SpudFiles

This uses the same barrel/ bolt action loading mechanism as my Bolt Action Marshmallow Rifle (http://www.spudfiles.com/forums/bolt-ac ... t8619.html)

This is my first fully functional pneumatic gun that uses pressurized air.
It is constructed using pressure rated PVC pipes and fittings, a modified sprinkler valve, and an airsoft red dot scope.

The chamber volume is 152 cubic inches.
The C:B ratio is about 18:1

I have only fired small marshmallows using this gun.
I have fired marshmallows using a chamber pressure of up to 140 psi. (sorry no chrono, but they are fast.)
I have fired up to 20 marshmallows at once, firing multiple marshmallows doesn't perceivably lower the projectile speed. They spray like a shot gun.
8)
If the marshmallows are fired perpendicular to the target, usually a fence, they flatten upon impact. If they are fired at an angle to the fence or ground, the marshmallows get skid marks on one side of them. Sometimes the marshmallows tear apart if they hit at the right angle.
Marshmallows behave strangely at high velocities. They don't always follow a ballistic path, they commonly follow a loose spiral, or follow a straight path, then shoot off at a slight angle part way through their path.
My best explanation for the strange projectile behavior is wind interference (even though it dosn't seem to be windy, it wouldn't take much)

Nice design, you obviously did your research.

I like the trigger valve, very unique and seems functional as long as it vents the pilot quickly enough.

Since you used colored primer (and, no offense, not the cleanest job) I'd suggest painting it. With a nice paint job and perhaps some handles, this gun would be quite high quality.

The scope has to be nearly useless with marshmallows... but with more aerodynamic projectiles (Think darts) it could be very useful.

Awesome first "real" pneumatic. Hope to see more from you.

Peace,
Pete Zaria.

Thats very nice, i love the scope setup and the breech loader, you also have very good ideas for the setup of the gun. The only thing is the dead space between the sprinkler valve and the projectile which will reduce performance by a small amount.

Really cool gun, but why marshmallows? Try marbles and darts and other fun (destructive) stuff!
Marco321, dead space is not a factor that destroys the performance of cannons much, unless there is a huge amount. Two little dinky elbows. Not a big deal, especially when the chamber is that big, and has enough air to "waste."

What? If I say the word "dink," in any context, it comes up with the smiley?
Testing:
basoidfohbadinkahuasdinkasdifn
Didn't work, hmmmmm...

Yeah, that big blue splotch on the chamber. I totally felt stupid when I got the coupling on, I misjudged how much I needed.

What type of paint works best on PVC?

The scope is 100% useless at 140 PSI. Around 60 or 70 PSI the projectile almost always hits somewhere in the sight window, but not on the cross hairs.

The trigger vents the pilot surprisingly quickly, it doesn't do it quite as fast as a traditional blowgun, but the airflow isn't really constricted until it hits the nozzle which has been removed.

Thanks for the input

Edit: @Marco, I approximated the volume of the dead space on this gun at about 2.4 cubic inches.

@ noname, I've only used marshmallows because I've got not open fields close enough to test in that I can haul my compressor to. I want to fire both marbles and AA batteries, and I will update you when I get the opportunity.

Oh ok thanks noname

Jumpin Jehosaphat, i think im gonna borrow your idea for the scope mount, i've never seen one like that before.

EDIT: Oh ok, i wasn't sure, i obviously misunderstood the affects of deadspace

Once again i like your ideas

The biggest problem with the scope mount is it leaves the scope far from the gun unless you trim the fittings down, I lowered it alot for this gun, but you can check out my earlier version of the gun using the link above. The scope was a couple inches from the gun there.

That's a really cool gun, I like the muzzle brake.

u blocked off the stock from the barrel right??and teh tee that the scope is on??

One would hope so, spudthug, one would hope so.

A little paint can help the purple streaking, but other than that the gun looks great. Krylon fusion paint works great. If your looking to just brush over the purple messiness, go for a model paint or any paint that bonds with plastics.

sweet gun chap, i love the rail il havto try that
and i reckon you could shoot marbles just shoot it straight up

Nice gun... sure the primer might be a little messy, but I don't think it hurts the look of the gun.

Usually I don't like high ratio pneumatic spudguns, but the dinky barrel actually looks good next to the big chamber

EDIT: WHOA thats weird when I say blahblahDINKblahblah it makes that smiley... good find noname... I am sure it will have many good uses .

spudthug wrote:u blocked off the stock from the barrel right??

Rofl!

Since so many people seem to like the scope mount, I will explain in detail how I made it.

Materials:
1/2" x 1/2" x 1/2" T
1" x 1" x 1/2" T (instead of 1" you can use whatever your barrel size is.
small length of 1/2" sch 40 PVC pipe.
2 small hose clamps

Steps:
1. Bore out the stops that join the two parallel sockets on both of the T joints
2. Trim down both of the T joints so that when you connect them, the scope will be however far from the barrel you want it to be.
3. Cut a straight line through the bottom edge of the 1"x 1"x 1/2" T
4. Cut the 1/2" T along its long edge (cut lengthwise) so that you cut off more than half of it.
5. File the 1/2" T smooth so that you can hold a 1/2" pipe flush against where you removed the stop.
6. Cut a small enough piece of pipe to couple the top and bottom T and cement them together.
7. Split the rest of the pipe, or however much you need in half lengthwise.
8. Cement one half of the split piece of pipe to the top T
9. Slide the scope mount over your barrel, when you get it where you want it, clamp it down.

The point of not just cementing the lower T into place is that you can completely remove the scope if you want, or you can change its position on the barrel easily. This also ensures that the scope mount will not interfere with the projectile (or as in my case the bolt action itself) as it travels down the barrel.

I too have built a marshmallow/marble gun, and can assure you that the strange marshmallow ballistics are not due to "wind interference". Because marshmallows are so lightweight and not perfectly round, if any spin is put on them they will curve tremendously. This spin is usually generated by friction with the barrel.

To sum it up: because marshmallows are so lightweight and wind resistant, even the smallest amount of spin will set them on a very curvy path.

On another note, scope is really badass.

praetorian91 wrote:To sum it up: because marshmallows are so lightweight and wind resistant, even the smallest amount of spin will set them on a very curvy path.

That makes sense, thanks for the explanation.
Since you mention you have used marshmallows as a projectile before, have you ever tried shooting a bunch at once? It looks so cool.