12 gauge air cartridge

[jackssmirkingrevenge]

Following on from my air cartridge for a flare gun  I've been playing with something more compact that will fit a 12 gauge shotgun.  Here is roughly what it looks like internally:



This is just a proof of concept, the idea was to have a balanced spool (orange) within the chamber that retains pressure, in this case filled through a butane lighter type valve (brown).  Because the spool diameters are balanced, it remains static.  When fired, the shotgun firing pin strikes the base pin (red) that moves the piston forward, allowing air to enter behind the piston, unbalancing it and forcing it to open.  The retaining rod (yellow) prevents the piston from blowing out.  The front of the cartridge (green) that houses the projectile is cut from a spent 12 gauge shell.

Here is some quick testing at around 1500 psi:



It certainly works, but many elements are less than ideal.

Having the front o-ring in the path of the airflow will tend to blow it out.  In my previous cartridges with the piston moving to the rear, this was not an issue.

The retaining rod takes quite a beating, I made it from brass and it started to bend from the first shot.

Just to get an idea of ballistic performance, I loaded 9 x 0.177 steel BBs, I didn't have a wad handy so I used a stack of cardboard disks instead.  From the footage these obviously blew out before the BBs so naturally a lot of energy was lost but it was still promising.

Here are the component parts and the assembled cartridge:





I don't think I will develop this exact design further as there are some fundamental issues that are not feasible to solve, but it was still a reasonable and encouraging result.

[Mr.P]

Very cool stuff thanks for sharing the details

[sb327]

Very cool. I appreciate you sharing your work here.

Dave

[JuryRigger]

Too cool!
I'm fascinated by your air cartridge ideas Jack-keep up the good work!
Jesse