Ball Valve Airgun

[theairgunman]

Alright, I had to build another one after using ball valves only as pilots for a couple years. It has a 8.5" air chamber made from 1/2" type M copper pipe. The barrel is made from the same pipe and it is 40" long. I have yet to build the stock and trigger system, but I do have the wood and spring for both. Firing it by hand is fun, it is really quiet. In fact, I think the typical silenced firearm would be louder. I've tested it up to 400 psi, the max of my new shock pump. It takes a whopping 77 pumps to get it up to that pressure! Yeah, you can get more power from pneumatic valves, but I like the simplicity of the good old triggered ball valve. I'll post some pics when I get the stock and trigger done. It looks like a promising coyote hunter...

[Pellethuntr]

 What exactly is a shock pump and where can I get one?

[theairgunman]

A shock pump is originally designed to adjust the suspension on really nice mountain bikes. They are high pressure low volume pumps. Here is the one I just bought: http://www.pricepoint.com/detail/16246-318_SET357-2-Accessories-37-Pumps/Sette-Air-2-ST-35-Universal-Shock-Pump.htm. I highly recommend this place, they were very quick to get my order out. Be prepared to work out, it takes a lot of strokes to get up to pressure!

[Pellethuntr]

 Cool and it's cheap!!! How did you get it to pump up you're gun? I can't figure out what I would need to plug it into?

[theairgunman]

I used a high pressure schrader valve. The real nice thing about that pump is you lose almost no air when you disconnect it, unlike the usual bike pump. I attached a picture of what I have done so far. I still need to cut the barrel down to 24", finish the stock up, and build a trigger. If I used an airgun arrow with a folding broadhead, it should bring down a deer.

[Pellethuntr]

 Yeah it would but I don't think that's legal ANYWHERE!!!

[theairgunman]

It is actually legal in my state (MO), last year was the first season open for deer hunting with airguns. In fact the first ever was taken by a kid! http://missouriconservationnews.blogspot.com/2008/10/possible-first-ever-missouri-deer-taken.html They have to be at least .40 caliber and powered by an external source like CO2, an air tank, or high pressure pump. Talk about being lucky!  I just hope I can get time off work this deer season to bring one down myself. It would be awesome to be the first to take one down with an airgun made from commonly available parts instead of a $500+ airgun. lol I'm not sure I would want too many people to know about it though...

[Pellethuntr]

 I meant the arrow! I don't think that is legal it would be considered a speargun I believe?

[theairgunman]

I'm not sure with the arrow. I talked to a conservation agent about it in '06 and he was very interested in the concept and was going to let me try it that deer season. Then I got married and moved to Texas. Now we've moved back to MO, so I'll have to see what I can do. 

I got a crude trigger system worked out. It opens fast but looks like crap. I videoed it and it literally goes from full shut to full open in one frame. At 30 frames per second, I know the valve is opening in at least 33 ms. It very well could be faster. I can hardly wait to chrony it! I'll probably chrony it before I cut the barrel down just to see the max power I can get from a 40" barrel! Now I just need to make the trigger system ride inside the stock so it will look better. Looks like I'll need some more wood and redo the whole stock.  Here is a picture:

[theairgunman]

Alright, I think I have a idea to make this trigger from just working to being great. I'll have to get two thinner pieces of wood for the outer part of the stock and a thicker piece for the inner part. The spring will ride in a gap between the thinner pieces in the forearm. A slot will be cut on both sides. The slots will need to be lined with a thin metal strip to prevent wear. On one side the ball valve will connect to the spring by means of a bolt that slides in the slot. The other side will have a cocking handle to make the gun easier to cock. That 5 lb spring is a chore to cock by hand. The trigger/sear will catch the bolt instead of a piece of pipe hanger. The system I have now has a surprisingly good pull to it. My new design should be easier to tune. Instead of using pipe hanger to attach the gun to the stock, I'm thinking of soldering a couple nuts to the gun so I can bolt the stock right to it. This will make everything more secure and hopefully as accurate as this smoothbore will get. I've got a day and a half off of work, hopefully I can get it built and maybe even chronied.

[Pellethuntr]

 Nice sounds like a interesting idea can't wait for the numbers!

[theairgunman]

Got called into work today  Guess my stock and trigger system will have to wait until Friday.

[Pellethuntr]

 Ahhh man that is tragic!!! uhhhhh frustrating ay?

[theairgunman]

I finally got to chrony my airgun today in the trim you see a few posts above. With the 40" barrel, it shoots a 40 grain marble at 518 feet per second on a 350 psi fill. That's about 24 fpe, enough to have fun with. On the downside, it looks like my ball valve only has an efficiency of 39.26%. Using these figures, GGDT says the airgun will shoot a 130 grain ball bearing at 376 fps. Not quite the performance I was hoping for as I intended to cut the barrel down to 24"  A 182 lead RB will shoot 337 fps, or 46 fpe. If I could build a 10" to 18" bolt with a folding broadhead and keep it around 182 grains, I'll be in business for deer season.
I got the new stock rough cut last night. I've got a few technical difficulties to get over before I put everything together. Hopefully I can overcome some friction losses and speed the valve up a bit for a bit more power...

[theairgunman]

I'm finally getting somewhere in my spare time! The trigger mechanism works like a charm, the sear needs a little polishing to improve the pull, but it isn't too bad! I now just need to shape the forearm, sand it down, stain it, paint the action, and attach it to the stock. It also needs a cocking handle, that spring is still a bugger without one. This new action gives a bit more spring tension, so the valve should open even faster now. That hopefully will mean more power. I cut the barrel down to 26" to make everything look proportioned.