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Shot balling – how it can affect your shooting performance and how to prevent it

Richard Atkins explores shot balling, which has had a long history but is more relevant today than ever

Man shooting shotgun in field

Shot balling has become a particularly pressing concern in recent years

Although most shotgun shooters will have heard the term ‘shot balling’, some may not fully appreciate what it is, what can cause it and, more importantly, how to recognise and prevent it. With balled shot able to degrade shot patterns – hence performance – and in addition be a potential hazard, it is somewhat surprising it seems so little understood or discussed.

 What is shot balling?

Shot balling is the result of combustion gases entering the lead shot load (usually with a felt or fibre wad cartridge), having escaped past the wad. The heat generated is intense and can melt pellets causing them to fuse together into clumps.

My experience of this – easy to see on a steel pattern plate – is for several clumps of fused lead pellets scattered among the pattern (and sometimes outside the main pattern). The similarity to a moonscape surface to some of my pattern plates is lasting testimony to how many balls have dented these steel plates while pattern-testing cartridges and new guns.

shot ball

A shot ball split this steel pattern plate

holed plate

The holed plate viewed from the reverse angle

Note that shot balling is not the whole shot load coming out as one fused ball. Although possible this would be potentially horrendous and, very fortunately, is not the most common manner that balled shot presents itself. There may well be some larger balls with other smaller clumps. These are obvious from the dark splat marks they make on striking the steel plate.

I have had balled shot split and pass through my steel plate from 40 yards while testing guns and cartridges. These are the extremes but do show the energy larger shot balls have. Their energy represents that of a dozen or more pellets in the ball and so has the ability to travel much further than any single pellets of the shot size fused together. This clearly has serious implications for safe shot fallout distances, whether on a clay shoot or in the field.

Check your gun and cartridge of choice on a pattern plate – five or six shots should suffice

Signs of shot balling

Signs of shot balling include where three of four pellets form a small clump

This shows a typical larger ball from a fibre wad and long cone gun

There are tell-tale signs balling is happening: a distant clay smashed as though it was a Skeet target shot with super-full choke is one example. Picking up a pheasant or pigeon with severe damage, such as a hole completely through the bird, or a head blown off, are clear signs of a balled shot strike. Only by testing your fibre wad cartridges through your gun on a pattern plate will you know for certain if balled shot is happening. I have heard folk say they know their gun or cartridges do not ball shot because they score well, in the field or at a clay ground. As the photographs with this article will show there can remain plenty of pellets in the pattern to bring about a kill, clay or game, even when shot balls are also present. So, please note that being happy with your hit rate does not prove your patterns contain no shot balls.

Note too that shot balling does not necessarily happen with every shot in a gun and cartridge combination that is able to produce it. There are often marginal circumstances whereby there are precursor indications that incipient shot balling could arise, but serious balling may arise in a percentage of shots. I have noted these signs where three or four pellets form a small clump on the plate, sometimes with tails or strings of three or more pellets in a line or curve, before a much larger shot ball dents the steel plate. These small clumps and strings are signs to look out for and indicate that it is worth conducting more tests to see if more serious balling occurs.

All the dents on my plates, examples of which are in the accompanying photos, occurred within less than 10 patterns. Given the potential risk involved with shot travelling much further than expected – such as when decoying with buildings seemingly a safe way off, or when game shooting when you can be shooting towards a beating line that is well beyond normal shot travel – it is very important in the field to take the time and effort to ensure your gun/cartridge combination does not produce balled lead shot. This is obviously in everyone’s best interest.

Miroku 800s

A battle-scarred Miroku 800s from the 1970s


The first step to preventing shot balling, so far as is practically possible, is to check your gun and cartridges of choice on a pattern plate. Five or six shots should suffice but, if the tell-tale signs mentioned arise then carry on to at least 10 patterns. Fibre wads are not all the same and can vary between batches. I have had cartridges that performed well but, when testing another batch, produced shot balls. Cutting some up to examine them revealed a proportion with less than round fibre wads and, in one instance, with a longitudinal groove on the sealing surface. Both of these flaws can allow the dreaded hot gases to escape, resulting in balling.

fibre wad cartridges

Fibre wad cartridges now often outsell their plastic counterparts

The use of a plastic obturator (sealing disc) under the fibre wad, replacing the over powder card, is a good method to help avert gas blow-by. These have been frowned upon in the past, but with the new bioplastics we are seeing being developed, there could well be merit in their wider use. I believe Gamebore now produce just such a bioplastic obturator.


Bioammo may be the way forward for avoiding shot balling in the future

I suggested just such a product to a very large component manufacturer some years ago, when reviewing the first water-soluble wad cartridges sold in UK and made by Armusa of Spain. Sadly there was no demand at that time so nothing happened, but I expect it to come soon.

Those with older guns built to the original principles for traditional wads are least likely to encounter shot balling but, given that wad quality can affect this, then a test with a new batch of fibre wad cartridges is still advisable. My testing over the past 10 plus years has indicated that any gun with extended forcing cones is potentially capable of shot balling. Many makers have gone this route and so it’s not possible to pick out makes.

Neither does it correlate that the longest cones are more likely to ball more those half as long. The greatest gas pressure, hence potential heat generation, is in the first few inches of the bore, and I have had severe balling from forcing cones barely 75mm long. Some such 12-bore cones are close to 10-bore in diameter in this area and fibre wads – which must be of a safe maximum size for use in bores of as small as 0.719in diameter – have difficulty sealing a bore of 0.040in-plus above the maximum 12-bore size.

An excellent way to ensure such modern guns suffer no balling issues is to use cartridges that use a biopolymer soluble or compostable plastic, or paper cup wad. These are now available from several brands, loaded with lead shot, including Bioammo, Eley, Jocker and Vouzelaud (as seen at the Game Fair) with others likely to follow.

