Lead shot vs steel: The Field’s guide to the ballistics
Lead has been used for centuries to deliver a clean kill. What must a gun know before deciding on its replacement?
What must a gun know before deciding on a replacement for lead? Simon West analyses the options
WRITTEN BY SIMON WEST
The organisations that represent live-quarry shooting have said that they want to move away from the use of lead shot over the next five years. Quite an ambition, and something some gun and cartridge manufacturers have been working on for years. But is it attainable within the limits of science and today’s guns?
Hitting a bird with enough energy to produce a clean kill is the core skill of every shot. In the gameshooting world, lead has been the projectile of choice for centuries. It is dense, soft and cheap, and a perfect material to transfer energy from gun to target. But, as we now know, its chemistry has a harmful effect in living organisms. That evidence obliges us to look for alternatives to reduce the overall effect on our environment. So, what else is available to do the job?
To produce that clean kill, we need to fire enough shot with enough energy to provide coverage and penetration. That combination of pattern and lethal energy transfer is the collective responsibility of gunmaker, ammunition manufacturer and shot. Almost all our guns have been designed around lead shot as the primary projectile but that doesn’t mean we can’t use other materials, if we provide coverage and penetration.
So, what are the options? Physics reminds us that kinetic energy is reliant on velocity and mass.
Velocity depends on the gun and propellant accelerating the shot load along the barrel. For that we need pressure and that brings us to our first challenge. Modern guns, with modern steels, can be manufactured to work at very high pressures. The superior service pressure to which they are designed is 1050 bar (~15,000psi). Older guns are only designed for standard nitro pressures of 740 bar (~10,000 psi). There are also proof limits for some ammunition on velocity and momentum; but more of that later. Mass is dependent on density and size. The denser the material the better, and lead scores well. Looking for alternatives we want to get close to lead’s density or we need to increase the size of the shot. The bigger the shot, however, the quicker it loses its energy travelling through the air.
LEAD ALTERNATIVES
Right next to lead in the periodic table is bismuth. It has 85% the density of lead and is non-toxic. Cleverly alloyed with small amounts of other metals, it loses its inherent brittleness and becomes a worthy candidate as an alternative. The problem is that it is rarer than lead and therefore more expensive.
Tungsten, another non-toxic metal, has great density (170% over lead) but is expensive and very hard. It can be mixed as a powder with polymers to create shot with a similar density to lead. This has been effectively used as an alternative for many years, but prices are still high.
Which brings us to iron (or ‘steel’). In the world of cannon artillery, iron shot replaced lead hundreds of years ago. It has great strength, is freely available in nature and is non-toxic in living systems. Perfect? Well, there are some challenges. First is its density – only 70% that of lead. To achieve the right kinetic energy we need bigger shot. Bigger shot means fewer pellets per ounce and that affects our pattern density. Bigger shot also means it loses its energy quicker at range – where we need it to do its work. Secondly, although the shot used is made from ‘soft iron’ it is far harder than lead. In the gun we need to protect the barrel walls from the iron shot by using a cup wad. It also deforms less than lead shot so doesn’t ‘squeeze’ as well
through the chokes. That said, as the pellets stay spherical, they do fly better and pattern well with less choke constriction.
To ensure that chokes are not overchallenged, there are proof limits for steel shot cartridges on velocity and momentum. There are two types of steel ammunition: ‘standard’ and ‘high performance’. For standard steel cartridges that can be used in a nitro-proved gun, the velocity limit is 425m/s (1,395ft/s). This is similar to standard lead cartridges. High-performance steel cartridges must only be used in guns proved for steel and showing a fleur-de-lys proof mark.
We should see the gun and its ammunition as a system designed to work together to produce a specific effect. For the ballistics challenge we are considering there are six important parts: the chamber, the barrels, the choke, the propellant, the wad and the shot. Vary one and the others need to compensate to produce a similar effect. But some of these parts have limits on what can be changed. Many older sporting guns have only 2½in chambers. This presents a real limit on what we can fit in, especially as steel shot needs to be fired in a cup wad to protect the barrels. Chambers of at least 2¾in provide that extra room.
The choke, designed to concentrate the shot at range, can present a problem. To get a good, tight pattern with lead shot, many guns have tight chokes. We cannot fire steel shot through tight chokes. There is less compressibility with steel and firing a steel load at the neck of a tight choke will stretch the steel and produce a ‘ring bulge’. Whilst not necessarily causing a safety issue, a reshaped end
to your barrel will not look good, will take it out of proof and reduce its value. The Proof Houses advise not to fire steel cartridges at more than half choke.
Actually, that lack of compressibility gives us an advantage with steel. The spread of lead shot is partly created by the mis-shaped pellets flying less aerodynamically. The more spherical pellets of steel provide better patterns with less choke.
Gough Thomas, one of the leading shotgun ballistics experts of the 20th century, determined the terminal ballistics requirement for gameshooting. He stated that what was needed was:
• small birds, such as snipe: two pellets, striking energy at least 0.5ft lbs;
• medium birds, such as partridges and grouse: three pellets, striking energy at least 0.85ft lbs;
• pheasants and duck: four pellets, striking energy from 1ft lbs to 1½ft lbs; and that to achieve this a minimum shot pattern of 120 pellets in a 30in circle is needed.
