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semi auto questions

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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semi auto questions

Unread postAuthor: dyldo » Mon Dec 17, 2007 3:50 am

heres the plan.
making a semi auto mechanism for 6mm - 1/4inch projectiles using Clides slider design. the barrel and mechanism will be encased in pn18 22mm - 7/8inch pvc

i have made the chamber and am working on the sprinkler valve

my questions and concerns are:
if i release 150psi from the valve down the barrel into the slide will it hit the projectile out of the barrel before the air forces it out a bit like the pin in a nail gun?
also how much if any performance will be lost from diverting air around/through the slide?

thanks for any answers and comments.
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Attachments
16122007(002).jpg
another size comparison of the small valve
16122007.jpg
size comparison of the small valve
16122007(001).jpg
my marble cannon with the new cannon currently under construction
6mm semi (1).gif
the semi auto mechanism copy of Clides idea

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Unread postAuthor: jackssmirkingrevenge » Mon Dec 17, 2007 4:01 am

There's no doubt that the breech design works, right now I'm going for something similar here but hoping to use a constant flow of air for full auto fire.

if i release 150psi from the valve down the barrel into the slide will it hit the projectile out of the barrel before the air forces it out a bit like the pin in a nail gun?


The valve opening will be quite instantaneous so I wouldn't be too concerned, however you can add some sort of frction mechanism like an o-ring to keep the projectile in place, if anything to stop it from rolling out when the barrel points downwards.

also how much if any performance will be lost from diverting air around/through the slide?


Of course you're increasing the dead space and reducing the flow, however for a decent chamber size and pressure you should still get respectable performance.

I think a sprinkler valve is a bit overkill for a 6mm barrel, with this design I got very good performance using a simple blowgun - at 150 psi yours would be even better, as I'm limited to 110.

edit: Also, have you checked how long it takes the sprinkler valve to reset after firing? if it is too slow the system will be very wasteful of air.
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Unread postAuthor: dyldo » Mon Dec 17, 2007 5:31 am

i haven't finished modding the valve so im unsure at this stage.
i may just make that cannon a bolt action/breach loader. but seeing the semi auto i had to have one.
your designs have brought light to one of my incomplete projects.
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Attachments
pistol idea.gif
idea for a bb pistol forgot what type of valve it is though
pistol idea.gif (30.1 KiB) Viewed 690 times

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Unread postAuthor: jackssmirkingrevenge » Mon Dec 17, 2007 5:48 am

The above would be a manually reloaded piston valve. If you have two separate valves to both fill the chamber and pilot the valve, you could easily make it semiauto by incorporating it in your first design instead of the sprinkler. If i were you before making further progress, mod the sprinkler and see how long it takes to seal shut after firing.
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Unread postAuthor: dyldo » Mon Dec 17, 2007 6:03 am

i have already made a prototype of the piston valve but destroyed it because it didn't seal i have now realized i probably should have placed an o ring in the bondo/bodyfiller around the barrel for the piston to press against forming a seal.
ur 6 mm semi is some what of a piston valve anyway.
i would like say a sniper the sprinkler and a semi auto or auto pistol type
so far now ill finish of the sprinkler make a sliding breach bolt or pump action maybe. i can always make another barrel later. and ill wait to see how ur full auto turns out then copy it :)
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Unread postAuthor: daberno123 » Mon Dec 17, 2007 4:21 pm

ill wait to see how ur full auto turns out then copy it

How will u learn? that takes all the fun out of it. how about you copy it but try and improve it? *hint*hint*
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Unread postAuthor: dyldo » Tue Dec 18, 2007 1:54 am

finished modding the valve today it resets fairly quickly. and since i already have all the materials to make the slide i think i'll give it a go and see how it turns out.
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18122007.jpg
18122007(001).jpg

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Unread postAuthor: Novacastrian » Tue Dec 18, 2007 2:01 am

I got scared when i saw that your cannons were under a cutting saw.
Nice work and good luck with your new "Jaunt".
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 18, 2007 3:02 am

very nice fitting you made there :) it should work well with a semi auto breech. As to full auto with constant flow, *stream of anglo-saxon profanities*
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Unread postAuthor: dyldo » Thu Dec 20, 2007 4:25 am

i wish i made that fitting. i had someone else make it for me (:
made some progress on the slide now to let the glue set. boring

anyone know how to rifle a 6mm - 1/4inch I.D steel barrel or how to make a tool to do it?
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Attachments
20122007.jpg
all the pieces of the mechanism
slide hasn't been cut to length at this stage.
19122007(002).jpg
cut out in two barrels with the slide and projectile in the middle. dremmels are

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Unread postAuthor: jackssmirkingrevenge » Thu Dec 20, 2007 1:09 pm

dyldo wrote:i wish i made that fitting. i had someone else make it for me (:
made some progress on the slide now to let the glue set. boring


Tell me about it, I hate the "curing" phase of the build :(

anyone know how to rifle a 6mm - 1/4inch I.D steel barrel or how to make a tool to do it?


It's easier and probably cheaper to buy a 0.25" airgun barrel
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Unread postAuthor: ALIHISGREAT » Thu Dec 20, 2007 1:21 pm

It's easier and probably cheaper to buy a 0.25" airgun barrel


where can you buy air rifle barrels? i have looked on the internet but i can't find anything :(
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Unread postAuthor: jackssmirkingrevenge » Thu Dec 20, 2007 1:32 pm

ALIHISGREAT wrote:where can you buy air rifle barrels?


Have a look through the
Airgun spares section of the Chambers site - for example, Crosman 0.177 rifled barrel for less than 20 quid.

It would be wise to look through the cheaper manufacturers (gamo, crosman etc.), for example if look at Weihrauch barrels they get a little pricey.
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Unread postAuthor: ALIHISGREAT » Thu Dec 20, 2007 1:53 pm

aww they are catergorised by model... so i can't just look at all the barrels in one section, do you know of a .22 air rifle with a long barrel?
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Unread postAuthor: MaxuS » Thu Dec 20, 2007 1:58 pm

If you look in the PCP section (if they have one..) then there should be some longer ones with threaded ends.
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