Firearms oddities

==19th century designs==
The 19th century is widely acknowledged as a period of innovation across many fields. Indeed, firearms development really took off in the mid-late 19th century, with the advent of practical repeaters and revolvers. But many of the best designs were patented, and as a result, some unusual designs emerged as direct results of gunmakers attempting to evade patents. These included the poorly thought-out "turret guns" and "chain guns". Many turret guns were made as a cheap (and predictably less reliable) alternative to expensive and patented designs such as those of Colt or Adams. Turret guns were usually percussion pistols or rifles with a rotating wheel or drum. The wheel rotated horizontally rather than vertically, and as such the chambers were placed around the edges of the wheel. The chambers opened in all directions, so that if two bullets were placed in opposite chambers, they would collide, often proving fatal for the firer. Despite this, the design enjoyed very moderate success; I suspect this is likely because few of the weapons were actually ever discharged. Most turret guns were made in the first half of the 19th century, around the 1830s - 1850s.
Chain guns were a less dangerous alternative that appeared later. They were still essentially an attempt to evade revolver patents, but the idea behind them was quite clever - rather than a rotating wheel or cylinder, chain guns had (as the name suggests) a sort of chain of bullets feeding into the weapon, similar to a belt-fed machine gun. Chain guns, like turret guns, were typically designed as pistols and rifles. Most chain guns had an external chain, although examples exist in which the chain in internal. Chain guns were prone to malfunction, and no match for proven revolver designs, although the chain gun's claim to fame (at the time) was that they could chamber an absurd amount of bullets. The French Guycot chain rifle had an internal chain capacity of 100 rounds!
A more popular alternative to expensive revolvers was the "pepperbox". Pepperboxes were inexpensive percussion pistols with multiple barrels that rotated around a central axis. Typically the barrels were short and stubby, and as a result the effective range of pepperboxes was very short. They were probably intended for self-defence in urban areas, since they were designed to be concealed with ease. The pepperbox design was popular in England, and to some extent Belgium and France, but it did not stand the test of time and by the late 19th century it had been replaced by conventional pocket revolvers such as Webley's British Bulldog.
Other unusual designs were simply the product of a vivid imagination. Perhaps the most ingenious in theory, but ultimately flawed in practice, design was courtesy of Joseph Enouy of Middlesex, England. Enouy designed and patented his "compound magazine" revolver in 1855. It was a transitional percussion revolver with a large, rotating wheel that held 8 cylinders with 6 chambers each. The idea behind the weapon is a clever one - that the firer would be able to reload the weapon in a matter of seconds by simply rotating the underside wheel - but in actuality the revolver weighed an immense amount with the device attached and every chamber loaded, not to mention that it was unwieldy and impossible to holster or conceal.
===The United States of America===
The most iconic firearms of the period in the USA were undoubtedly those of Samuel Colt. Colt is often credited with inventing the revolver; this is untrue, although he did patent the design and effectively popularize it. Perhaps inspired by Colt's success, many American gunmakers patented their own designs, few of which were successful. 
An example of such is a revolver made by W.H. Philip. It is similar in appearance to a Colt or Remington pistol, but it is capable of using up to 3 cylinders - at the same time. How exactly it functioned is a bit of a mystery to me. Apparently each cylinder had seven chambers, and once the first cylinder was depleted, the cylinder behind it would begin to discharge, with the bullets going through the chambers of the first cylinder, and so on. The design was patented by Philip in 1873, but it was never a success. Hardly surprising.
Amazingly, though, Philip's revolver was not unique. Several patents from around the same period depict revolvers with two or more cylinders, such as W. Orr's patent in 1874 and G.H. Garderner's in 1865. A few were actually produced, though not in large numbers. Why anyone thought it was a viable method of increasing a revolver's ammunition capacity is beyond me.
Another American design, focused around the same idea of allowing a revolver to fire more than six shots but executing it in a completely different way, was Aaron C. Vaughan's revolver. The revolver almost perfectly replicates the appearance of a Colt design, but is much larger due to the fact that it had twin barrels and hammers. The cylinder held 14 rounds, with 7 inner chambers and 7 outer chambers. The barrels were not even; the right barrel was slightly higher than the left, so that the right barrel would fire the bullets contained in the outer chambers and the left barrel would fire the bullets in the inner chambers. No doubt the weapon would have been very hefty whilst fully loaded, and quite uncomfortable to shoot due to the large size. Needless to say, it wasn't particularly successful, although a similar concept courtesy of Dr. Alexandre LeMat was actually quite successful, and LeMat revolvers were semi-famously used by some officers in the American civil war.
==The 20th century==
By the turn of the century, the revolver had more or less been perfected and the automatic pistol was beginning to emerge, with German designs such as the Borchardt and the famous Mauser C/96 "broomhandle" revolutionizing handgun design. The first automatic pistol to come out of Great Britain was Hugh Gabbett-Fairfax's "Mars" pistol. The Mars was an enormous and overly-complex handgun that was actually designed in the late 1890's, but started production at Webley around 1901. Gabbett-Fairfax demanded that the pistol be chambered for heavy-grain ammunition, and at the time it was the most powerful handgun in the world by a long shot. However, this came at a cost - practicality. After Gabbett-Fairfax submitted the pistol for trials with the British armed forces, it was rejected due to massively excessive recoil. Infamously, the report for the Royal Navy's trial of the Mars pistol noted that "No-one who once fired the pistol wished to shoot it again...". The development of the pistol, which was funded through Gabbett-Fairfax's personal funds, bankrupted him. There was a syndicate created to market the pistol, although Gabbett-Fairfax was not among the members of this syndicate, and it was ultimately unsuccessful.
Spurred by experiences in the Boer Wars in which the South African Boers would deploy Mauser carbines on horseback against the British forces, the British Army felt it needed a short rifle or carbine for service. In response to their interest in carbines, James Baird Thorneycroft of Ayrshire, Scotland created a short bolt-action rifle in 1901 which had the same barrel length as the Lee-Enfield, but a much shorter overall length. This was achieved through placing the bolt behind the trigger. Thus, Thorneycroft had created the world's first "bullpup" rifle, but the British Army was not impressed. Trials noted that Thorneycroft's carbine exhibited excessive recoil and awkward handling, leading to its rejection in favour of the Short Magazine Lee-Enfield (SMLE) rifle. Thorneycroft does not have any other firearms designs in his name.
This section also seems a good place to mention Albert B. Pratt's "helmet-gun". Pratt of Lyndon, Vermont patented a bizarre firearm in the guise of a soldier's helmet. The idea was that the user would wear it on their head as they would with a normal helmet, and the weapon was fired by blowing into a small mouthpiece attached to the firing mechanism via a tube. The protruding barrel of the gun had an aiming reticule attached to it that was in line with the wearer's eyes. The helmet could also be hollowed out and used as a cooking utensil, if necessary. It was made around 1916. The weapon, no absolutely nobody's surprise, didn't catch on.
===The Great War===
With the world at war from 1916 - 1918, firearms designers around the world were determined to produce new and better designs.
===The modern era: the 21st century===