SpudFiles

Posted: **Thu Apr 03, 2008 1:57 pm**

this was posted in JSR's making the blow forward bolt work thread, but i decided to start a new thread on it per ant's suggestion.

question, anybody know any good flash animation how-to's so i can make one for this?? It really needs one

woooooooot!!!!!! picture!!!!!!!!!... JSR'S thing i was talking about can be found here.
http://www.spudfiles.com/forums/6mm-sem ... mag-t10075. html

its not so much a blowforward bolt as it is a blowforward and blowback bolt combined into good old .......borwrack goodness...lol..... SmileSmile Very Happy

the only problem i might see is figuring out how to get it to fire so the bolt gets pushed back before the valve triggers again.. I figured out though that i can adjust that by increasing and decreasing chamber volume and pressure.
Good old high school gas laws come into effect here! (wait, i'm still in high school...lolz..)

oh yea, the back part is BTB's marble machine gun bolt. Take a look at his thread for details about that, that's not what i'm focusing on.
sorry for the double post, just wanted people to notice this..
I'm soooo pumped up about it!! can't wait to test it!!!!

please don't start ripping on it right away about how bad I will fail. I'll just try even harder to prove you wrong... give it a chance. k you don't need a spring, because it operates similar to an AK47- the air behind the projectile goes up that black tube and pushes the bolt back again in place. Then it fires, the projectile goes down the barrel, air goes up the black tube, pushes the bolt back, and the whole process begins again.

I should learn how to make animations... anyone know any good tutorials??

An animation for this should clear it up for a fair amount of people.

I'll get it working as soon as i can, all i have to do is make a run for the hardware store. The prototype will be small scale first, probably inside a large syringe so i can see what is happening and tune it. I'll post pictures and a video when i get it operational.

So what kinda valve are you using here? A slide over valve>> or a poppet one? I dont c the benefit of this one over the blowforward poppet breech. You will always experience problems with recocking when the pressure of the airsource drops. The best I idea I have seen so far is the one of jack> a piston with a poppet at the back. The problem is that it needs lots of parts. But yeah go for it; it will prob look pretty cool. But keep in mind> a gun like an ak always has the same pressure as each round contains roughly the same amount of energy.

Btw why dont you post this under your own name and not jacks? Give urself some credit/respect:) Its also hard to find things back when these posts become so long (8 pages).

'll post a new topic for it. the benefit of this would be no spring would have to be used to recock it, thus allowing a faster recock time than a spring would be able to do. Even if you got a super strong spring, your air flow would have to fight that spring just to push the bolt forward. WIth this design, there is no fighting, its unopposed pushing for firing and recocking. and yea pressure drops might be a problem.... but not necessarily because as the pressure to recock goes down, the pressure to fire will also go down. TO combat this, I'm going to use some super thin o-rings so there is not as much resistance. I might lose a little air, but when i run this at the 300 or up PSI i plan on for my marble gun, it doesn't really matter now does it.

I'll have to test it.

Will be a new thread about this shortly. I will put quotes in it of our discussion of it as well.

Posted: **Thu Apr 03, 2008 2:47 pm**

I still don't get it

Posted: **Thu Apr 03, 2008 2:55 pm**

k, i'll work on getting an animation of it up as soon as possible. how do you create your animations??

Posted: **Thu Apr 03, 2008 3:07 pm**

I make the different frames with MSpaint, then put them together with Jasc Animation Shop.

Posted: **Thu Apr 03, 2008 4:03 pm**

k. I will get an animation up right now. Working on it as we speak. I will post it as soon as i can. Speaking of which, how do i post animations? can i just upload them to photobucket and then post them as normal or how??

Thanks,

Posted: **Thu Apr 03, 2008 4:13 pm**

I kinda get the picture, but, why use pneumatic actuation in both ways (blow-back and -forward)
If you just use a spring then you can simplify it.

Posted: **Thu Apr 03, 2008 5:35 pm**

you know gas operated loading system arn't very practical in low presur pneumatic loading system, gas operation in guns is practical because many powerful rifle rounds are too strong for direct blowback and open too fast so gas operation is used to slow the bolt opening, the presure in a gun barel when fireing is thousands of times more powerful than that of any homemadeairgun

there is definatly not enough power from the tapped gas to counter the air source, thats like trying to use a gas operated system to put the bullet back in it's shell, and their is no mode for the presure to acumulate exept for the friction in that green seal, which that friction must be countered by the force from a small bit of tapped gas from the shot which only had just enough pressure built up to to push the bolt off the green seal

Posted: **Thu Apr 03, 2008 6:32 pm**

its not countering the air source, because the air source won't be operating when the bolt is being pushed back, the chamber will be filling when it is getting blown back. plus it won't be low pressure, it will be operating at around 300 PSI or more.

The reason I designed this is that there are problems with using springs.

1) The air has to fight the spring to blow the bolt forward, making it slower and you have to use more air than my design
2) The spring takes longer to push the bolt back than air will.
3) WHile it might seem its fighting the air that's blowing the bolt forward, its really not. Instead, the bolt gets pushed forward, the air behind the marble pushes the bolt back WHILE THE CHAMBER IS FILLING UP AGAIN. maybe i should have mentioned this will be used with a QEV popoff combination so the chamber will be filled for a short amount of time... woops sorry if i didnt mention it. so the bolt will be pushed forward by air already pressurized in the chamber... I'm working on a prototype right now..

ILTBTU

Posted: **Thu Apr 03, 2008 8:17 pm**

Iknowmy3tables is right, 300psi IS low pressure compared to the 58,700psi of the .30-06.
The valve won’t be closed by the time the gas hits the gas tube, your going to need to have more surface area on the gas piston than the back of the blow-forward bolt. Other wise the gas system won’t be able to overcome the blow-forward bolt.

300psi gives it a chance, remember: “it’s all about the cubic inches.”

I plan on using gas operation, only I’m goin’ with John Browning’s M1895 (potato digger) type gas system as it allows for more leverage.

It’s a good design though.

Posted: **Thu Apr 03, 2008 8:43 pm**

k well maybe i'll have to revise it. i'll have to look at what you are talking about

Posted: **Thu Apr 03, 2008 9:03 pm**

Here’s a few links to help you out:

patent for the Model 1895
another design that allows for added leverage, also by John M. Browning

Good luck to ya'!

Posted: **Wed Apr 23, 2008 5:28 pm**

I was watching the Military channel, and i think one of the original armalite m16's had an automatic blowback system that worked like this, you might want to do some digging around on google patent search.

Posted: **Thu Apr 24, 2008 4:00 am**

igpay wrote:I was watching the Military channel, and i think one of the original armalite m16's had an automatic blowback system that worked like this, you might want to do some digging around on google patent search.

All ARs (aside from the pistol calibre submachinegun versions, which use direct blowback like most similar designs) use a gas driven rotary lock bolt that needs high (well over 10,000 psi) pressures to function reliably, and therefore isn't really transferable to spudguns.

Posted: **Thu Apr 24, 2008 4:16 am**

a good example would be some of the animations on youtube of the ak 47

Posted: **Thu Apr 24, 2008 4:33 am**

ajdevi92 wrote:a good example would be some of the animations on youtube of the ak 47

Or you could take a look at this handy animation on howstuffworks.com

SpudFiles

my bolt action, combination of blow forward and blowback

my bolt action, combination of blow forward and blowback