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Semi-Auto valve help

This area is for the discussion of BB or airsoft sub machine guns, and or other small arms such as pellets.
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Semi-Auto valve help

Unread postAuthor: qwerty » Mon Aug 31, 2009 12:16 pm

Right, i want to make a semi-auto air pistol but im struggling to choose a valve to use.
which valve do you reccomend i make?
i need one thats simple to make and dosent require machine work

Hammer valve
JSR's blow forward bolt
or anything else

i need a semi-auto expert to help me choose or show me any other valve

Thanks
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Unread postAuthor: THUNDERLORD » Mon Aug 31, 2009 12:25 pm

What caliber (diameter bore) and ammo do you plan to shoot?

For "semi auto", "doesn't require machine work" and simplicity,
a QEV probably.
Course most designs on here don't require advanced machining.

BTW, JSR's "Blow-forward bolt" is not a valve for pneumatics, just a bolt, to load the projectiles automatically, and still needs a valve to pulse the air/gas. 8)
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Unread postAuthor: john bunsenburner » Mon Aug 31, 2009 12:31 pm

What machines do you have at hand, i have plans for a semi auto valve, which is doable with only a drill press, but fairly hard. You would have to wait as I won't post the idea, or the gun i will build using it(should be my first gun i think) before the end of the contest, so that no one takes the idea(it will not be in the contest, as i don't have the time to build it until then).

However the main parts to a semi auto valve are as follows:

A part to block air flow from the main chamber to the secondary chamber
A part that opens the secondary chamber to the barrel
A part that reloads(if this is part of the valve it is ver useful, mostly)


If you can put these parts into a valve you are sure to get a semi auto design, however some valves operate differently and are still semi auto, they simply just open for a short amount of time leaving enough air in the chamber for more shots(hammer valves).

Its up to the tools and the cash you have to decide what you can build.
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Unread postAuthor: qwerty » Mon Aug 31, 2009 1:08 pm

i dont have any access to anything other than a drill and alot of other hand tools but i might be able to get pistons and things machined for me
Calibre: um probably .177
how do you make a QEV semi-auto. Just put a spring in it?
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Unread postAuthor: THUNDERLORD » Mon Aug 31, 2009 1:10 pm

...how do you make a QEV semi-auto. Just put a spring in it?


Yep, That's all you need to do. :P
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Unread postAuthor: qwerty » Mon Aug 31, 2009 1:16 pm

yeah but if theres 300 pounds of air pushing on the spring how does it reset it
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Unread postAuthor: PVC Arsenal 17 » Mon Aug 31, 2009 1:28 pm

Don't listen to him.

It's very simple. Connect a three way, normally open valve to a quick exhaust. This setup also allows you to incorporate a pneumatic cylinder if you need to actuate some type of loading system.

I feel like I've been posting the same thing constantly lately.

Look for a normally open valve such as the Clippard MJVO-3.

You can also use Slide check valves (sleeve valves). I recommend McMaster part# 4622K51

There is also the Pneumadyne A11-31-44


If you need more help, ask me or POLAND_SPUD. It's safe to say both of us have conquered semi-auto. There are others besides us, but not many of them post much.
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Last edited by PVC Arsenal 17 on Mon Aug 31, 2009 1:30 pm, edited 1 time in total.

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Unread postAuthor: THUNDERLORD » Mon Aug 31, 2009 1:30 pm

That was a bad joke.
I hate to lie.
Any way, looks like you live in UK so certain semi-auto ideas are probably not available.

Semi-auto is more difficult than fully-auto "cloud" or "vortex".
Since it's .177 cal. , maybe you could attach the trigger to the magazine, so when the trigger is pulled slightly more than .177" or 4.5mm rearward, the pellet/BB drops through a hole in barrel,
the sleeve around the barrel blocks the hole in the barrel,
when the trigger is pressed a fraction of inch further an electrical contact switch is closed, activating a pilot for the QEV.

