Semi-auto 800 PSI .51cal WIP

[JDP12]

Alright, heres a WIP thread. It's gone through many variations... but this is my final design as its very simple compared to the original.

It's based on POLAND_SPUDS Mark III- http://www.spudfiles.com/forums/semiaut ... 20259.html

Look at my diagram for the differences:

1) bullpup config, chamber just rotated forward
2) magazine fed saboted darts
3) instead of a qev as the main valve, it'll be a barrel sealing custom made piston valve. piston is machined of HDPE. Reason for this is to handle 800 PSI... its a very small piston valve, piston diameter is .74"

Barrel will be .625" ID, GGDT predicts an output of 604 ft/s and 187 ft/lb, quite satisfactory for what I'm goin for.

The piston isn't done, I haven't gotten the o-ring yet so I haven't machined the groove, but the piston was machined via Technicians how to located here- http://www.spudfiles.com/forums/tutoria ... 21740.html

QEV is the one JSR used in his semi auto thread-

http://www.ebay.com/itm/350509538710?ss ... 136wt_1139

This will be updated periodically, I'm on winter break now so things should happen fairly quickly but actual assembly won't happen for a couple weeks cuz the QEV, slide valve, air cylinder and tubing are all being shipped to my college house.

[jackssmirkingrevenge]

Good luck with it

Any details on how you plan to make and feed the saboted darts?

Unless it's a one piece sabot, you'll need... CARTRIDGES!

[JDP12]

Making darts.. right now the dart design is a 2 piece composite. The front will be made of some sort of hardened steel, whereas the fin area will probably be cast of epoxy.

As far as the sabots... I really don't wanna have to deal with cartridges. I really freakin don't..

I was thinkin 3 piece sabots (prolly balsa wood) but lightly glue them to each other (not the dart) using a light aerosol spray glue. My thinkin is the adhesive will hold it together just enough to feed, but light enough to still separate just fine due to the massive air resistance.

[jackssmirkingrevenge]

I was thinkin 3 piece sabots (prolly balsa wood) but lightly glue them to each other (not the dart) using a light aerosol spray glue. My thinkin is the adhesive will hold it together just enough to feed, but light enough to still separate just fine due to the massive air resistance.

Sounds a bit touch-and-go.

A one piece "cup" sabot sounds like it will be more reliable.

[JDP12]

yup... thats true, makes more sense, might be a little more difficult with fins.. but we'll see what we can do.

[jackssmirkingrevenge]

Well not necessarily.

Something mentioned in the long range thread: http://www.spudfiles.com/forums/viewtop ... tml#316658

[JDP12]

hmm interesting.. could work.. all the stuff at the end of the barrel seems a bit complicated.. a sabot system could be delayed and i could just use some .625" diameter projectiles for initial stuff, sabot system (and supreme accuracy) might have to be put on hold.

[POLAND_SPUD]

cool

[jackssmirkingrevenge]

all the stuff at the end of the barrel seems a bit complicated..

That wasn't really necessary, drag alone should take care of it. The proposals were just to ease MrC's fears about sabot separation.

Incidentally the same issues he seems to be having now

[JDP12]

Ok did alot of work today.

Finished the piston and put the o-ring in it, fitted a sealing face to it, and found some AWESOME endcaps that have a FLAT surface which makes drilling and tapping holes alot easier.

The piston housing is a 3/4" nipple, and has a smooth inside so there is no weld seam.

Gonna glue the nut to the bolt so theres no leakage potential, and i'm actually a little worried the piston may be a PERFECT 100% seal, so i may have to add a hole through the piston so the chamber can fill.

Gonna rep Technician's tutorial again here- works like a charm, and its SUPER easy and makes a very professional looking piston.

Tomorrow I'm hoping to fully assemble the valve, add a test chamber, and add the sealing face for the piston.

You won't actually see this gun fully assembled for a couple weeks since most of the parts are being shipped to my college house.

[Hawkeye]

Why are you surprised an o-ring gives a 100% seal? Isn't that kind of tthe point?

[Gun Freak]

Looks like there is not washer on the sealing face; adding a small one might help, if you can fit one. Not sure on your seat diameter.

[JDP12]

the nut is practically a washer, the barrel ID is .5 something inches, and the nut fits perfectly in it with almost no room to spare so i don't think i'll need one.

[jackssmirkingrevenge]

i may have to add a hole through the piston so the chamber can fill.

Why not reduce the diameter ahead of the o-ring groove and make it float:

[JDP12]

im probably going to, my original plan was for a floating o-ring, however the o-ring i have juuuuust baaaarelly holds itself in the pipe, so i wanted to stretch it a bit. but i might go to a floating o-ring we'll see. I can always go to floating o-ring at any point.