More prevalent today

Shot balling has become more prevalent today, and to understand why it is necessary to follow shotgun developments over that period between Pauly patenting his breechloading gun to the present time. Breechloading shotguns require a well-formed chamber and smooth route for the cartridge contents to transition from inside the case to the shotgun’s bore. This transition is critical and central to where we are today.

Many noted gunmakers spent considerable time and effort to arrive at the best internal bore profile for efficient transfer of the shot load and its driving wads into the shotgun’s bore. This was during the golden era of shotgun development, which – from around the early 1800s to the early 1900s – saw the design refinement and sophistication that resulted in best English game guns. Such guns remain the pinnacle of perfection in form and function and height of desirability for those able to afford them. Competition to produce the sweetest shooting guns with the best patterns was fierce. Field trials were held with reputations at stake, as proven success ensured important sales.

This time saw the development of choke along the way. Choke was itself a considerable advance over the true cylinder guns that were most common before Greener’s work made choke something more widely understood and available.  (Read more on shotgun choke here.)

Critical cones

The key to the topic at hand is that section of tapered bore between the end of the chamber and the actual bore, known as the forcing cone. Forcing cones are, of necessity, tapered because they reduce the larger chamber diameter down to bore size.

Chambers must be large enough to accommodate the loaded cartridge case, which, in 12-bore, is typically 0.813in (20.65mm) at the chamber end where the transition point begins: the nominal bore size for 12-bore shotguns is 0.729in (18.5mm). Although this is the nominal size and adopted by many makers, the CIP-specified bore size for 12-bore shotguns spans a range of four size bands. These bands include all bores from a minimum of 18.2mm (0.7165in) up to a maximum of 18.9mm (0.744in) – a maximum difference of 0.7mm (0.0275in). This size range is significant.

Also important is that during all those years when shotguns and cartridges were being refined for optimum performance, all cartridges were loaded with what is now termed conventional or traditional wadding. Plastics wads were a long way off. Cartridges used then were therefore mostly hand-loaded – with wads cut from white wool felt – by the gunmaker concerned, and to strictly laid-down specifications for the equity of competition. Commercial-scale cartridge manufacture, as we know it today, was in its infancy. Other materials than felt were sometimes used for wadding, such as cork, paper, leather or card, with vegetable fibre coming along later. But white wool felt – with its good flexibility and ability to expand outwardly when compressed – was noted as the best performing wad material at that time.


Trials were conducted under the glare of critical and knowledgeable observers. These observers included the most keen and noted game shots (such as Colonel Hawker) as well as technical editors from sporting journals of the day including Shooting Times and The Field among others who, at times, also sponsored some trials. The most successful gunmakers wanted their stories and results told to an enthusiastic readership and, of course, advertising was all the more effective when one’s success was also noted in editorial matter.

So it was that gunmakers arrived at bore sizes, chambers and forcing cone profiles that produced the best patterns and penetration from their guns using cartridges loaded with traditional wadding. The most common configuration was for tight bores with 0.719in proof-marked bores common and with short forcing cones that typically were between ½in to 1in in length. Forcing cones were short enough to ensure that the wad was sufficiently into the bore proper to provide a gas seal before the rear of the wad left the cartridge case/chamber. And thus things mostly were until the advent of plastic wad cartridges.

There is a certain irony that the introduction of full plastic cup wads, which virtually eliminated the risk of shot balling, would play a key part in producing the conditions where it would return.

plastic wad litter

Landowners have become reluctant to allow plastic wad litter to lay on their land

The rise and fall of plastic wads

Plastic wads meant the efficient transition from cartridge case mouth to barrel bore became easier to achieve, because the sealing skirt at the wad’s base can expand much more than any fibre or felt wad. Also, with the lead pellets safely protected within a plastic cup, shot balling was virtually eliminated: much less hot gas escaped past the wads, and any that did could not enter the lead shot load to disrupt patterns. It was this ability to provide a good gas seal in larger than standard bores that lead some gunsmiths, notably in America, to claim performance benefits for larger bore sizes.

This was based upon back-boring existing gun bores, usually accompanied by extending the length of the forcing cones. From this grew a gradual trend among some gunmakers to sell new guns with larger bores, which some described as over-bored and others back-bored. These also featured longer forcing cones than were once common, with similar claims for improved performance. To what extent such claims can be verified by long-term results is for another time: it may take a while, because although the claims have been made for many years, even now there is still little qualified and quantified information available to be found.

It has been fascinating to observe, first hand, what has been happening since plastic wads changed the rules and gunmakers changed their guns to suit them. Leading gunmakers spent over 100 years coming up with bore sizes, profiles and forcing cones that brought the best out of shotguns during that time when only traditional wads were available. Then, after all that our forebears – some of whom were both excellent shots and technically proficient in gunmaking – had discovered, these principles were cast aside. Presumably it was thought plastic wads would dominate henceforth. That may have looked likely at one point but, since the BBC’s programmes about “drowning in plastic” were broadcast, the move against oil based plastics has gathered momentum. Landowners have become ever-more reluctant to allow plastic wad litter to lay on their land and this, as we now know, lead to the resurgence of interest in eco-friendly traditional wad cartridges. Fibre wads, being much cheaper than white wool felt, rapidly became very popular, and now often outsell their plastic wad counterparts.

Larger bores with much longer forcing cones are now common features for new shotguns, particularly clay shooting over-and-under guns. Just to compound matters, chamber lengths have almost universally increased to 76mm (3in) length, even though the most popular clay and game cartridges are loaded into 70mm (2¾in) cases. Using shorter cartridges than the chamber length of the gun they are used in brings another opportunity for reduced performance and gas sealing ability when using fibre wad cartridges.