The Full-Auto Lever-Gun

According to Wiki, a prototype of this rifle, using the first gas-operated action in history, was made in 1889.
Later, in '92 the design was patented by it's designers, the brothers Browning of Ogden, Territory of Utah.
The patent was then sold to Colt who, several years later, used the design to good effect in the Colt "Potato Digger" and so on...
As you can see, this thing is simplicity itself.
Essentially, it's a standard lever action, but with no trigger guard, a larger trigger and a shortened cocking lever linked to a rod which runs the length of the barrel.
Up at the muzzle we see the "gas-operating" principle with its pants down.
The little... flapper, I guess. The Brownings called it something different but it's buried in the copy somewhere. And I'm lazy.
Anyway, after the bullet passes through the the flapper, a convenient hole being made for the purpose, the expanding gases build up under the concave underside of the flapper and violently shove it out of the way.
It flies back on its pivot point, compressing a flat spring.
The same motion pulls the cocking linkage forward.
Then, spring pushes back, the flapper goes back to the front of the muzzle the cocking linkage is shoved back - all the way back - back to where the hinge of the linkage bears against the trigger - that's why it's so long - and fires it again.
The prototype, in .44 was said to have fired sixteen rounds in less than a second.
I see no reason why this couldn't be an after-market product.
Once the geeks worked out the arcana, weights of the flapper vs spring tension, that kind of stuff, the rest could be done in your basement.
Navy Arms ought to look into this.

We can't quit there.
Another project, perfect for our home-handyman:
The Charleton Automatic Rifle (read - Retro-fitted SMLE).
Again, these are accessories we could use.
Oh, Browning's patent and prose accompanying same is available here, Google Patents.

Further ATF (after the fact, duh):
Another, if not better - at least differently bad, photo of a Charlton rifle.
PS Click on the above to see full length.