I've swapped and modified and tinkered, and have finally got this gun the way I'd like it.
Even with the shorter chamber, it's quite a chore getting this thing to 300 PSI, much less the originally planned 400 PSI. However, despite the reduced pressure, it still packs a big punch (in a small package!). Here's the updated damage video, in which I make it rain.
Overall, I'm very happy with the final product. Tell me what you think!
Chamber: 1x18" type L copper
Barrel: 3/4x48" type L copper (ID 0.785")
Valve: barrel sealing piston valve with floating o-ring piston
Pilot: 1/4" ball valve
Operating pressure: 300 PSI
Check for the updated pictures at the bottom of the post.
EDIT: They're above now.
Well, I think it's just about time I post this thing.
I've had the "shell" of this launcher (the copper pipe and fittings soldered together) for nearly two years. I'd always stare at it in my closet, just waiting for an opportunity to fix it. Finally got an opportunity for Mardi Gras break, so here it is.
- Chamber: 48" of 1" type L copper pipe
- Barrel: 72" of 3/4" type L copper pipe (0.785" ID)
- Operating pressure: 200 PSI, hopefully more later
HP-1 is supposed to stand for "High Pressure" model 1, or HEAL imPersonator model1... whichever you'd like. If you don't get the other part of the name you need to start reading some Tolkien.
I originally planned to take this launcher to 450 PSI with a homemade pump. The pump works fine, but even when initially filling to ~120 PSI with a cheap bike pump, and then "topping it off" with the homemade HP pump, it takes way too long to get the launcher even to 200 PSI. It's not very enjoyable, and by the time I shoot I can barely hold the barrel steady. Future modifications would include either cutting down the chamber or investing in a HPA tank and regulator.
The valve is a 3/4" porting barrel sealing piston valve. The piston was, overall, the most tedious to assemble part of the launcher, required about a full day to get right. The first piston I built was slightly too short, which caused the piston to jam against the barrel port. After re-polishing the barrel seat, I remedied this by moving the nylon "plug" back slightly, so it would stay in the piston track.
The piston is a one-way floating o-ring type, which allows air to flow from the pilot to the chamber (when filling the pilot pressure is higher than the chamber pressure, forcing the o-ring towards the front of the piston and uncovering the equalization (blind) hole. When piloting, the pressure in the chamber is higher, forcing the o-ring towards the back of the piston, and sealing off the pilot from the chamber completely. All of this was made with standard parts (different sized washers), and the o-ring grooves simply required a couple of wraps of teflon tape to get the piston sealing in the track pipe.
Today, I got some high durometer (70A) rubber for the sealing face, and I haven't had a single leak since.
This valve will pilot with a schrader valve, which is eventually one of the reasons I switched to an auto plug and check valve for filling.
The pilot has changed a lot as well. It originally was a blowgun, but I swapped this out with a simple 1/4" ball valve mounted in a trigger's normal location. The hosing from the piston valve to the pilot valve originally was 1/4" OD copper tubing, but this turned out to inhibit my servicing the piston. I picked up a 12" length of braided stainless hose with 1/4" compression fittings at the ends, which allow for quick and reliable connections and disconnection.
Filling is accomplished through a male auto plug and a check valve.
Ergonomics (Frilly Junk)
The position of the pilot valve and the addition of a short (~10" long) shoulder stock make this thing very comfortable to shoot, even with a 7' overall length. It lends itself better to a sitting position over prone or standing, which is fine by me anyway since I usually shoot from sitting with regular firearms or airguns.
I also added a BSA red dot sight I've had laying around for years. I just had to get a new battery and it works fine. The launcher itself isn't very accurate with my current ammunition, so the best I could do was bore-sight the scope, which allows me to hit aluminum cans all day at 10 meters.
The barrel is breech loading, and slides back and forth through some 1" steel pipe nipples lined with felt.
I haven't done much filming, so I'll have to post these low pressure shots (at 160 PSI) for now. Break ends today, so the 200+ PSI shots will have to wait.
That's about all. Feel free to ask any questions as I know there's a lot of "junk" crammed into a very small space. If you have any ideas for cheap targets as well, I'll try to do some more filming after classes over the next week or two.
Here come the pictures! As always with the uploader, I can only pray these show up in the right order...
EDIT: go die in a fire, uploader. Pictures are in reverse order.
EDIT2: We uploader now.