Trouble with Nerf Vortex Aero Howlers

[Dave92870]

This is my first post to Spudfiles. First here are the details of my air cannon:









This is a pnematic air cannon.
The valve is a Supah Valve Plus.
The air reservoir is made of 3" schedule 80 pvc and is 36" long.
The barrel is 3.5" ID made from 4" ABS that has been cut and inserted into another 4" ABS tube and is 60" long.
The round fired is a 7.5 oz 3.5" OD Nerf Vortex Aero Howler link here http://www.amazon.com/gp/product/B004XM ... d_i=507846

Problem:
When I fire the nerf howler out the barrel with more than 40 psi is comes out twirling/fapping like a fish/oscillating which is killing the range. Fired at 100 psi the oscillation is so great that it only flies 135 feet. A similar air cannon shown on youtube http://www.youtube.com/watch?v=3yc3fAC5vOI has the same barrel design and is able to fire about 840 feet at 85 psi and no visible flight problems and using a ball valve. I am not sure what could be causing this. Some possibilities are:

The 4" rounded elbow just before the barrel causing issues?
The supah valve hitting the round so hard and fast that it is distorting the nerf vortex in the tube?
Friction in the tube?

I am carefully positioning the nerf vortex in the barrel so that the fins do not exit the barrel and fall into the 4" rounded elbow. I am at a loss at this point and could use some guidance from the more experinced users on this board. I appreciate any advice you can give me.

[jrrdw]

Product Dimensions: 12.4 x 6.5 x 4.2 inches

The ammo may be to tight. Try anything that is 3.5" in diameter and see what kind of range you get.

Welcome to Spudfiles.

[Dave92870]

The 4.2 inches in the product description likely is for the packaging. The nerf howler is 3.5" OD and slides down the barrel easily. My possible friction concern is friction when sliding against the barrel wall at high speed.

[jrrdw]

Try other ammo anyway just to see, a few different things. That will tell you if it's the ammo or cannon.

[Dave92870]

Try other ammo anyway just to see, a few different things. That will tell you if it's the ammo or cannon.

I am definitely taking a look at modifying the nerf howler to stiffen up the tail and fins to force it to stay straight in the tubes. I think the shock of getting hit with the air burst from the Supah Valve and the shape of the rounded 90 degree elbow is causing the soft nerf howler tail and fins to bend and twist in the tube. The end goal of this launcher is to be an airsoft Howitzer prop for games (I know it does not look like a Howitzer now, the current configuration is just for testing) so I am stuck with using some variation of a nerf howler.

[Dave92870]

Try other ammo anyway just to see, a few different things. That will tell you if it's the ammo or cannon.

I will give it a shot, thanks.