SpudFiles

to coin a phrase, "It's a High Pressure Rifle So simple a Caveman could build it"...

I basicaslly wanted a shoulder fired version of the mini modgun that would enable heavier and larger bore projectiles to be launched using hipressure/lowvolume with performance exceeding hivvolume/low pressure pvc chambered cannons, and It works very well in that aspect, It is only about 10% down on performance from DD1 and it's 10ft barrel when I use a 36" barrel on it..

No barrel is shown in the pic, but it has a complete parts list in the pic...

It'll use any of my mini modgun barrels, as well as a 1 1/4"x36" barrel I made for it, a GB barrel I made for it, a TB barrel I made for it...

I've shot it prolly 100+ times with 750psi, and even with 6oz projectiles in the 1 1/4" PVC barrel, the barrel survives fine(but only because the barrel pressure doesn't rise fast enough to be beyond safety limits)...

With the GB barrel(36"of sdr21) I'm chronying at 720+fps..

TB barrel(28") is around 480fps...


I DO NOT recommend using PLASTIC CAMLOCKS, And would be careful with pvc barrels( depending on the diameter of the barrel the projectile only has to move a few inches to prevent catastrophic barrel failure, but if it jams before that, it could get ugly)....

nice but I think you could choose a more compact design (i.e. the main valve closer to your shoulder, thus allowing for barrel length for the same overall length)

POLAND_SPUD wrote:nice but I think you could choose a more compact design (i.e. the main valve closer to your shoulder, thus allowing for barrel length for the same overall length)

That one is in the works... It'll use copper construction and a cable actuated bv to pilot it... This was meant to be cheap, easy, and a means to test hipress/lowvolume/smallish porting with larger diameter barrels and heavier projectiles without putting undo recoil stress on elbows or tees...

Besides, do you want a pvc barrel beside YOUR head when you are slamming 750psi into it???

As a Note on price and assembly time:
3/4" qev $20
1/2" ballvalve $6
3/4" ally camlock $8
1/4"ballvalve $5
nipples and ftgs $18
-------------------------
Total cost, w/o barrel= $57, Time to assemble 15 minutes Max....

For a 750+psi capable cannon, not a bad investment, plus it shows that It doesn't take rocket science or major fabrication skills to build a VERY Powerful Launcher...

This was meant to be cheap, easy

ohh I see... I've built lots of such guns in the past... they give you the most fun out of spudding

but I prefer to have the QEV exhaust port at 90 deg to the barrel... normally I just use a T to join them: one port of the T is attached to the barrel one to the QEV and the one facing the shoulder is where I screw in a blocked off nipple... then I attached another T there to serve as a buttstock

in this way the recoil acts directly on your shoulder.. piloitng might not be as comfortable as in your design but I think that I'll buy a small QEV to assist piloting so that I could put the trigger where I want to and I advise you to do the same

pvc barrel beside YOUR head

I have to admit that I used a DWV barrel on a similar gun (but only 1/2" porting, 1.5" barrel @ 500 psi)

but a couple of days ago I found a some 1" aluminium tubes and they are really really light.. have you considered switching to alu ? I know it might be difficult to find alu tubes in larger sizes and cheap enough but they would be ideal for a gun like this

I've never been a big fan of bends in barrels... I am going to modify slightly to reduce wasted pilot volume by switching to a male run tee off the qev, and a male fitted bv... will reduce the pilot volume about an inch^3

I think you just called me a caveman...

Brian the brain wrote:I think you just called me a caveman...

Maybe

Where does the pilot vent to atmosphere on yours? through the stock?

Looks very cool for its simplicity but I think you could cut down on pilot volume if you wanted to squeeze more power out.

jor2daje wrote:Looks very cool for its simplicity but I think you could cut down on pilot volume if you wanted to squeeze more power out.

jeepkahn wrote:I am going to modify slightly to reduce wasted pilot volume by switching to a male run tee off the qev, and a male fitted bv... will reduce the pilot volume about an inch^3

Needing more power is not an issue, and using the 1/2" fullport bv trigger it vents as fast if not faster than a blowgun/.25qev combo(one of the reasons i went to bv pilot)... my main reasoning for reducing pilot volume is waste of co2, at 750psi 1"^3 of co2 is huge waste... (even though I have 50lb,20lb,5lb, and 2x 24oz pb bottles)

than a blowgun/.25qev combo

did you fill it via the blowgun or did you use a T?

also what air hose did you use (diam.), somehow I can't believe that a 1/4" qev couldn't vent faster than 1/2" bv

filled via a tee...

A .25" qev at full open will only flow about 45% of a .25" full port bv, and on that you have to add the time it takes to squeeze the blowgun trigger. With the .5" bv by the time you move the lever the same distance as the throw on the blowgun lever the .5" bv is already flowing more than the .25" qev that would just then be getting the signal to start opening...

