Sneek peek of my first pistion valve gun, 4" coaxil.

Show us your pneumatic spud gun! Discuss pneumatic (compressed gas) powered potato guns and related accessories. Valve types, actuation, pipe, materials, fittings, compressors, safety, gas choices, and more.
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velocity3x
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Thu Jan 14, 2010 10:12 am

Jeeperforlife wrote:I already have a plan for this. I have a air cylinder used for cabinet doors that open to the top, they control how fast the door closes as it comes down and I can use them for how fast the gun rebounds and to keep it from coming to far back.
If recoil is a problem, why not address the recoil issue directly and make a muzzle brake to effectively reduce it before trying other remedies?
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Jeeperforlife
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Thu Jan 14, 2010 3:45 pm

Well I found out today that the guy in the next apartment over moved out. This meant I was able to do some testing. I found the recoil to be quite manageable wile fixed to the stand. Between the weight of the gun and and stand's flexibility it is much better than I thought.

Instead I turned to making some ammo for it. I made some darts out of stuff I had laying around. I really don't know much yet about finned projectiles and I am sure they are not built the best but I like them. They are 12" long and are 3/8" in diameter. The fins are made out of 1/8" thick by 5/8" wide steel flat bar. I still have to finnish a little welding and grinding on the but I am going to take them to work so I can weigh them.
I took a picture of them next to a 2 litre bottle for size comparision.

Image

Image
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jackssmirkingrevenge
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Thu Jan 14, 2010 3:49 pm

Looking good, with a suitable sabot it should be able to punch through a considerable thickness of steel plate ;)
hectmarr wrote:You have to make many weapons, because this field is long and short life
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Jeeperforlife
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Thu Jan 14, 2010 5:29 pm

jackssmirkingrevenge wrote:Looking good, with a suitable sabot it should be able to punch through a considerable thickness of steel plate ;)
I have some 2" OD foam rod for a sabot. I am looking in to heat treating the tip. Any suggestions?

I took the dart to my work and got the weight for it. I is just over 1/2 pound (.61LBS) . I put everything in GGDT and this is what it gave me for the darts.
473FPS and 2083 FT. Lbs
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psycix
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Thu Jan 14, 2010 6:58 pm

Now that's a dart!
You'd better find a good backstop, this thing will fly through a lot of stuff...
Till the day I'm dieing, I'll keep them spuddies flying, 'cause I can!

Spudfiles steam group, join!
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velocity3x
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Thu Jan 14, 2010 7:23 pm

Jeeperforlife wrote:I took the dart to my work and got the weight for it. It is just over 1/2 pound (.61LBS) . I put everything in GGDT and this is what it gave me for the darts.
473FPS and 2083 FT. Lbs
I once launched a 1.375 Ball Bearing (245 +/- gm.) from this cannon using only 100psi. The cannon and frame weigh approx 275 lbs and I weigh 220 lbs. I assure you.....it was a most unpleasant experience. The recoil was substantially less than manageable! (IMO)
Last edited by velocity3x on Fri Jan 22, 2010 8:56 pm, edited 1 time in total.
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Solar
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Thu Jan 14, 2010 8:32 pm

velocity3x wrote:
Jeeperforlife wrote:I took the dart to my work and got the weight for it. It is just over 1/2 pound (.61LBS) . I put everything in GGDT and this is what it gave me for the darts.
473FPS and 2083 FT. Lbs
I once launched a 1.375 Ball Bearing (245 +/- gm.) from this cannon using only 100psi. The cannon and frame weigh approx 275 lbs and I weigh 220 lbs. I assure you.....it was a most unpleasant experience. The recoil was substantially less than manageable! (IMO)
Really? Unmanageable? that seems strange that you can launch a 1 pound grenade from a M203 or M32 albeit at a low velocity, but they can still travel a quarter mile from a hand held device. Is it the the power of your launcher that is causing such recoil?
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velocity3x
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Thu Jan 14, 2010 8:46 pm

Solar wrote:Is it the the power of your launcher that is causing such recoil?
I don't know. I've always assumed everyone experienced that kind of excessive recoil when firing a projectile in that weight range.
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Jeeperforlife
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Thu Jan 14, 2010 11:19 pm

velocity3x wrote:
Jeeperforlife wrote:I took the dart to my work and got the weight for it. It is just over 1/2 pound (.61LBS) . I put everything in GGDT and this is what it gave me for the darts.
473FPS and 2083 FT. Lbs
I once launched a 1.375 Ball Bearing (245 +/- gm.) from this cannon using only 100psi. The cannon and frame weigh approx 275 lbs and I weigh 220 lbs. I assure you.....it was a most unpleasant experience. The recoil was substantially less than manageable! (IMO)
What was the ballistics data, FPS, and foot lbs? I am betting you have an exceptionally fast valve. The faster the acceleration the worse the recoil. As soon as it warms up I will give this a real test, then we will know for sure.

