Newb making cannon for material testing: design advice

[AlchemyKeehan]

I work in a materials testing lab that currently uses a calibrated slingshot for firing steel BBs. The slingshot frequently needs to be recalibrated since the elastic stiffens over time, and we'd like to overcome this issue by using a pressurized gas system.

We need to fire 3/8" steel bbs for our tests, and need to have a valve and dial to regulate pressure, so that we can calibrate pressure to projectile speed (need to be able to vary speed as well).

So far reddit/r/airguns has advised the following:

k-wall 3/8th copper tube with threaded end into a solenoid valve that's connected to a paintball regulator via braided steel hose.

jacksmachiningreveng recommended a shop compressor as the pressure source although I'd like it to be a bit more portable than that.

My main questions are:

What is the best way to feed ammo to the barrel for a semi-auto system that doesn't require reloading each round?
What should I use as a source of pressure?
Do I have any less expensive options for the valve that has consistent opening?

(it may be relevant that I have access to a 3D printer and design tools (also a well equipped machine shop))

Any links or advice are appreciated!

[Gippeto]

Why the change in specs from single shot to semi auto?

Why portable?

What are you testing?

[matti]

Sounds strage that testing cannon should be portable and semiauto, also weird if materials testing lab can't afford a single solenoid valve

But sorry, that was not what you were asking, I was just pointing out maybe you should give us a little more information what you need.. Muzzle velocity, rate of fire, size limits ?

I would use a solenoid valve (or solenoid valve piloted QEV) and a small chamber that is filled with compressor or hpa bottle that has a suitable regulator (maybe palmers pursuit with paintball hpa bottle). Breech loading done with union or camlock or similar, or even quick disconnect fittings.. Semiauto is little harder, but not impossible for sure if you really need to have it.. If you want to play with numbers and pressures, test GGDT simulator for airguns.

[AlchemyKeehan]

Thanks for responding Matti and Gippeto (I'm not sure how to tag you here).

I think I can answer your questions by providing a few more details.

The company (startup) I work for produces a thin film for windshields and part of my job is to test its ability to stop windshield breakage from stone impacts. I'm currently doing this using a slingshot but it stiffens over time forcing me to recalibrate it.

The new bb shooter will be used for the same purpose, in addition to one other purpose. We'll be demonstrating the film at a few trade shows, and bringing a shop compressor to those is non-ideal (for aesthetics, noise, and overall presentation). Since we would like to bring some sort of demo for the impact resistance, I'll be building an enclosure to house everything and make it look pretty and safe.

The semi-automatic part is just for ease of use and to speed up the time it takes us to run the tests - we need to run a lot of samples to get any meaningful data.

Thanks!

[matti]

For the pressure source I would recommend Paintball HPA bottle and this: https://palmers-pursuit-shop.myshopify. ... industrial

I have that same regulator and 200bar HPA bottle with it. Works well.

If you need cheaper system, maybe some cheap 12vdc minicompressor with car battery will work, they are quite small. But it's slow..

[Gippeto]

Agree on the pressure source.

Barrel...skip copper. 4130 tubing is available in a myriad of sizes from Aircraft Spruce and Specialty...reasonably priced too.

https://www.aircraftspruce.ca/catalog/m ... ng_un1.php

Would suggest skipping the semi auto idea and fabricating a sliding breech similar to that used on the various Sam Yang big bore air rifles...



Use a qev for a valve and steel pipe for the chamber.