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[kustomkb]

give it a Thompson SMG design

You read my mind! I already have the drum magazine designed and the materials gathered up.
The bulkiness of the sprinkler valve has been bothering me.
I had designed it so the receiver faced down, but seeing your sketch, now you have got me thinking differently...

don't worry, we're on the same side of the border

Oh, I see now, my brother in pneumatic arms.

[tigerblues28]

Could you machine a QEV and use that instead of the sprinkler valve? I think that would reduce the bulkiness and you could use some higher pressures,

just something to think about.

Looks sweet overall!

Nick

[kustomkb]

Could you machine a QEV and use that instead of the sprinkler valve?

Thanks Nick;

I've been trying to study up all I can. I've got two young boys and a major basement renovation on the go, so like I said, my spare time is extremely limited... These QEV's , DCV's and slide valves... are all new to me, It took me a while just to figure out the acronyms!

I've been sifting through the vast resource, this forum is, trying to catch up. As always, your guidance and collective wisdom is appreciated.








Not shown would be another brass dowel, the two connected by springs, to make the final curve to the receiver.
Perhaps not the best approach.


KB

[jackssmirkingrevenge]

I've been trying to study up all I can. I've got two young boys and a major basement renovation on the go, so like I said, my spare time is extremely limited... These QEV's , DCV's and slide valves... are all new to me, It took me a while just to figure out the acronyms!

I've been sifting through the vast resource, this forum is, trying to catch up. As always, your guidance and collective wisdom is appreciated.

I admire the fact that you still find time for such amusement while still shouldering your real world responsibilities.

A QEV is basically an exhaust valve, same concept as a sprinkler valve, but usually all metal and more compact.







More compact, it would fit the "Thompson" look much better.

[kustomkb]

I admire the fact that you still find time for such amusement while still shouldering your real world responsibilities

Thanks! I actually have several hobby projects on the go. So much to do, so little time.
When people see some of the things I have made, the usual response is "You have too much time on your hands"
To which I reply, "No, I just don't watch television", this isn't true, but it gives them pause to think about how much time does get squandered.

Thanks for the cut-away, very do-able for sure. I'll try to get it working with the current SSV (sprinler solenoid valve ) then work on the refinements.

I have been chosen to fulfill my civic duties as a juror, so now I have even less time...(for about two weeks)

KB

[kustomkb]

I got a coat of paint up in the basement and while that was drying....




It doesn't look much like an M1A1 yet... It did send those wooden dowels down range, quite hastily.

.

[jackssmirkingrevenge]

Coming along nicely!

It doesn't look much like an M1A1 yet... It did send those wooden dowels down range, quite hastily.

Hmmm... what if someone were to say, insert a small bolt in the head of said wooden dowels, and do a damage test... hmmm...

[kustomkb]

Hmmm... well, the wife will be taking the kids out this afternoon...

Well, not very impressive as far as damage goes;





There is not a lot of volume of air behind it and the small fittings may be restricting the flow?
I could try modding the valve as per the PDF or wait until I can find the time to build my own QEV.
PEX tubing is a close fit, I might try putting some tips on short pieces of that.

Perhaps I should try putting this tank on for fun;




Cheers,

KB

[jackssmirkingrevenge]

Hmmm... perhaps the valve is open for too short an interval? Or the pop-off pressure of the pilot is set too low...

[Gun Freak]

Well if you have that adjustable pop-off valve, you should put it on and set the pressure higher, and you'll probably get some better damage. In the long run it'd probably look a lot better to use a compact QEV in place of the sprinkler valve. You might have to play with the valve to get it working properly when filling from the chamber port like you are now, rather than the pilot port. Really nice job so far!

[kustomkb]

Thanks fella's!

For the second shot, I cranked the pop-off right down and activated it manually. I'll try the fan-dangled adjustable next, I just didn't have time to tap it the next size up.

I'll also try swapping out the push button valve for a blow gun. I think the push button may be a bit restrictive.

when filling from the chamber port like you are now, rather than the pilot port. Really nice job so far!

I was going over that in my mind and considering the best route. Maybe a disk and spring like JSR did?

Have fun!

KB

[jackssmirkingrevenge]

it's also possible that the reloading breech is absorbing too much of the energy of the gas, I don't know if you can achieve this without a major redesign but you need the minimum bolt movement, weakest spring possible to return the bolt and maximum flow.

[dart guy]

Hey this is just me but I say make some darts, ha ha, also I think that your desne would be better fitted in a , and I think this is right, a Barrett 50 cal look. But you would have to probably have to make a Thompson like mag because you wouldn't get many shots with a standard box mag, cool build.

[POLAND_SPUD]

I think it makes more sense to separate firing and loading phases so I am not a big fan of open bolt designs

Here's some food for your thought. It's a completely inverted system - loading takes place during pressurising the gun which minimizes performance loses.

[kustomkb]

it's also possible that the reloading breech is absorbing too much of the energy of the gas

It sure is! I pulled it apart to look at honing the bores a little and while checking the fits I realized I have made a shock absorber :violent1:



You can see the wear marks on the bolt. I have a very good sliding fit on both the piston portion of it and the bolt portion.
This is creating a compressed air zone like a shock absorber. If I put the piston in backwards and invert the cylinder, it falls right out. The other way and it falls out very slowly until the bolt is clear of the minor diameter, then drops.

I'll add a groove, on the small diameter, up to just shy of the tip, to relieve this pressure and see what happens.

Before I took it apart, I opened the push button valve. It had a tiny orifice. I switched to a blow gun and not much changed..


Yeah Dart Guy, I figured that too. If I can't blast through it, might as well stick in. Barrett would be cool too.

Thanks Poland Spud, for the time to create/ post your design drawing, but I am not sure I follow...


Thanks again for everybody's input. I know when a guy shows up, who hasn't paid his dues, and says "Hey everybody, help me design a cannon" it's tough to get behind him. That is why I started to build before asking questions. To show I am serious. I only just found the "useful links and information" post. I feel a bit silly for not reading more before diving in...

Cheers!!

KB

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