The late Ed Lowry can be considered as one of the experts in the field of shotgun ballistic research. Working for Winchester in the ’70s and ’80s, he conducted extensive trials in steel and lead shot and developed the theoretical modelling for shot energy. Using his calculations, we can determine the theoretical energy of the two types of ammunition we have selected for a trial. The steel pellets start with more energy because they are bigger but lose their energy faster because they have less sectional density.
COMPARISON TRIALS
The COVID-19 pandemic has prevented us from conducting all the trials we need but as a first stab we did a basic comparison of lead and steel ammunition at 30 and 40 yards using ¼ and ½ chokes. Using the advised ‘two sizes larger’ we compared lead No 5 and steel No 3 shot in 2¾in standard cartridges (32gm of shot each). Although we would get more steel pellets of the same size to the ounce, going two sizes up means we get fewer steel pellets in the cartridge (155 steel vs 242 lead).
The two cartridges selected for a firing trial were both ‘standard’ steel loads that can be used in a normal, nitro-proved 12-bore with 2½in or 3in chambers. They were: steel - No 3 (3.25mm) 32gm, muzzle velocity 375m/s, 70mm case, degradable cup wad; lead - No 5 (2.8mm) 32gm, muzzle velocity 391m/s, 65mm case, degradable wad.
ENERGY RESULTS
Firing at standard 10% ballistic gel at a distance of 40 yards, we can examine penetration energy.
The seven lead pellets that hit the gel penetrated to an average of 9mm; the four steel pellets penetrated to an average of 9.3mm.
Unlike high-velocity bullets that produce shock damage as well as a wound channel, shotgun pellets must just hit vital organs to do their damage. This basic comparison would suggest the energy of the steel pellets compares well with lead – proof of the theoretical model.
PATTERN RESULTS
Using standard 30in pattern boards we were able to do a rough guide to shot pattern density. With fewer pellets in the load, the steel cartridge faces a challenge on filling the pattern but produced good results at 30 yards. At 40 yards, even though the percentage of pellets hitting the circle was comparable to lead, the density had fallen below the Gough Thomas requirement of 120.
This trial was based on a small number of shots and only two cartridge types. However, it shows the need for shooters to get the right balance of pellet numbers and pellet weight. In this example, there is scope for reducing the pellet size a little to maintain penetration and then get the desired density at 40 yards. The theoretical model shows that steel No 4 shot would still have 2.1ft lbs at 40 yards and, of course, fill the pattern better. In the end this can only be tested in your own gun with different cartridge types on the pattern board.
What is interesting is the close match between the steel results in the different chokes. The high percentages of pellets hitting the circle even with only ¼ choke would suggest that opening the chokes of old guns to reduce the risk of ring bulges is a nobrainer. Ultimately, what these trials show is the realistic killing power of steel cartridges; easily at 30 yards and, with the right ammunition match, at 40 yards.
Right now, we have the beginnings of effective steel cartridges for the 12-bore system but only in 70mm (2¾in) cases; 65/67mm (2½in) options should appear over the next year but with smaller loads. Twenty-bore solutions are starting to appear. Smaller bores, with the limited spacefor components, may well appear but their performance will need to be tested.
WHAT ARE YOUR STEEL OPTIONS?
First, look at your gun and read the proof marks. The important things to look for are: proof – must be nitro proved for standard steel, steel proved for high performance; chamber size – the cartridge must be a fit or smaller than the chamber; choke – half choke or less for steel.
Does it have damascus barrels? If so, steel shot is not currently recommended. Bismuth shot is your best alternative. It’s expensive but for those special days, with your old gun, probably worth it.
The chamber size is stamped under the breech. Depending on the age, it will give the size in inches or millimetres (mm). If it says 65mm or 2½in, you will not have steel cartridges available yet. Lead, tungsten or bismuth are your options for now. That said, many old guns have had their chambers enlarged to 70mm and re-proved. You will always have more choice in the future with a 70mm chamber and you should discuss this with a gunsmith as an option.
The proof mark is critical. To fire a standard steel cartridge, you need to see a nitro-proof mark from one of the British or CIP houses. If you are lucky enough to have a fleur-de-lys, you can explore the highperformance steel cartridges. The chart above has been produced by the British Proof Authority to help gun owners understand proof marks. It shows the marks in the two left-hand columns that would allow you to shoot standard steel cartridges; the righthand column shows the marks that allow you to fire high-performance steel as well.
Finally, measure your choke. For a 12-bore gun to be able to fire any steel ammunition you must have a maximum constriction of 0.5mm (0.020in); that is, half choke or less.
Only with all three meeting the requirements – proof, chamber size and choke – can you start on your steel testing. Take advice from a reputable dealer or gunsmith on what ammunition would suit your type of shooting, then get out with some pattern boards and give it a go. You can also discuss what changes your gun might accommodate.
Lengthening chambers, reducing chokes and submitting for re-proof might be beneficial.
Over the next few years, we will see further ammunition products become available. As they do, we will need to test their effectiveness. Optimising for steel shot is best built into guns at the design phase and I expect new guns to exploit technology and high-performance loads to deliver ever better performance. The old gun is not written off yet; we have great companies working on the solutions. They have led the way through the adoption of breechloading, nitro-propellants and biodegradable wads. I expect many happy years of taking the old gun out and enjoying effective shooting.
Simon West is the director of the Gun Trade Association, an MOD deer manager and a game shot. Previously in the Army, he led ballistic research for artillery guns. He has been making his own cannons for 23 years.
Optimising for steel shot is best built into guns at the design phase