As it turns out I decided to swap out the steering stabilizer on my Jeep. The factory one is a soft Nitrogen charged shock that would give good recoil absorption and automatic but a good slow rebound.
jeepkahn
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Fri Jan 15, 2010 9:55 am

velocity3x wrote: The cannon and frame weigh approx 275 lbs and I weigh 220 lbs. I assure you.....it was a most unpleasant experience. The recoil was substantially less than manageable! (IMO)
If I had to guess, the actual recoil was managable, but the mass of the overall cannon/carrier is what made it rough... actual recoil would shove a lighter cannon/carrier back a few inches(and you would be able to arrest the momentum of the cannon, now with all the extra weight It's still only going to recoil a coupla inches, but the inertia of the 275lb carriage will be harder to stop...(and I'm sure the wheels don't help, even if they are lockers)

As a point of referance, I frequently launch 8oz and heavier projectiles from DD1 at 150psi, and 1.5lb projectiles from the hipster at 150psi, and 4oz plus projectiles from decimater at 750psi... Granted, the hipster is the only handheld out of those listed, but it is still managable...
My Cannons can be found by clicking the following link.
http://www.spudfiles.com/forums/viewtop ... tml#256896
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dewey-1
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Fri Jan 15, 2010 1:08 pm

Jeeperforlife wrote:
jackssmirkingrevenge wrote:Looking good, with a suitable sabot it should be able to punch through a considerable thickness of steel plate ;)
I have some 2" OD foam rod for a sabot. I am looking in to heat treating the tip. Any suggestions?

I took the dart to my work and got the weight for it. I is just over 1/2 pound (.61LBS) . I put everything in GGDT and this is what it gave me for the darts.
473FPS and 2083 FT. Lbs
Where is the center of gravity (CG) from nose? CG is the balancing point.
If it is at 8.5 inches or less it will be stable.

I have a suspicion that your CG is greater than 10 inches which will result in very poor flight stability due to basically the fins being way too heavy. You either have to add nose weight or reduce fin weight.

For your efforts it looks great but it appears to have very poor flight stability characteristics! I hope you can prove me wrong.

You need the center of pressure (CP) to be about 1 caliber minimum behind the CG , in your case 3/8" is the caliber. I am guessing your CP is about 9 inches.
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Jeeperforlife
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Fri Jan 15, 2010 11:38 pm

dewey-1 wrote:
Jeeperforlife wrote:
jackssmirkingrevenge wrote:Looking good, with a suitable sabot it should be able to punch through a considerable thickness of steel plate ;)
I have some 2" OD foam rod for a sabot. I am looking in to heat treating the tip. Any suggestions?

I took the dart to my work and got the weight for it. I is just over 1/2 pound (.61LBS) . I put everything in GGDT and this is what it gave me for the darts.
473FPS and 2083 FT. Lbs
Where is the center of gravity (CG) from nose? CG is the balancing point.
If it is at 8.5 inches or less it will be stable.

I have a suspicion that your CG is greater than 10 inches which will result in very poor flight stability due to basically the fins being way too heavy. You either have to add nose weight or reduce fin weight.

For your efforts it looks great but it appears to have very poor flight stability characteristics! I hope you can prove me wrong.

You need the center of pressure (CP) to be about 1 caliber minimum behind the CG , in your case 3/8" is the caliber. I am guessing your CP is about 9 inches.
I just got home and the center of gravity of the darts is exactly 8" from the tip. I tied a string at the center of gravity and spun it around. It started backwards and in about 1 revolution it flipped around on it's own and flew great. I really did not expect them to do that well as I did not do any research first. I am lucky.

Marcus
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dewey-1
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Sat Jan 16, 2010 8:33 am

jeeperforlife;

With your luck on getting that CG to CP dimensions proper on your first try, I salute you!

Better buy a lottery ticket soon with that kind of luck! :D

Looking forward to more pictures and video.

I can do a 2D/3D drawing for you and post it here.
Just need accurate fin dimenions.
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Jeeperforlife
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Sun Jan 17, 2010 10:33 am

dewey-1 wrote:jeeperforlife;

With your luck on getting that CG to CP dimensions proper on your first try, I salute you!

Better buy a lottery ticket soon with that kind of luck! :D

Looking forward to more pictures and video.

I can do a 2D/3D drawing for you and post it here.
Just need accurate fin dimenions.
A drawing would be great.

The shaft is 3/8" X 12" long
The fins are 4" long 1/8" thick, 5/8" tall. The back 1" of the fin is still a full 5/8"s
The angled part is 3 inchs long.

Thanks this is somthig I need to learn to do.
Marcus
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dewey-1
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Tue Jan 19, 2010 2:17 pm

Here are 2D and 3D drawings of your dart!
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2D-Dimensional
2D-Dimensional
jeepers-dart-2D.png (4.48 KiB) Viewed 410 times
3D-View
3D-View
jeepers-dart-3D.png (19.42 KiB) Viewed 410 times
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