I was reloading 30mm GAU so I took some pictures along the way.  Here are the reloading tools that I use.  From left to right, the tools are a priming assistance tool, a depriming tool, and the priming tool shell holder.



First up is to deprime the cases.  I used the depriming tool and a hydraulic press to press the priming tube and primer out of the case.  The next step is to then seal the top of the priming tube:



Next up is filling the primer tube with black powder:



I then place a piece of tape over the end of the priming tube and trim to size.  This piece of tape is just used to hold the black powder in the priming tube while inserting the priming tube and primer into the case:




The primer tube is then inserted into the case and the primer is pressed in using the shell holder.  There's a bolt in the middle of the shell holder.  I lower the bolt which leaves a depression to center the primer for pressing the primer partway into the case.  I then remove the case, raise the bolt to final primer depth, and finish the pressing in of the primer




Next up is to find some powder and projectiles:




These projos weigh 9 ounces and I'm loading 4 ounces of powder in the case:





I used to crimp the projos into the case but now I just glue them in.  It's easier and is less reworking of the case:



The finished product:



BOOM!  (from an old video and not these exact reloads)

Very cool - thanks for posting. Incidentally, how did you come up with the proper load so that you did blow your gun and self up?

Great question and thanks for the interest.  I found some preliminary load information on the General Dynamics website but it listed different powder types and projectiles.  The Super Slow powder is pulled from a much larger cannon cartridge.  From that I assumed that it would be slower burning powder than the real 30mm powder.  I worked up to full loads by starting with a full case of black powder and then increasing the amount of Super Slow powder.  I should have gotten video of those huge smoke clouds.

My gun is significantly overbuilt for the 30mm pressures so that info and a long string on the firing lanyard made for relatively relaxed test firing.  My gunsmith buddy did hide on the other side of a large berm during the initial test firing though.  It felt a little lonely on the range for the first shot.  

What is your cost per round reloaded, and the cost of the artillery piece you built?

The reloads are around $8 each.  I didn't keep records on the gun build but best guess is $8k or so.  I could build a second one cheaper by not having to rework stuff, not using a commercial carriage kit, subbing out some of the more time consuming operations, etc

The coolest part of the build was that I knew very little about machine work prior to starting this.  My buddy taught me along the way so I consider it as including a machine operator training program

He watched me like a hawk while I was learning to make sure I didn't screw up his equipment or the jobs.  The best day of the build was when I started work on the mill and he said "you know what you're doing - I'll be outside if you need anything"

That was even better than firing the first shot

I use much the same technique for reloading my 20x102. Press primer out (mine are swaged for 50bmg primers) and put new one in with drill press. Measure out 500gr of surplus WC87x and hotglue in the projectile.

Damn that is cool. Where do you find the brass and projectiles?

They are around. CDVS.US has them but $$$. Lots of cheaper places to find them

Very nice

OK, now I'm excited to actually do something with my GAU 8 barrel.

Did you design the breech?

The 30mm breach is as simple as I could get.  It's a continuous buttress thread screw breach shell holder design.  Check out the Armament Engineering book if you have any interest in building a cannon.  It's an interesting read even if you never build anything.  Feel free to PM me if I can help.

....and post pics!