A qev does OPEN faster than a BV, BUT, when you add the time for squeezing the trigger on the blowgun and the time for the qev to react to the pressure differential a larger ported BV is alread outflowing the smaller COMBINATION of blowgun/qev... Everybody thinks in valve opening time, but they fail to take into account the operators triggering time... And I also need to clarify that as a primary valve, a qev blowgun is faster, but when you add an extra pilot volume(between the trigger and pilot qev) you are stacking differentials which slows both valves down(because most qevs require a 2%-10% differential to react...

well yeah that's the reason why I prefer to have the QEV at 90 deg to the barrel..
since the pilot side of the QEV isn't used to support the rest of the gun & to transfer recoil to your shoulder it doesn't have to use large fittings with large internal volume... normally I just use QEV -> reduction nipple (1/2" to 1/8") -> pilot valve (1/8" DCV - acording ot its datasheet it has 280 l/m flow)


if you measure the exact volume of that setup by filling it with water I am sure you'll be surprised how large it is... I was thinking about directly attaching the piloting QEV on the main QEV and then using push-to-connect fittings and 4X2mm tubing to connect it to the pilot valve

IIRC european 1/8 QEVs have flow close to 700 l/m and from my experience that kind of flow is an overkill for 1/2" QEVs and probably will work well on 3/4" QEVs

EDIT
I found the data sheet on them -> here flow of 1/8" is higher then 700 l/m

the reason why your setup failed was becasue there was too much extra dead space both between the two QEVs and teh auxiliary qev and its pilot valve

but they fail to take into account the operators triggering time

well, I partly agree with it and I don't
from my experience people mostly think in terms of flow but they fail to take the opening time (which is equal to operators triggering time on direct acting valves (both direct acting DCVs and common valves such as a blowgun))

in theory, with a main QEV + axillary QEV combo the problem of valve opening time/operators triggering time becomes irrelevant as the valve which pilots the main QEV, that is the auxiliary QEV opens in a couple of ms

Where does the pilot vent to atmosphere on yours? through the stock?

Let me explain a real cavemen gun
There is a ballvalve on top, connecting the stock to the piston valve.Opening this valve fills the gun from the pressure stored in the stock.

Opening the bottom ( red bent handle) vents the pilot.
Opening the top one refilled the gun.
Pressure dropped with every shot..if only I had a regulator..

But this was before one of my tribe members discovered fire....

I've been around for a long, long time...

POLAND_SPUD wrote: if you measure the exact volume of that setup by filling it with water I am sure you'll be surprised how large it is...(I'm actually well aware of it) I was thinking about directly attaching the piloting QEV on the main QEV and then using push-to-connect fittings and 4X2mm tubing to connect it to the pilot valve

When I use dual qevs, I use a 1/4 attached directly to a 3/4 with a blowgun attached directly to the 1/4 qev via 1/4 tee with a filler nipple on the third leg...

poland_spud wrote:the reason why your setup failed was becasue there was too much extra dead space both between the two QEVs and teh auxiliary qev and its pilot valve

My setup never failed and is plenty fast enough,(without breaking it down to ms's via expensive timing devices) it fires as if it were a firearm(the projectile is clear of the muzzle before the trigger finger is fully contracted) there is no "hisssssbang", there's just a bang...

BUT, my rerasoning for this method of triggering is more to do with ergonomics/aesthetics than performance gains(which are arguable apparently..lol)...

But seriously, performance wise, what do you think flows more volume??? A modded blowgun or a .5"bv??? And how much finger movemnt is required for a .5"bv to exceed the flow rate of the modded blowgun... Because that's where the performance of the bv comes from when used as a pilot, amount of effort to exhaust the pilot volume between the manual valve and the qev....

nothing can compete with a qev for opening time, but there are more than one effective way to vent the trigger volume...


And For BTB: I can see a 6 port manifold with 5bv's (on the <5> chambers' side) in your future for 5 shots with equal performace....

But seriously, performance wise, what do you think flows more volume??? A modded blowgun or a .5"bv???

a 1/4" qev

why would you want to compare a 1/2" bv to a modded blowgun ? the question was whether it's better to have a 1/4" QEVs as the piloting valve or a 1/2" BV

piloting valves are similar to main valves... in both cases you have to dump air fast... I'd rather have a 1/4" QEv for the main valve not a 1/2" BV

if a 1/2" BV was superior to 1/4" QEV no one would bother to use them...


I can understand why you use a BV there, as I use them myself from time to time on single shot guns, but that doesn't mean that it a better piloting valve than 1/4" QEV as far as performance is concerned (as well as a couple of other things)