If 37mm launchers are not considered "firearms", that would mean that a full-automatic one cannot be considered a "machinegun", right?

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So, has anybody ever attempted to build a 37mm Mk19 clone? A belt-fed, fully-automatic, absolute-king-of-4th-of-July fireworks dispenser?

HA! Tagging this thread for sure. Im interested

Totally and absolutely doable.

As to why it hasn't been done: you do have a machine shop and a few tens of thousands of dollars to spare - right?

I thought about getting a Mk19 parts kit and modifying it to shoot the low velocity 40mm rounds as I have access to all kinds of machines.
I put that idea out there and a couple of people who I respect very much(Destiny and GROG) recommended against it for multiple reasons so I let that thought go.
It would be extremely cool to have a belt fed 40mm, cloth belts like a 1919.

It would. However when running the high pressure 40x53mm ammo the Mk19 is already barely functional. It genuinely exists on the edge of "this is amazing and actually works" and "well it was a good idea but it's just not going to work".

Turning it into a semi auto or changing the caliber is asking for all kinds of issues to hammer out.

You saved yourself a giant headache in my opinion.

I greatly respect the omnipotent stompers' opinion on the topic.

Here's a thought:

Instead of trying to reinvent the 19 to work with a weaker cartridge, what would happen if you based it off an electric motor? Does it matter if it is recoil / impulse operated? You just want FA 37mm flares lighting up the night sky?

While I think a 37mm rotary barrel would get me so hard I'd pass out, even a single barrel setup that sort of aped the 19 would look cool and be fun to shoot. If you have access to the machinery, all it would take is a few days at one of the homebuilt gun forums to get someone to design it.

Plus, with the lower pressures, seems like it would be safer, and not have to worry as much about the (a) barrel popping or other issues you might see with the high pressure rounds.

Most boring would be to set it up like a pyro cake / faux metalstorm, and use solenoids to fire the individual carts, like a helo rocket pod.

Don't give up, this is a cool idea.

The predecessor was crank-operated.

Might work better.

Don't forget China lake made a pump, and law enforcement has had rotary mag units, too.

Lot of room to think about honestly

That's what I was thinking.
MK18 ought to be pretty easy.

But it's crank operated and OP said he wanted full auto.
I think full auto is the point.

There are 37mm revolving launchers, usually for riot rounds.

take off the crank

add a powerwheels car motor

Todd at Ohio Rapid Fire (ORF RIP Todd....opinions of him vary but he made some products the pushed the boundaries of firearms obtainable by common folks) made an 80% Mk19 receiver, towards a semi-auto DD registerable vs full auto restricted by the 84 FPA.

What is the original Mk19 main housing made from, steel or aluminum?

Anybody ever seen a spec drawing or "blueprint" for the main housing?    I tried scaling up a 1/6 model kit but details like the corner radii are difficult to calculate from a model kit.

Big ol thick stamped and welded steel for the receiver
Very much reminds me of an M60
The Mk47 by contrast reminds me of a swiss watch, those things are impressive inside.

Mk18 handcrank is my dream!

The HD vids I been able to find look like the main housing is about 3/16" to more likely 1/4" thick,   75lb overall weight.

The bottom and top corners look like they must be 3/8" to 1/2" radius, that makes a major difference in the dimensions vs squared corners

https://en.wikipedia.org/wiki/Hotchkiss_gun

My local courthouse has two of these. The barrels are rifled and steel though, so DDs. GROG

The bolt on a Mk19 is way to heavy to operate properly with a 37mm.  That then leads to the spring tension, and a cascade of other issues that would arise trying to use a kit to build a belt fed 37.

So far as belts go, I am sure the links on the HP rounds will work, but it would be a pain in the ass trying to get them off intact, and I have never seen virgin links available.  

It seems to me from a cursory view that trying to use a kit would be a waste of money and a kit.  But making one from scratch that resembles a Mk19 on a one to one scale would be rad, and I encourage this to happen!

Mk 19 is straight blowback.  Use a lighter bolt, can run on 37mm.

More straightforward from a legal perspective would be a cranked Mk 18.