The Danish Forsøgsrekylgevær (Self Loading rifle M.1888) is a fascinating early autoloading rifle. I learnt about the rifle when Ian @ TheHighRoad posted this photo and asked if anyone could identify the rifle:

Click to expand.

I could not figure out what was going on in that complex mechanism. The general consensus was that it must be some type of complex lever action until Wes Janson figured it out.

Click to expand. Photo from Statens Forsvarshistoriske Museum

The Forsøgsrekylgevær was designed by Rustmester Rasmussen (Bjarnov) and Captain VHO Madsen. What is unqiue about this rifle is that the magazine is gravity fed. You could simply pop in cartridges into the loading/magazine-like device and let gravity do the rest.

While gravity fed magazines were not uncommon and were used in Maxim, Gardener and other pre-machine-gun guns, unlike those which were very heavy and either crew served or mounted on the deck of a ship, this was designed as a infantry rifle!

Can you imagine running around in a gun fight knowing that your rifle could fail to feed, or worse, jam if you did not keep it upright? That would not have been much fun. I reckon this was why only 50 were ever made and they only saw limited service by the coast guard.
The The Danish Arms & Armor Society describe the action (translated using Google, emphasis mine):

The mechanism of rekylgeværet is a kind of automatic version of the Peabody vippende bottom piece. Instead of traditional gun magazine had a solid loading device when the cartridge collars were in the two grooves. Cartridges were to fall into the gun by their own weight. When the gun was not in use, was loading device folded down so that it covered include opening.

Gun can be used both as individual leaves and machine. By simply placed cartridge directly into the bottom piece cartridge bearing. As a machine left by loading device.

Click to expand. Photo from The Danish Arms & Armour Society (I think)

The M.1888 fired the 8x58RD cartridge. The blackpowder military load for the 8x58RD sent a 226 grain bullet @ 1591 fps generating 1270 ft/lbs of energy. The smokeless version pushed the 226 grain projectile at 2034 ft/s generating 2076 ft/lbs.

While the rifle itself has faded into obscurity the 1882 Madsen machine gun was based on its design. The Madsen was in active use for over 100 years until last year when the Brazilian police force finally retired it.

1882 Madsen machine gun replica.