between the valve and piston head, the valve will begin to move to the right and completely close.

 

You can simulate this closing...using a thin punch or screw driver, carefully place it through the opening and push against the cylinder valve (E). The valve will begin to move down towards the barrel and begin to compress the valve spring. When the valve spring is completely compressed, it will close the opening into the barrel. As a result, gas can now only move to the left, driving the blowback action (it won't move down back into the magazine). Once you let the valve go, it will return back into place as the cylinder valve spring (F) expands.

 

Also note that the surface of the piston cup is in alignment where the channel that moves the valve knocker lock down into the rear chassis ends. This alignment is extremely important for the gun to properly function and I'll try explain why. Strong hammer springs, recoil springs, and heavy slides will throw off this alignment.

 

Forum's really slow? So cont'd...

 

[Zombie00]

Just bumped into this thread, quite the interesting read up .

Can anyone give a thorough explanation on how the blowback system? I'm interested on adding a blowback mechanism to a NBB 4,5mm airgun, more specifically a Baikal Makarov.

Here is the best diagram of the gun that I could find:

http://www.makarov.com/graphics/co2/co2_cutaway.jpg

 

I know my way around solid works and I have access to milling machines. If I'm up to do this I would definitely re-made the slide in aluminum (to improve efficiency and get a snappier cycling).

[renegadecow]

More thorough than what BaBaBooey already put out? I don't think that's humanly possible. As for converting your Baikal into GBB, that's an even less likely probability mostly due to the magazine design. You'll have better chances in gutting it and stuffing it with gbb PPK/S internals.

[BaBaBooey]

I'll try to wrap this up soon...it's hard to describe the mechanics behind the blow back unit in flat 2D diagrams.

[blobface]

Even though this video is more specifically about RA-Tech's NPAS system, it shows how a WA M4 GBB unit works.

 

 

Here's a Baikal gbb prototype..

 

[Stuey]

Very sad that booey's fabled last installment never materialised, was very much looking forward to it

 

RA video is interesting though.

[BaBaBooey]

Working on vector drawings...a friend said she might be able to make a GIF