Updating .410 airgun

[Doug Wall]

If you can look at the exploded picture of mine, you can see how I extended the transfer port to move the piston down from the T opening. The face of the piston on mine sits at about halfway up the opening on the side of the T. This puts the O ring right below the bottom of the opening. Also, your 0.700 piston travel is excessive. On mine, travel is about 1/2 of the outlet diameter. Moving the piston back down to give the travel something more like 0.3 may get your O-ring down to something more like mine.
 

[Rob M]

i zoomed after downloading the pic.. I see a spring there.. is that to create more pressure between the TP and piston ?? i might just make another piston for now , with a sliding oring mounted further back on the piston , this way , even in forward position it seals to rear wall

[Doug Wall]

i zoomed after downloading the pic.. I see a spring there.. is that to create more pressure between the TP and piston ?? i might just make another piston for now , with a sliding oring mounted further back on the piston , this way , even in forward position it seals to rear wall

The piston in the picture isn't the final model. The current one is Delrin, with an O-ring. I'm using a very low flow of feed gas, so the spring is there to make sure that the piston homes back to a sealed position.

[Rob M]

i zoomed after downloading the pic.. I see a spring there.. is that to create more pressure between the TP and piston ?? i might just make another piston for now , with a sliding oring mounted further back on the piston , this way , even in forward position it seals to rear wall

The piston in the picture isn't the final model. The current one is Delrin, with an O-ring. I'm using a very low flow of feed gas, so the spring is there to make sure that the piston homes back to a sealed position.

yea, ill need to spend some time in the shop doing a version 2 .. ( at least for the coupler area and piston design )

[Rob M]

its Alive and working.. turns out , in my own stupidity i never checked whether or not the piston was actually long enough in the forward position to reach the other side of the TEE.. well it wasnt .. I just fired it a few times on shop air , stands to reason it should work the same and be defeaning on co2 .. We shall see.. thanks for all the replies, I dont have an oversight committee in the shop and i sometimes wish i did (-'

[Doug Wall]

I've been goofing around with the "Long Nine" again. The original vent valve trigger was a manually opened poppet type valve. with about 1/4" diameter at the poppet, it needed about 40 lbs force to open, and needed to open quickly. This meant a lever to get the force down, and a quick jerk to get it to open quickly. Not the best for trigger control.
Here's the latest iteration to remedy that. Please forgive the "cobbled together" look of this, but remember, this is a test bed gun, and I have limited machining resources. This valve relies on the gas wanting to push the valve stem out, and a trigger and sear, keeping it in. The O-ring on the high pressure side seals to the body, and around the stem. When the trigger is pulled back (sorry, single stage and not a nice two stage), the trigger sear releases the sear on the valve stem, and the valve stem pushes out from gas pressure(only about 10 lbs force at 850psi). As soon as the stem pushes out far enough (about 1/4") for the full diameter to clear the O-ring, the pressure releases, vents the back side of the QEV, and fires the gun. I've only tried a couple of shots with this, but it seems to be working. If it proves out, I'll clean up the design at some point to make it look nice and work even better

[Rob M]

so the stem pulls out of a captive oring , and this fires the gun? i had issues with mine and put it on the shelf for the same reasons u described, I basically needed to make a hammer valve system just to get the vent to happen fast enough , and in light of that i got lazy

[Doug Wall]

so the stem pulls out of a captive oring , and this fires the gun? i had issues with mine and put it on the shelf for the same reasons u described, I basically needed to make a hammer valve system just to get the vent to happen fast enough , and in light of that i got lazy

That's pretty much it. The sear on the stem stops at the "L" shaped part of the brass bracket, and the skinny part of the valve stem stays retained in the body. To reset it, you just push the stem back into place. I don't sense any lag time between the sear release and the firing.

[Rob M]

thats brillaint , very little pressure acting on the small diameter of the stem..

[Doug Wall]

I got a chance to try a few more shots with the updated trigger valve. It seems to be working well. I'm getting about 570 fps with 79 gr. slugs. That's about 57 FPE. It's doing 10 shots per fill.

[Rob M]

thats really awesome.. Im always building stuff but need to get back to the QEV bottle thing i made.. , heres what i was doing today