Thoughts on shotgun ballistics
Jacques Botha
Forcing cones, tight patterns, interchangeable chokes and shorter pellet strings... What do these have in common?
Agunsmith once told me that shotguns were little more than imprecise pipes down which lead pellets are projected and ought never to be patterned (as this will destroy any confidence you may have had concerning them). He then concluded that the use of expensive ammunition in shotguns was largely an exercise in futility.
The reality is that modern high-grade shotguns are anything but imprecise instruments and that recent technological advances in shotguns and shotgun ammunition have been significant. In this regard, one has only to consider the following: Thirty years ago the combination of full choke and high- velocity cartridges would deliver 70% pattern concentrations (in a 30-inch circle at 40 yards) with a muzzle velocity of around 1 150fps. Now compare that with current competition shotguns that are capable of producing 95% pattern concentrations with full choke and
premium-grade ammunition at previously unheard of muzzle velocities approaching and even exceeding 1 400fps.
Furthermore, the seemingly endless fashionable quest for high pheasant shooting in the UK has demonstrated that the proper matching of modern shotgun barrel technology, tight chokes, premium ammunition and good marksmanship can produce consistent kills on driven pheasants at astounding vertical distances of up to 60 yards, as opposed to the previously accepted maximum of 40 yards. This amounts to a 50% increase in effective range.
Accordingly, recent advances in shotguns and ammunition have significantly improved both pattern concentrations and velocities, however these improvements are almost entirely applicable only to 12-gauge shotguns and ammunition. We have come a long way since the late 1970s when the American authority on this subject, Bob Brister, in his classic work Shotgunning: The Art and Science, demonstrated shot string and pellet deformation principles by patterning shotguns on elongated paper targets towed on a trailer behind his station wagon driven at set speeds by his (brave) wife.
PELLET INTEGRITY
Optimum shotgun performance is directly related to maintaining pellet integrity. On discharge, shotgun pellets are subject to significant forces as a result of acceleration, compression against one another, entry into the forcing cones, the barrel walls themselves and lastly the choke section of the barrel. Since deformed pellets do not fly straight, even slight pellet deformation has an adverse effect on shotgun patterns. The key to achieving optimum patterns is the preservation of pellet integrity by virtue of a combination of the following: 1. Uniformly round and optimally hard pellets resist deformation best, with all major shotshell manufacturers accepting the performance superiority of perfectly round hard pellets with an antimony content of 5%. This also explains why so-called “steel shot” is comparatively insensitive to pellet deformation and patterns significantly more tightly than lead shot, albeit with numerous other disadvantages. 2. In addition to going to great lengths to manufacture uniformly round and exceedingly hard pellets, premiumgrade shotgun ammunition manufacturers now plate these pellets with copper or chrome to improve hardness so as to further resist deformation, with the resulting pellets resembling perfect ball bearings. 3. Significant propellant advances, delivering specific, stable and even pressure curves, have also contributed to reducing pellet deformation and increasing velocities. 4. Shotgun wads have similarly undergone significant improvements to eliminate pellet deformation through both barrel contact and acceleration forces. In this regard leading competition ammunition wads now »
incorporate ingenious compression structures to resist acceleration shock and also match the pressure curves of the (highly specific) propellants employed. Hardly surprising, recent experimentation in the UK concerning bio-degradable fibre wad ammunition (where no barrel deformation protection is available to the shot column) has clearly demonstrated the performance inferiority of such ammunition in comparison to modern competition ammunition using protective polythene wads.
INFERIOR QUALITY
Since top-end shotgun ammunition manufacturers annually spend millions on research and development for their premium competition ammunition, the best components are invariably reserved for premium 12-gauge competition ammunition. This explains why such ammunition is decades ahead of that which are available in other gauges and why reloaded shotgun ammunition is incapable of matching premium-grade competition ammunition. Budget ammunition will contain cheaper and inferior components across the board and this is bound to show up on the pattern plate. As an example of this I once demonstrated to a wingshooter a 25% decrease in pattern concentration in his fixed-choke double shotgun by merely swapping to inferior-quality ammunition using the same load and pellet size.
CLAY TARGETS
Although clay target shooting is denounced by some as having limited relevance to wingshooting, I am of the view that valuable lessons can be learned from this sport. Consider this, the standard clay target, in its various target presentations, represents a reasonable approximation of the vital area of a similarly presented common gamebird, with both targets requiring three to four pellet strikes in order to produce a convincing “kill”.
GUN DESIGN
The remaining ballistic factors affecting shotgun patterning relate to the design of the gun itself. In this regard one merely has to examine the features of premium clay target competition guns to appreciate where your money has gone and why performance has so significantly improved: In order to eliminate pellet damage, the forcing cones of competition guns are very subtle and significantly elongated (often several inches long) so as to facilitate the gradual trouble-free entry of pellets into the bore. Serious competition shotguns exhibit a moderate degree of back-boring. Approximately 25 years ago my (new at the time) Beretta S687 shotgun featured absurdly tight bores of .719 inch (the industry standard is .729). Hardly surprisingly, this gun kicked like a mule and produced dismal patterns with all chokes save for the ½-choke tube, thereby rendering the multi-choke advantage null and void. By comparison, my current Italian competition guns all feature standard factory barrel diameters of .732 to .735 inch and produce excellent results. In order to gradually con- strict the shot column and limit pellet deformation, shotgun chokes have also significantly lengtened. Older fixed-choke guns and the first interchangeable-choke models featured very short chokes of only an inch in length. By comparison current interchangeable competition shotgun chokes are now between three and four inches in length. Military specification x-ray photography, now utilised by premium-grade ammunition manufacturers in their research, has greatly advanced the understanding of the dynamics pertaining to shotgun pellets in flight.