For .177 to get decent results, higher pressure is needed.
(CO2, shock pump, helium etc.)....
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Unread postAuthor: john bunsenburner » Mon Aug 31, 2009 1:47 pm

Also ussually round ammo is easyer than shapped ammo like pellets.
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Unread postAuthor: qwerty » Mon Aug 31, 2009 1:56 pm

yeah thanks for the help ill be using around 300 psi
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Unread postAuthor: THUNDERLORD » Mon Aug 31, 2009 2:37 pm

yeah thanks for the help ill be using around 300 psi


300 PSI is reasonable.
You could easily fill a pressure vessel to that and higher using a fridge compressor.

Since it's .177 I don't understand the urgency for semi-auto really.
If it was airsoft for games or paintball, semi-auto would make more sense IMO.

But for plinking, and other .177 stuff, being able to reload and shoot within seconds at a decent velocity..., semi-auto is not necessary.
A fairly rapid bolt action system etc. will be just as fun IMO.
This is a pistol design and all but still...something to think about.

If you go for higher pressure/velocity in a pistol size package, semi-auto will be even less important in .177.
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Unread postAuthor: qwerty » Mon Aug 31, 2009 2:40 pm

yeah but but it woud take a while to pump it up with my shocky
so i want to have mutiple shots before pumping it up again.
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Unread postAuthor: POLAND_SPUD » Mon Aug 31, 2009 4:23 pm

@qwerty
both PVC_arsenal 17 and TUNDERLORD are right.... QEV + 3 way valve is probably the best and easiest way to build a semi auto...

THUNDERLORD is right that it isn't the best idea to build a semi in .177 calibre... and it's even worse idea to build a semi auto pistol...
I htink you would be better off with something like a daisy BBgun (yeah I know it's not a true semi) or an airsoft pistol running on greengas


I suspect that you don't really know yet what would you like to build... Am I right ?? don't get me wrong it's a good thing and IMO the most important part of designing your gun...
you should spend some time thinking what would you like to build and check if it's feasible, how powerful would it be, how difficult to build etc.

for example you might consider building a high pressure BBMG with a detent... people talk about it here from time to time but no one really build one (it's not that the design is complex or requires machining...

I think that no one attempted it yet) I know it's not what you are looking for at this moment but it's just food for your thought (and you could build it in .177 calibre :wink: )
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Unread postAuthor: spudtyrrant » Mon Aug 31, 2009 4:30 pm

qwerty wrote:yeah but but it woud take a while to pump it up with my shocky
so i want to have mutiple shots before pumping it up again.

my friend if you want a semi that will fire more than 3-4 shots you may want to upgrade your air source i would suggest at least an hp pump if you want to make a high pressure semi feasible
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Unread postAuthor: john bunsenburner » Tue Sep 01, 2009 10:09 am

Well really a .177cal semi auto is feasible if you have one of the following:

-access to 5-10fridge compressors, a scuba or other compressed air tank rated 3000 or more psi(just in case!!!) and the tools and fittings to connect these to a large unit for HPA(800psi is realistic)
-access to a large amount of highly compressed gasses(air or N2 are the two feasible ones).

Then one could get decent velocity and have some fun without he fiddling involved in such a design. I figure others will agree...


For a semi auto I would recommend nothing under 7mm ammo, the one i am planning to build will use either 8mm or 9.5mm sling shot ammo. Marbles are a great ammo for them too, but not in my design as that would take a huge piece of aluminium(i like working small, i got enough big parts to work with already ;))and so isn't feasible for me, but Marbles are highly recommended for first time semi builders, at least that is what I think.

How about you try what has been recommended with either Marbles or large ball bearings?

Also I think a nice AK look or some old (semi) auto would be nice. I want to put some wood on mine, it looks nice(if someone has inspiring guns which are simple and have a bit of woad and are NOT rifles or pistols but semi or full auto please post pics or names!)
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