Molasses is correct, the half cock position is for loading.
The whole process is as follows.
With the revolver empty, pull the hammer to half cock. Open the loading gate, and turn the cylinder to load cartridges, just like the SAA Colt. The inside part of the cartridge rims will rest on a ring that is part of the frame.
Close the loading gate and the gun is ready to fire.
On firing some or all of the cartridges, again put the hammer on half cock, press up or back (depending on the model) on the barrel release, and turn the barrel clockwise (as seen from the back).
Pull the barrel forward away from the cylinder. If the cartridge cases are the right length, empty cases will fall away (the cylinder might have to be turned manually) while loaded rounds will be held in the cylinder by the bullet. This was the big selling point for the M&H, that it could "tell" which rounds had been fired. That was why M&H had their own line of cartridges; same caliber S&W cartridges will load and fire, but the case length is wrong.
There is another lever on the barrel; pressing it allows the barrel to be pulled completely off the cylinder arbor. Be careful; when the barrel is pulled away from the cylinder arbor, nothing holds the cylinder to the barrel and it can fall off and be damaged.
The M&H guns are very interesting, and pretty well made. They were made by Hopkins and Allen, and the H&A name is on the barrel while the M&H marking is on the side. But in spite of the supposed advantages, they were not big sellers and production ended around 1890. H&A went out of business during WWI.
Coyote, the Army models are pretty steep, but the small .38 and .32 are pretty reasonable. A few months ago, I got a near-new nickel plated .32 DA with the folding hammer spur for $450 (like the bottom one in Molasses' picture), and a .38 SA in so-so nickel for $300. Both fully functional. I also have several I paid less for but that was some time ago.
Jim
