Little help with my first prototype

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andrex66
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Thu Mar 17, 2022 4:11 pm

Hi all, I would need some help with my first "air gun"
Actually is based on QEV + Slide valve, I tried to use a hammer valve but at just 4 atm it was so hard to open i just literally needed to hit it with a real hammer, poor design by me, I suppose.
I can't make a spring loaded hammer atm,so i went with a slide valve.

question: I've read that the chamber volume needs to be a little more than the volume of the barrel, so that the pellet is propelled as long as it's in the barrel and no air is wasted
This is my first attempt:
20220317_213646.jpg
Image

the chamber "A" is a 1" tube, 10 cm in length, the barrel will be an aluminium tube, inner diameter 6mm, length 100 cm (or less).
I think "A" is way overdimensioned?
The main tank is filled via the schrader valve on the right
I can only fill it with foot pump or bike pump, max 10 atm

I would like to balance number of shots and power, could someone give some advice, apart from "dump that **** and buy a real air rifle :D "?

Thank you in advance!

pls excuse my english
Andrea
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Anatine Duo
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Sun Mar 20, 2022 8:56 am

Looks fun!

I agree A is oversize. The reservoir will lose pressure every shot, and if A is not very much smaller than the reservoir, that loss of pressure will be quite noticeable every shot. The hammer valve can have a self regulating effect but that is totally different technology. I have a slide valve design I'm working on but hopefully it will have a regulator on it.

You could use some epoxy or something to take up volume in A, but first I would try it out as it is to see how you like it.
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farcticox1
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Sun Mar 20, 2022 3:54 pm

Those little 3/2 normally open lever valves make good triggers.
20171207_211320.jpg
You should get good results with a barrel down to even 400mm
I got 860fps with 0.12g BBs @ 150psi with this, chamber is big, barell is 400mm
semiauto (1).jpg
andrex66
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Tue Mar 22, 2022 6:02 pm

Hey guys, first of all thank you so much for your answers.
I managed to get a copy of GGDT (the site is unreachable, so I got it from web.archive.org).
Started playing with some simulation, one thing I wonder is: if I double the chamber length (so doubling its volume) and increase barrel diameter, do I get more energy and so a higher speed at the muzzle, at the expense of more air wasted? Just trying to get a balanced design

What is the "Pressure Drop" on the left? Is the "air" expended for each shot or the pressure remaining in the reservoir?
Clipboard01.jpg

Sorry to bother the forum, all these things are new to me :cry:

thank you in advance,
Andrea
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Sat Mar 26, 2022 7:47 am

I think that the pressure drop is for the chamber. When you see the warning about barrel choking flow it's a sign your chamber is too large for the barrel... should be nice and loud but maybe not the balanced performance you want.

Increasing barrel diameter nearly always increases energy, and velocity if projectile mass is the same.

Yes larger chamber will give more energy to a point, and also drop the pressure in your reservoir more.
andrex66
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Wed Apr 27, 2022 2:47 am

Work in progress.
Managed to make the stock (it took forever!) using two wooden board and a plywood board for reference, modeling and carving them for inletting the parts was quite hard with hand tools, huge respect for those who didn't use power tools and got pro results.

Trigger ready, I had to use two springs for the upper part 'cause the spring on the slide valve is quite strong and a single spring on the trigger couldn't hold the valva in place. If someone has a better design I would be interested, it's kinda working but maybe there are better solutions.
Cheers,
Andrea
stock1.jpg
stock2.jpg
stock3.jpg
trigger.jpg
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Anatine Duo
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Sat May 07, 2022 7:26 am

That is a lot of work!

Nice to see a mechanical trigger. Also the metal liner to hold the trigger and sear is a great idea.

There are several other ways to set up a sear to hold back the valve but would require almost total redesign. If you can get yours to work I would stick with it. Basically I would set up the sear so the pivot is at the far left. The slide will push the sear against the pin and be jammed until the right side of the sear is lowered. The trigger could be part of the sear but might feel weird.

It looks like you could eliminate the trigger return spring. The trigger side of the sear will press down on the trigger and hold it in place... I do that a lot in my designs (doesn't always turn out the way I think, but when it does it's an elegant solution)

We could start a whole thread on triggers... I have had a life long interest in them on crossbows, firearms, and spudguns.
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