coaxial bb gun on youtube

[lemming124]

Hey everyone,
I've been a member of Spudfiles for a while now, but this is my first post. I was looking at co-axials on Youtube when I came across the video below (please forgive me if I didn't correctly link, I have no idea what I'm doing). Anyway I thought this particular co axial stood out because it managed 8 decent (bb through a can esque) shots, off a single plastic bottle filled with air. After months of lurking around, I have decided that i will attempt to make a gun similar to this, mainly because: A) I don't have an air compressor, so anything capable of firing more than two shots off a single pump is fantastic and B) I definitely do not have the money to buy CO2 or propane etc. What do you think of this gun? am I being too ambitious in attempting to build it (having only built a basic ball valve pneumatic) ?

Thanks for your time (I'm sorry if I've broken any forum rules and wasted an admins time by making them delete this)


[youtube][youtube][/youtube]

[Crna Legija]

im not 100% sure but i believe that its just a coaxial with a spring pushing the piston forward and and tiny equalizing hole to alow you to vent. the spring should be just strong enught to push the piston.

[Brian the brain]

Thanks for your time (I'm sorry if I've broken any forum rules and wasted an admins time by making them delete this)

On the contrary, a very good first post.

Welcome to Spudfiles!

It's a coax with EQ hole and spring.A ballvalve separates the airtank from the rest.
The hole and spring keep the valve closed as it is filled from the chamber side.

It's not that difficult, just a bit of a challenge and opportunity to learn the basics. ( the simple addition of the hole and spring make it advanced even)

[Gun Freak]

I made a co-ax... Don't do it if it's your first! It is a pain if you are not experienced. Thats a good gun. But the power must deteriorate rapidly with such a small tank.

[chinnerz]

I made a co-ax... Don't do it if it's your first! It is a pain if you are not experienced.

disagree
http://www.spudfiles.com/forums/simple- ... 20115.html
thats mine, probably a lot more on here but cant be bothered looken.....

and i also agree with brian the brain, my first was a a help me post with 10 questions....

it looks like a barrel sealer

i recommend trying this if you have complete confidence in yourself
this is how they work

[littlebro05]

I've posted that before on the BB forums. And also wondered what it was but I'm thinking it's a coaxial that has a bottle on a bottom as a repeater to piston thingo ma bob...

Like Piston Coaxial Air Gun, but uses a small volume of air per shot so that way it can shoot more than 1 shot.

[lemming124]

WOW! thanks everyone. Ok so I've been snooping around the "how to's" and from what I've gathered I think I have the general gist of the self closing spring piston valve. I few things I am confused about:
- Equalising hole - what purpose does it serve? (I'm guessing to maintain equal pressure in the pilot area, so multiple shots can be fired off one tank)
- Purpose of the spring - If the air tank is separated by a ball valve, and there is pressure in the pilot area, shouldn't the piston seal the barrel by itself?

[Crna Legija]

Equalising hole is just that, a hole that alows equal pressure in the pilot side and chamber. it should only be 1mm at most

the spring pushes the piston forward when there is no air in the chamber after you shoot. it should only be strong enough to seal the piston against the barrel.

[Big-E]

Are you sure about it having a spring? Looks far simpler than that:

1: The bottle is pre-pressurized

2: He cracks the ballvalve and it actuates the piston forward. You can clearly hear the piston click shut when he pressurizes the chamber off the bottle. He just opens and closes the ballvalve quickly to charge up his air-circuit.

3: He may have an equalization hole, especially if the piston travel is short enough to seal so quickly.

I think it's an efficiently-designed piston valve, probably not spring-loaded, though. If it had a spring, he wouldn't need the ballvalve, right?

I do the same thing with Kopperbess, I get multiple shots out of a single fill, only difference is I have to shut the firing valve by hand before charging my chamber each time, that's why my next build will have a qev.

His chamber definitely appears to be coaxial, comparing that to the size of the bottle, I'd say he'd have enough air for about 6+ shots (assuming around 100-120 PSI fill pressure on a soda bottle like that.)

[POLAND_SPUD]

If it had a spring, he wouldn't need the ballvalve, right?

short answer -> he would need it

[jackssmirkingrevenge]

Youtube has a messaging service, why not just ask

[Big-E]

So, if I'm getting you PolandSpud, the spring is there to counteract the friction/weight of the piston?

[POLAND_SPUD]

the spring is there to counteract the friction from the piston

now I am lost... he needs a ball valve there that was my answer

he fills the gun from the chamebr side so so it is almost sure that there is a spring behind the piston...

anyway I was referring to the part about ball valve and whether it is needed there or not... IMO it is needed there as in this config the piston valve stays open as long as the pilot valve is open... so without a BV there you'd use more air than it's needed

[jackssmirkingrevenge]

So, if I'm getting you PolandSpud, the spring is there to counteract the friction/weight of the piston?

It would work something like this

[youtube][/youtube]

The piston (not airtight so no need for an equalistation hole) would open when the pilot is open, but as soon as the pilot is closed the spring would reset it. This means you don't need separate main and firing chambers with a valve between them.

[POLAND_SPUD]

that's the point...

as soon as the pilot is closed

......which means you've got approximately 10 - 15ms to close the pilot valve once the piston valve starts to open... if you don't you loose air which might not be the best idea because the guy stated that

A) I don't have an air compressor, so anything capable of firing more than two shots off a single pump is fantastic and B) I definitely do not have the money to buy CO2 or propane etc.