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Old 09-06-2014, 02:50 PM   #1
mwarnick1 OP
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30mm GAU Build: How I learned to stop worrying and love the gun

I posted a few pics of this gun in another thread and the folks there asked me to start a thread with more info. I think that they might have really just wanted me to get the hell out of their thread so it could stay on-topic. It's a long twisted tale but I'll post some of the highlights and if anyone's interested we'll see where it goes.

I have way too many hours, days, and years of my life into building this gun. At one point my wife was convinced that the supposed 'gun build' was just a cover story because there was no way it could take this long to build. She once made a trip to the shop with me to confirm that there actually WAS a build in progress. Over that time I've bounced back and forth between "I hate this damn thing" and "This is cool as hell"

Here's a recent picture:



Here's how it started.... In the year 2000 the Alaska Machine Gun Association was formed. This is a group of machine gun, silencer, cannon, etc collectors. Bringing this group together immediately started a localized arms race. Who could bring the coolest toy to a local shoot?

As I was surfing the web one day I found a 105mm cannon for sale. The owner was asking $15k. This is crazy money for a gun but is actually a killer price for this particular gun. It's probably at least tripled in value since then. I checked up on the gun for a few months and then one day it sold. For years I looked for other cannons to pop up for sale but none did. I had missed my chance.

About this same time I met my gunsmith buddy. He pretty much became the club gunsmith. One day he suggested I quit whining about the 105mm that got away and that we just build a cannon.

Holy crap. You mean we can do that?

The gun was based on a M3 37mm gun and started with a replica kit from these guys:

http://users.multipro.com/brentandlo...3AT%2037MM.htm

The gun was originally supposed to be built with a sliding breech which is why the receiver is so freaking huge. Over time I realized the sliding breech was way too much work so we moved to a buttress thread screw breech. This also solved the problem of reloading dies. No dies are needed since there's enough force to ram the reloaded shell into the chamber



The second reason it's so big is that when we first starting planning this, I didn't know how to run the math on the strength calculations. Eventually I got this book which taught me. Unfortunately it was after we'd already built the initial bolt so we had to rework it to a larger diameter...

http://www.amazon.com/Armament-Engin.../dp/1412002419

Trying to get anyone to talk about strength calcs, heat treating specs, cannon reloading, etc is way worse than pulling teeth. Very few people know and most of them aren't talking much. In the past 5 years there's been a surge of interest (relatively speaking). I eventually found enough of the right people to talk with and learned the secret handshakes.

I still have to laugh about cold-calling ATK and General Dynamics or showing up at their booth at SHOT to talk with them about 30mm GAU ammo and propellants. Surprisingly enough they were willing to talk and didn't hang up like I'd expected.



More to follow....
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Old 09-06-2014, 02:57 PM   #2
mwarnick1 OP
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I don't have many pics of the lathe and mill work we did. I spent so many hours on the mill that the last thing I wanted of it was pictures. I now of course which I had some.

The recoil sled and carriage work had more pictures taken since progress moved quickly enough to make it more interesting.

Here's a pic of the recoil sled showing the GoldWing shocks:



Here's another view with the receiver and barrel mounted:



Misc Carriage build pictures. This one shows the steering box used for traverse:



This one shows the car jack used for elevation:





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Old 09-06-2014, 03:00 PM   #3
mwarnick1 OP
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A couple more finished pics:





A pic of my buddy. He gets huge credit for basically designing this gun on the back of napkins:

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Old 09-06-2014, 03:08 PM   #4
mwarnick1 OP
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And here's the end result. This is the second test fire of the gun and the first test fire while on the carriage. We were sighting through the bore so the hits on the water barrel and steel are marginal. I really had hoped to nail them dead center.



The first test fire involved me standing on the range with a string in my hand. The string was attached to the firing mechanism/barrel/receiver which was resting in old car tires.

My buddy (the brains behind this operation remember) went running around the berm giggling to make sure he wasn't in the "gun blows up on the first round" zone. It felt pretty lonely when I pulled the cord for the first time!

