Written by Neil Harmse
Chapter 21. Shotgun Cartridges and Their Development Over the Years
Today most wing and clay target-shooters using modern shot cartridges show very little interest in the ammunition they use, apart from what they feel is their favourite brand and the ideal load for their specific sport.
To gain a better understanding of the development of centre-fire ammunition, we need to go back in time to the year 1850 and onwards, after the first breech-loading centre-fire guns became available.
Prior to then, from 1815-1835, gunsmiths were competing to get away from the flintlock. In 1830 the percussion cap, which was the intermediate stage on muzzle loaders, led to the development of pin-fire guns and subsequently opened the way for breech-loading centre-fire cartridges and guns. Thanks must go to Mr JV Needham, who invented and produced the ‘hammerless’ or internal hammer action that started the revolution in the development of the ‘modern’ style of ammunition. The centre-fire cartridge was designed.
In 1875, William Anson and John Deeley – who were both employed and associated with Westley Richards – developed and introduced the Anson and Deeley box-lock action, which was so successful in design that it has seen very little improvement up to the present day. This action was ideally adapted for the modern centre-fire cartridge. The action was less expensive and easier to produce than the traditional side-lock action, which was carried over from the days of the hammer and percussion actions. The Anson and Deeley action helped place guns in the hands of general shooters who were neither nobility nor landed gentry and could not afford expensive, handmade side-lock guns from top-name gunsmiths, but also wanted to get involved in the sport of ‘shooting flying’.
Side-locks were, and remain, more complicated to produce and are today sought after mostly for more expensive handmade top-grade guns.
The first breech-loading centre-fire ammunition was carried over from the days of muzzle loaders and used the traditional black powder propellant. When fired, these cartridges produced clouds of white smoke which sometimes obscured visibility for follow-up shots or even seeing the hits on targets. It was not unusual to see a shooter smartly dodge to one side to get past the cloud of white smoke in order to see the hit on his target. Soon there were calls for cleaner-burning propellant, which led to the development of Schultz powder. This burnt a lot more cleanly, producing less smoke and recoil, and was not as noisy as the old black powder loads. It became popular for its advantages to shooters. Further developments in modern smokeless Nitro powders led to more efficient and faster ignition, with more regular ballistics, less pressure and the absence of fouling, which also meant less corrosion in gun barrels.
Today cartridge manufacturers are continually striving to develop and improve the quality of their cartridges, with a view to more environmentally friendly components and consistent results. This is true of all the components which make up the modern cartridge.
The first step in the ignition process is the primer. Percussion ignition was first invented in 1807 by Rev Alexander Forsyth, a Scottish clergyman, but required a lot of refining. The early primers were very corrosive and could be unstable. Modern primers have vastly improved and have standardised on a 209-boxer type for shotguns which are largely non-corrosive, give quick and reliable ignition, and are well sealed and protected from contamination by moisture and oils, which are the cause of many misfires.
The following is a basic explanation of the firing procedure and sequence:
When struck by the firing pin of the gun, the primer should ignite, causing the propellant powder to burn and form a gas. This creates pressure, driving the wad and shot load up the barrel and, on exiting, causes the shot to spread into a pattern given by the choke selection, then on to the target.
Briefly, the modern shotgun cartridge consists of a brass or metal base, rimmed to fit onto the extractor or ejector rim of the action and chamber of the gun. The primer fits into this brass base. The body or case of the cartridge, which was traditionally made of varnished paper or card, is today usually plastic. The length of the cartridge body depends on the requirements of the gun chamber. This can range from 2½” (65mm) to 2,6” (67mm), 2¾” (70mm) and 3” (76mm). These are nominal lengths of factory cartridges, but exceptions are a shorter 2” (50mm) and a magnum 3½” (89mm), which are sometimes called for. The 67mm case was designed to allow the use of this cartridge length in either 65mm or 70mm chambers, allowing a slightly heavier load than normal for 65mm chambers.
Cut-away cartridge and wads.
Early cartridges all had fibre or compressed paper or card wads. Today the wad can consist of either formed or moulded plastic or biodegradable fibre. The plastic wad normally has a cup-shaped fore section with segmented ‘petals’ which hold the pellets in place and peel back and open as the shot column leaves the muzzle, releasing the shot in its forward motion to start spreading. This allows for a more controlled spread and pattern.
The fibre wad remains behind the shot load, acting as a gas seal and pushes it forward, with the shot column spreading faster on exiting the muzzle to create a more open pattern. The fibre wad is mainly used on game loads.
Most modern cartridges are enclosed with a segmented ‘star’ crimp at the mouth. Some cartridges can still be found with a ‘rolled’ crimp, but these are normally older or traditional loads.
As previously mentioned, with the trend towards environmental awareness, cartridge manufacturers have made great strides in the development and use of components that are ‘greener’ than in the past.
As a result of concerns about pollution of the environment (especially wetlands) caused by lead from shot pellets, cartridge manufacturers are now producing non-toxic shot using Bismuth, copper-coated or annealed steel pellets. These have a number of drawbacks, but research is ongoing. There is also a marked controversy in the claim that pollution from lead pellets causes problems. To date, no proof of this has been forthcoming, but it
is nevertheless wise to be proactive in this regard. For many years, lead shot had a 0,5% antimony added for hardness and this is now also treated by electroplating with either copper for hunting loads or nickel for clay target, small birds and pigeons. This reduces pellet deformation, keeping the pellets spherical to allow consistent patterns.
Pollution from wads has also been problematic, mainly in areas where high-volume shooting takes place. A number of game loads are now loaded with biodegradable fibre wads, which have a short lifespan once exposed to outdoor conditions. These wads are made from compressed wood materials, with paraffin wax as a binder to give added strength. Plastic wads are also a problem, especially in areas where they could be ingested by livestock. Research into the use of photodegradable wads, which have a limited lifespan when exposed to outdoor elements and sunlight, is ongoing. Plastic wads have a UV light stabiliser to give longevity, but photodegradable wads have this stabiliser removed or reduced, which allows them to break down into smaller pieces within a few weeks when exposed to sunlight.
Non-corrosive primers and progressive burning propellants are also the subject of continuing research in striving for more efficient and cleaner performance. Numerous overseas manufacturers, particularly in the UK, regularly select random cartridge samples from batches on their production lines and submit these for chronograph, pressure and velocity testing sometimes twice a day (morning and afternoon). Some have their own testing tunnels, but also send check samples to various proof houses. Some do tests of the loading machines for dosage rates of both powder and shot on an hourly basis. Velocity is measured at 2,5m and 10m from the muzzle and a ballistic analyser is used to calculate velocities. In this way, the quality of cartridges can be monitored and improved on an ongoing basis. Based on this research, UK and other manufacturers have a preference for single-base nitrocellulose powders in which the burn rate is determined by the surface area of the flake. For example, a larger flake area burns faster for light weight charges, whereas a smaller flake gives a slow burn used for heavier weight charges or smaller calibres where pressure build-up is rapid.
American propellants mainly use double-base nitrocellulose powder with an element of nitroglycerine added to it. This allows for a more energetic burn, but a dirty one, leaving residue in the barrel. An advantage of this propellant is that it is more stable in extreme temperatures.
The next time you load a couple of cartridges into the chambers of your favourite shotgun, spare a thought for the difficulties faced by early-day shooters and give thanks for the hard work, research and innovation that make our shooting today easier, safer and trouble-free.