Historically, the most common configuration for the muzzle-loading shotgun was either a single barrel or a side by side shotgun with side locks, The side lock, side by side shotguns remains the most common configuration for modern muzzleloading shotguns encountered today. However, historical examples of muzzleloading shotguns are not limited to the "traditional" side lock style. During the muzzle loading era, shotguns were produced in a wide array of configurations, including guns with side hammers and underhammers. Both the underhammer and side-hammer guns are not only historically correct, they can also provide some distinct advantages over the "traditional" side by side with side locks.
Historical Examples -- Underhammers
As the name implies, an "underhammer" lock is a lock where the hammer is below the barrel. With percussion guns, the nipple generally point direcly downward and percussion cap is held in place by friction. The underhammer principle was originally developed to improve flintlock ignition. The basic idea was that frizzen would hold priming powder in place until moved downward by contact with the flint. The shower of sparks caused by the flint's contact with the frizzen would ignite the priming powder in mid air -- directly below a downward facing flash hole. The resulting upward flash is just fractions of an inch from the flashhole and ignition is virtually instantaneous – at least in comparison to the traditional upward facing flintlock. The underhammer flint lock never gained wide spread acceptance. However, examples of underhammer flintlock guns can be be found a website known as the Underhammer Society.
Development of practical underhammer guns began in earnest following the invention of the percussion cap. The father of the American underhammer is generally considered to be Fordyce Ruggles. Fordyce and his brother, Adin, set up shop in Hardwick, Massachusetts in December of 1825 were they began producing underhammer guns.
The underhammer design had a number of advantages. First, underhammers where simple. Many underhammer designs have less than five moving parts. This stands in stark contrast with the traditional side lock which has many parts which must be precisely fitted in order to create a functioning lock.
In addition, the underhammer design has a very short flash channel. The nipples of the gun are generally threaded directly in to the barrel. The short flash channels make for more positive ignition and faster lock times. While underhammers did not displace the traditional side hammer guns, they did become poplar in certain regions of the United States, particularly New England.
Most underhammer guns were single barrel affairs. However, a number of examples of multi-barrel underhammer designs have survived. Pictured is above is a very interesting SxS underhammer shotgun and a hybrid O/U which uses one underhammer lock and side lock. In many cases, the multi-barrel guns are combination rile/shotguns. On the barrels is rifled and would be loaded with a single projectile, such as a patched round ball. The other barrel would be loaded with shot.
Historical Examples -- Side Hammers or Mule Ears
Another variation on muzzle loading lock is the side hammer which is also known as "side slappers", "Mule Ear" locks or simply "Muley's". As the name implies, the hammer of a side hammer gun hits the percussion cap from the side. Side hammer guns began to appear in the United States during the 1820's It is thought that the original side hammer guns where developed as a simple mechanism to covert a flintlock gun into a percussion gun. In such a conversion, the nipple would be screwed directly into the torch hole of the flintlock barrel.
The side hammer is a true American design! as there is no other records, from another country, that show this innovation. Like underhammers, side hammer locks also tend to be simple. Sider hammer locks can be created with a minimum of tools and a limited amount of precision machining. Side hammers also have a short flash channel. The nipples of the gun are generally threaded directly in to the barrel. The short flash channels make for more positive ignition and faster lock times.
The configuration of side hammer locks lend themselves to mounting two barrels in an Over/Under configuration. The accompanying pictures show two examples of period Over/Under guns with side hammer locks. In both cases, the guns are combination rifle/shotguns with one rifled barrel and a smooth bore barrel for use with shot.
Modern Examples of Underhammer and Side Hammer Shotguns
Underhammer and Side Hammer shotguns remain as popular designs among many modern muzzle loading gunsmiths. I believe that this is true for a number of reasons. First, as noted above, the Underhammer and Side Hammer locks tend to be simple. There are relatively few moving parts and construction of either type of lock can be accomplished with only basic tools. Second, Underhammer and Side Hammer guns tend to have short flash channels making for faster ignition. In addition, on both Underhammer and Side Hammer guns there are no hammers extending above the plan of the barrel. I my view, this is a particular advantage when shooting at clay targets. Whether or not you are aware of the hammer ears, I am convinced that having them in your field of view will have a distracting influence when swinging on a hard angling target.
Every once in a while you will see a side hammer gun from Tingle Mfg. Co of Shelbyville, Indiana. These guns were made in the 1950's and most of them were custom order, as there is much variation in types, sizes, and shapes.
Below are a selection of pictures of Underhammer and Side Hammer shotguns from various muzzleloading events. As you will see there is a wide variety of styles for these guns. Maybe this will inspire you to build your own.
Bill Cole O/U Side Hammer
Bill Cole built his own O/U Side Hammer gun which has some very interesting features. If you look closely, you will notice that Bill's gun has only a single trigger. Unlike most modern O/U's, Bill has set the trigger to fire the upper barrel first. This was done so the shooter would not be required to hold the hot, lower barrel after firing the first shot. As you will note, the wood fore-end does not completely cover the lower barrel.
Dustin Parker of Canyon City, Colorado has built an two 10 bore shotguns on the Hillard Underhammer design. Dustin shoots one of two guns pictured below and his brother shoots the second underhammer. Dustin's gun is cylinder bored and the other gun has a jug choke. Dustin usually only uses his 10 bore on the 10 yard trap field.
While Dustin's gun is an elegant piece of craftsmanship, he is probably best known as the guy who occasionally shoots with his parrot (Kelly) on his shoulder. If you run into Dustin and Kelly on the range do not try to pet Kelly. He bites!
Deak Flinchbaugh Underhammer
Deak Shoots an Underhammer shotgun which was based on an old Hopkins and Allen Underhammer with a modern shotgun barrel. As you will note, Deak's gun is complete with ventilated rib a poly choke.
Tom Hart Sidehammers
Tom Hart from Canyon City, Colorado has made a number of side hammer guns. Many of the competitors at the NMLRA shoots are using Tom's guns. At the 2011 Western National Shoot, Tom won the low-gun skeet event with one of his guns. Doc Bell won the double skeet event with one of Tom's guns and Rady Dyer won the skeet championship with a gun which has been converted to a muzzle loader by Tom.
My personal gun was made by Tom. If you are looking for a custom mule ear gun, you should definitely talk to Tom. All of Tom's guns have unique design which incorporates a receiver to house the locks. . Here are some pictures of one of Tom's guns.
Rod Gates Mule Ear
Rod Gates of Cross Timbers Missouri is a well known for is his fine large bore muzzleloaders. Rod is pictured in the upper left picture holding his 8 bore SxS which he uses on the Sporting Clays and Skeet ranges.
One of Rod's current projects is a 4 Bore (approximately1.052 inches in diameter) side hammer shotgun. The big four bore is still a work in progress, but Ron gave it a successful test run at the 2011 Shotgun Soiree. The gun weighs approximately 11 pounds and shoots a load of 5 1/2 drams of cannon powder and 1 5/8 ounces of shot.