If you're not familiar with this stuff, state and federal laws were followed. In a nutshell, if you can legally buy a pistol from a dealer then you can do something like is shown in this thread. It just takes a few hoops to jump through....

mwarnick1 screwed with this post 09-06-2014 at 03:18 PM
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Old 09-06-2014, 03:32 PM   #5
mwarnick1 OP
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As a couple of fun facts, the gun has over 120,000 ft/lbs of energy at the muzzle. It fires a ~3/4 pound projectile at around 3200 fps

mwarnick1 screwed with this post 09-06-2014 at 04:11 PM
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Old 09-06-2014, 04:06 PM   #6
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I went on a couple of shoots out in the desert with a loose affiliation of people from the Seattle area who had various cannons and mortars. Pretty much if it is muzzleloading and doesn't have an explosive projectile, you can own and fire these without NFA paperwork.

You can do cartridge cannon/mortars, if muzzle loaded and black powder - IIRC (it was 20 years ago).

Lots of fun shooting these at "long range" (1km to 2km) - IMO the mortars were more fun, but both were fun. Several people had taken various cut up barrels from tanks and such, cut off each end to make them square, then threaded them and put either a threaded breach or a welded breach on them.
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Old 09-06-2014, 04:17 PM   #7
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Originally Posted by CodeMonkee View Post
I went on a couple of shoots out in the desert with a loose affiliation of people from the Seattle area
Aren't those shoots a great time? Sharing this stuff is what makes it most fun.
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Old 09-07-2014, 03:11 AM   #8
C/1/509
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Originally Posted by mwarnick1 View Post
As a couple of fun facts, the gun has over 120,000 ft/lbs of energy at the muzzle. It fires a ~3/4 pound projectile at around 3200 fps
Are the projectiles some sort of training round? What do you use for powder?
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Old 09-07-2014, 06:13 AM   #9
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Quote:
Originally Posted by mwarnick1 View Post
As a couple of fun facts, the gun has over 120,000 ft/lbs of energy at the muzzle. It fires a ~3/4 pound projectile at around 3200 fps
mother of god...
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Old 09-07-2014, 06:35 AM   #10
mwarnick1 OP
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Originally Posted by C/1/509 View Post
Are the projectiles some sort of training round? What do you use for powder?
Yep - the projos shown in the picture are all training-practice rounds. The black ones were projectiles for (I believe) an experimental 30mm helicopter round. The blue ones are Gau-8.

Primers are hard to find but are out there. There is a initiator tube of black powder that the primer sets off. They tend to self destruct after a shot or two so I make new ones out of tubing.

The powder was initially really easy to get. There was 'Super Slow' that was for sale via the surplus powder re-sellers. It was pulled powder from large bore stuff so it was slower than I needed but worked. Once that dried it up it was hard to find. There are now a few new manufacture cannon powders out there.

The weak link is the cases. The holy grail of this gun is to get steel cases. Apparently they use steel cases in Europe on ground mounted guns where weight isn't an issue. We struck out with contacting the European armament companies. They wouldn't talk. I've never actually seen a steel GAU case in person before so it's definitely a quest for the grail. Supposedly the US made a few of them during initial trials but it was a very limited run.

To reload I just assemble everything and then gorilla glue the projectile into the fired case. No need to resize which makes it easy. The hardest part is depriming and getting the initiator tube out.

Thanks for the interest.
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Old 09-07-2014, 06:41 AM   #11
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mother of god...
This is why I was feeling so lonely while standing out on the range by myself for the first test fire. With how thick the sidewalls of the receiver are though, we could probably use this chunk of steel to make a 105mm out of.

Finding a piece of 4140 this big was another quest. I ended up having to contact the steel mills directly and it took some calls before I found one back east (Ohio maybe) that made the stuff.
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Old 09-07-2014, 06:06 PM   #12
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Way off the scale on the coolness meter. Hats off on the build.
Jim
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