7mm Airgun- Concept Only, Design Needed!

[MisterDoctor]

So, a couple months ago I joined this forum to express an idea I had. I made one thread before, I want to make another to gather some more legitimate plans. I want to assemble a 7mm PCP airgun. I have the rifled barrel, lead ammunition, and all the tubing you could ever imagine. I need ideas on how to make this gun. Piston plans especially.

PLEASE. It's my first build, and has been driving me insane, this gun would be perfect for my area.

Vid related, it's what inspired me. Can you help me out?

[youtube][/youtube]

[evanmcorleytv]

We dont like to spoonfeed answers here. check the search, and read previous threads, but since you need help, I will refer you to an earlier thread EXPLAINING how QEV's, and piton valves work, and how they can be built. ALSO, why don't you just buy a QEV? They are a LOT cheaper than making one yourself, and that's what the gun in the video used.

The gun in the video used one of these types of QEVs:

http://www.ebay.com/itm/Pneumatic-Quick ... 424wt_1110

And here is how they work:



THIS IS A 3 PART SERIES SHOWING HOW THEY WORK:







THIS IS ANOTHER 3 PART SERIES ON HOW TO BUILD A LARGE PVC PISTON VALVE, AND HOW THEY WORK:

[Gun Freak]

Don't listen to Evan, that gun uses a custom built hammer valve. Nothing to do with QEVs
He posted a thread about the early on development of the mechanism. I'm sure you can find it by searching. Also try searching "hammer valve" and stuff like that, there are a couple threads where people showcase their homemade valves and such. Good luck.

[evanmcorleytv]

Don't listen to Evan, that gun uses a custom built hammer valve. Nothing to do with QEVs
He posted a thread about the early on development of the mechanism. I'm sure you can find it by searching. Also try searching "hammer valve" and stuff like that, there are a couple threads where people showcase their homemade valves and such. Good luck.

WHOOPS. I was thinking of Jules's AIRSOFT gun.. I didn't even watch the video, because I've seen them so many times. YES, he used a hammer valve, but a QEV would be the cheapest, and easiest thing to do with low pressure..

[Gun Freak]

Now Evan is probably right. QEVs are cheap, simple, and easy to work with. Check out JSR's semi auto for under $20. Perfect example. Then you add a bolt action loading mech or simple breech load or whatever you want, and you have a nice pellet gun.

BUT,

I understand you'd like to build a PCP... I'm on the same quest as you right now... I have found inspiration by Jules also, and members here too. There are lots of examples of simple hammer valves on the site, you just need to look hard. It's not something you need "plans" for... They can be pretty simple.

[MisterDoctor]

Thank you. Is there a link I can follow to JSR's build? Also, I tried to build a QEV myself but I don't think i made it correctly.

Here is the basic design of what I threw together.

[Gun Freak]

Well did it work?? Lol.
There is no way in hell that will work. What would happen if you dumped the pilot valve? All the air would go out the pilot valve. The piston is supposed to separate the pilot from the chamber... You didn't research enough.

The link to JSR's project is on top of the web site, it says "SEARCH".

Seriously.

I gave you the name of the thread.

Semi auto for under $20.

[MisterDoctor]

Yeah. Already found it, just too bored to edit my post. Thanks. And I didn't plan on trying it, because I knew something is wrong. My forehead hurts from all the slapping.

So I suppose I'll make it semi. Seems legit. I'll be back, soon.

[jackssmirkingrevenge]

I tried to build a QEV myself but I don't think i made it correctly.

If you made it as drawn with the piston rod being pulled directly by the trigger it's not exactly a QEV, closer to the QDV - but the way you built it means too much force is needed to open it.

I will answer your PM question in this thread.

The QEV/slide valve combination is perfect for a semi-auto PCP, however your desired specifications of 7mm dia 130 grain weight projectile at 700 fps plus are a little ambitious, not saying it can't be done but it will need a lot of pressure. I don't have GGDT handy (If you haven't downloaded it yet, you should ) but you're looking at a large launcher with 300-400 psi in it at least.

The only specs I found for the QEV I used in my demonstration in terms of pressure rating are ridiculously low, it's obvious that it can take a lot more safely and personally I would be comfortable putting 500 psi into it.

If you want a multishot, find yourself a high pressure source. There are plenty of options, paintball bottles, stirrup pumps, fridge compressorts... it depends on your budget and technical abilities/facilities.

[MisterDoctor]

Ok, I guess I have nothing to lose. I'll order said QEV, test it, and get back to you.

[jackssmirkingrevenge]

Ok, I guess I have nothing to lose. I'll order said QEV, test it, and get back to you.

If you're in the US, note my comments about BSP and NPT threads.

[evanmcorleytv]

Ok, I guess I have nothing to lose. I'll order said QEV, test it, and get back to you.

If you're in the US, note my comments about BSP and NPT threads.

YES. If you are in the US, buy the QEV that I showed you in my previous post.

[MisterDoctor]

If you're in the US, note my comments about BSP and NPT threads.

YES. If you are in the US, buy the QEV that I showed you in my previous post.

It's only 1/4". Is that even going to work? I would think it's going to bottleneck.

[evanmcorleytv]

If you're in the US, note my comments about BSP and NPT threads.

YES. If you are in the US, buy the QEV that I showed you in my previous post.

It's only 1/4". Is that even going to work? I would think it's going to bottleneck.

With an appropriately sized chamber, it will do JUST fine. If you wont to overkill, then use this one:

http://www.ebay.com/itm/Pneumatic-Quick ... 376wt_1110

AND if you want it to have a better, and faster rate of power, then use a 3-way valve for the pilot, like this one:

http://www.spudtech.com/store/index.php ... ucts_id=79

[jackssmirkingrevenge]

It's only 1/4". Is that even going to work? I would think it's going to bottleneck.

Most fittings have bigger internal diameters than the nominal one, all the 1/4" fittings I have are at least 8mm ID.

On the other hand, going to a 1/2" valve will give better performance, the barrel will choke the flow but air will be fed at a faster rate than the 1/4" valve.

if you want it to have a better, and faster rate of power, then use a 3-way valve for the pilot

A slide valve is a 3 way valve...