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Old 02-04-2013, 11:14 PM   #1 (permalink)
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Yar! The scruffy pirate pistol (beware of more pics!)

I'll be making thousands of these cheap, as soon as PTP builds them for me.

I was fiddling with this idea for a while. Not a whole lot you can do with a single shot marker, but the idea was to make it simple. When PTP had their garage sale, I thought I might do this for the pile-of-pooh build. All but one of the parts I ordered ended up scattered across the united states via the giant hole the USPS put in the mailer. I finally got another barrel. I really wanted to build a pair of these for dueling, but I figured I had a lot of prototyping to do in the first place. It is a low pressure (~225 psi) balanced, retreating spool valve. It is a muzzle loader.



The trigger is just a brass rod stick trigger, and the stock is a piece of 2x4. The "receiver" is a PTP automag foregrip with autococker threads with an extra 1/4" bore, and something like a 5/16" bore in the back, er top. The fill fitting is a HPA bottle check valve.





This is in the fired position



This is in the ready position



This shows the breech plug that fits in the barrel (standard cocker threads), the pointy spool, and the preload spring.



The breech plug is coned on the ball side.



These are all of the parts except for the brass trigger/sear. I fill it with an HPA bottle with an ergo reg and gauge hooked to a quick disconnect and slide check. You connect it, slide it up, slide back and disconnect. It's not very loud and shoots reballs around the bedroom very well, when the wife is not home.



The 225 psi is what I ended up with for about 280 fps in early testing. Now that I have my precision frame, I need to get some first strikes for it. There's a bodarc tree that I think will be the donor of my real stock, and I have the brass for a trigger guard.

***

Here's a better pic of the arrangement.



and the sear, dremel'ed and drilled from a piece of 1/4" brass square,



and the fill station, as it is



so, a bit of finish work left to do.
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Old 02-04-2013, 11:38 PM   #2 (permalink)
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this is awesome. I want 2 in brass (if possible ) care to post any related drawings/info not able to be gleaned from images?
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Old 02-05-2013, 10:10 AM   #3 (permalink)
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Yeeeeaah. I'm happy to post any dimensions. I'll have to admit I'm behind in the CAD department. I keep looking for something that I'm willing to invest the time into the interface. I need an old copy of autocad 12

I did a bunch of sketches on sketchbook, but made adjustments for the tooling I had available. The spool was going to be 3/8" nominal, but I bunged up my 3/8" bit years ago and it makes an oversized hole, so it is all 23/64". I'll be making a drawing though. I've already forgotten where some of the dimensions came out. Fortunately, it is a pretty tolerant design.

One reason it is laid out this way is so that you can change out the spool design. You can do an unbalanced spool by reducing the breech plug ID. I would like to get some CFD software and model the front cone and test out different shapes. With a threaded sleeve, I can go back and reduce the whole spool diameter. I checked the stresses around 300 psi and had a worst safety factor estimate of 3 (accounting for my poor machining and a silly bad fit), so it has some tinker room. The opening force can be manipulated with the internal spring and the balance of the [spool]. I wouldn't do a forward moving spool without checking the stresses because you would want to make it thinner relative to the front seal. Once you get it well above the seal friction, your velocity consistency should be only in your starting pressure and paint to bore match.

Once it's nice and consistent, this would be a lot of fun as a dueling pistol with first strike rounds. I've been studying WALZ's stocks and would like to dress up a pair. If two people brought separate pistols, I would say you trade pistols for at least the first duel, even if the FS rounds put you at good distance.
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Old 02-05-2013, 11:14 AM   #4 (permalink)
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how would you control velocity beyond just pressure?
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Old 02-05-2013, 11:48 AM   #5 (permalink)
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Originally Posted by Spider! View Post
Yeeeeaah. I'm happy to post any dimensions. I'll have to admit I'm behind in the CAD department. I keep looking for something that I'm willing to invest the time into the interface. I need an old copy of autocad 12

I did a bunch of sketches on sketchbook, but made adjustments for the tooling I had available. The spool was going to be 3/8" nominal, but I bunged up my 3/8" bit years ago and it makes an oversized hole, so it is all 23/64". I'll be making a drawing though. I've already forgotten where some of the dimensions came out. Fortunately, it is a pretty tolerant design.

One reason it is laid out this way is so that you can change out the spool design. You can do an unbalanced spool by reducing the breech plug ID. I would like to get some CFD software and model the front cone and test out different shapes. With a threaded sleeve, I can go back and reduce the whole spool diameter. I checked the stresses around 300 psi and had a worst safety factor estimate of 3 (accounting for my poor machining and a silly bad fit), so it has some tinker room. The opening force can be manipulated with the internal spring and the balance of the poppet. I wouldn't do a forward moving spool without checking the stresses because you would want to make it thinner relative to the front seal. Once you get it well above the seal friction, your velocity consistency should be only in your starting pressure and paint to bore match.

Once it's nice and consistent, this would be a lot of fun as a dueling pistol with first strike rounds. I've been studying WALZ's stocks and would like to dress up a pair. If two people brought separate pistols, I would say you trade pistols for at least the first duel, even if the FS rounds put you at good distance.
As far as CAD software goes, check out Inventor. I have the student edition and it works well enough. I can PM you my log in info if you need it, since they want you to have a .edu e-mail.
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Old 02-05-2013, 12:35 PM   #6 (permalink)
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how would you control velocity beyond just pressure?
Just pressure, it's fairly sensitive. That's why my "fill station" is an ergo reg with a little gauge on it. You fill the chamber at the set pressure and it's ready. If you were going to wander around with it, it needs a safety.

Thanks for the offer skibbo, but I'm looking for something I can use at home that will last more than a couple years without forcing me to change. I get tired of new interfaces, especially when they just get re-arranged. I deal with lots of interfaces and I don't have a lot of memory space left. I have Inventor Fusion on my work laptop, but I think it needs my work network to function. I'll give it another poke.

I'll try to get a "shooting vid" together. My neighbor was working the the back corner of his yard the other day, right behind where I like to put my test shots.
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Old 02-06-2013, 11:21 AM   #7 (permalink)
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Very clever. I don't get how it keeps from firing. Just the tension the spring loaded bar pressing against the bolt head is enough?
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Old 02-06-2013, 12:03 PM   #8 (permalink)
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I see a little notch to hold the end of the bolt.
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Old 02-06-2013, 12:07 PM   #9 (permalink)
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Very clever. I don't get how it keeps from firing. Just the tension the spring loaded bar pressing against the bolt head is enough?
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I see a little notch to hold the end of the bolt.

Yes, there is a notch in there, and two springs altogether. The spool is balanced (same front and back bores), so under pressure it doesn't want to move, especially with a little seal friction. It's a bit of a mouse trap. The [spool] spring lets you set it easily with a thumb push and pushes the spool open when the brass sear drops (which is hinged on the pin going through the stock). The [spool] spring pushes against the back of the breech plug and the big shoulder on the spool. The hump in the middle just helps keep the spring aligned (well, that's why I put it there). The bolt head is actually the sear engagement adjustment too. It lets me set the exact position for the forward seal on the spool, after the body is so carefully mounted.

I was originally going to make it un-balanced so that the spool naturally wanted to go backwards, but I didn't want my sear tension varying with my chamber pressure, which I wasn't sure what the pressure would be in the end.

The spool travel is about .2" I think. I started out to make everything 1/4" here and there with 3/8" bores, but then it all needed to fit together. The back bore is long enough that the rear seal won't clear.
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Old 02-06-2013, 01:17 PM   #10 (permalink)
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^^^ I added some pics at the bottom of #1 to show that better.
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