SHORTER, PERFECT PELLETS
Modern premium-grade shotgun ammunition, when matched with modern competition barrels, produce very short, compact and highly defined pellet strings of only 1½ metre in length at extended range. By comparison, obsolete guns and poor quality ammunition produce shot strings as long as 4 metres in length.
Premium-grade ammunition contains no deformed pellets and also produces very few deformed pellets when used in competition barrels, whereas budget-quality ammunition contains a certain percentage of already deformed pellets which invariably increase significantly on firing, all of which contribute to pattern deterioration, both insofar as pattern quality and concentration are concerned.
X-ray shot string photography has revealed that premiumgrade ammunition does not produce a distinct head, body and tail to the pellet string, as was previously the case. Accordingly, premium shotgun ammunition is more likely to produce multiple simultaneous strikes to a fast-crossing target as opposed to budget ammunition and older obsolete firearms where long shot strings result in only a portion thereof intersecting with the target.
BARREL LENGTH
As to the question of optimum shotgun barrel length, even with modern premium ammunition, barrel lengths beyond 28 inches produce minimal ballistic returns. No meaningful ballistic advantage is therefore gained by the barrel exceeding this length. Whilst specific applications may call for longer barrels, it is much more important that the shotgun itself is appropriately balanced and properly fitted to the individual shooter.
Individual preferences aside, 28-inch barrels are generally considered suitable for the average person; 30-inch barrels for persons of above average build and 32 inches for larger people. The advantages of longer barrels relate more to the gun matching the stature of the shooter, optimising balance and individual rib/sight picture preferences.
The case for premium-grade ammunition is put to rest by the fact that all accomplished clay target shooting competitors employ only premium-grade ammunition. My competition shooting experience led me to conclude that where challenging targets, such as those presented in Universal Trench clay target shooting (involving rapidly departing targets at initiation speeds of approximately 115km/h) are involved, pre- »
» mium-grade target ammunition will provide a substantial competitive edge of approximately five targets (in a round of 25) over budget-quality ammunition. The principle that there are no free rides in life applies equally to shotguns and shotgun ammunition.
CHOKE SELECTION
Where choke selection is concerned, it must be understood that choke is an expression of actual ammunition performance in that choke, with the choke reading itself being relatively meaningless. This is even more relevant with modern high-performance ammunition which generally produces far tighter patterns. To illustrate this phenomenon, the captain of today’s premium shotgun ammunition and modern com petition barrel technology is capable of approaching traditional full-choke performance (70% in a 30-inch circle at 40 yards) using as little as 3/8 choke constriction ( which would previously have patterned around 55%).
The best advice is still to utilise the least amount of choke that will consistently achieve the desired results. However, since gamebirds are almost never driven towards the shooter in this country and most frequently represent a wild, elusive and rapidly departing distant target with no vital areas directly exposed to the gun, sensible choke selection in most shoot- ing scenarios will normally involve a ½ choke (modified) or tighter.
The correct choice of gauge, load and shot size selection involves a delicate balancing act with respect to the following: 1. Although patterns are never absolutely perfect, pattern quality is always the primary consideration. 2. The Holy Grail of shotgun patterning – tight and perfectly even patterns in a 30-inch circle at 40 yards – is practically unobtainable. Since patterns are always more dense in the centre, American trap shooting expert, James Russell, recommends abandoning the assessment of the fringe pattern in a 30-inch circle and to rather evaluate only the inner 20-inch circle thereof. 3. There is a definite limit as to the quantity of pellets one can simultaneously force through a shotgun barrel of a specific diameter before pattern quality begins to deteriorate dramatically. This explains why heavy loads in the 20 gauge are incapable of matching the performance of similar loads in the 12 gauge. 4. While lighter loads give superior patterns and significantly increased velocities, pellet counts are naturally worse and there are limits to velocity increases before pellet deformation becomes a problem. The inefficiency of shotgun pellets results in sig- nificant velocity losses downrange, with the muzzle velocity being halved at 40 to 45 yards. While increased muzzle velocity is an advantage, it does not equate to the expected reduction in forward lead. My pattern evaluations have led me to conclude that premium-grade 24-gram Olympic competition shotgun ammunition produces excellent high velocities, patterns very well and exceedingly tightly, to such an extent that it is only marginally behind similar 28-gram ammunition. Further benefits of this ammunition are reduced recoil and marginally reduced forward lead as a result of the increased muzzle velocity. 5. By comparison, heavy magnum shotgun loads are notorious for low velocities, increased wear and tear on the gun, excessive recoil and poor pattern performance, all of which also come at greater expense. Once again, there are no free rides. 6. Other than the advantage of reduced gun weight and a lighter, fast-handling shotgun, smaller gauges produce inferior performance with ridiculously expensive ammunition which also lags decades behind 12-gauge performance ammunition. Do not bother sending in angry letters, because 20-gauge shotgun performance has been consistently and conclusively demonstrated as incapable of matching that of the12gauge. After all, if the 20 gauge was even half as good as its proponents would have you believe, why do all competition shooters of any standing, including women and teenagers, only use the 12 gauge? In other words, do not hold your breath waiting to see a 20 gauge on the podium at the Olympic Games. 7. While the larger shot sizes retain superior momentum and penetration at extended ranges, for reasons not fully understood, they pattern more openly than the smaller shot sizes with patterns lacking adequate pellet counts. Simply put, vast disturbing holes appear in patterns once you drop below no.4 shot. 8. While the smaller shot sizes generally produce superior patterns, the individual pellets run out of adequate momentum and therefore penetration at extended ranges.
In the pursuit of the ultimate high pheasant shotgun load, exhaustive testing in the UK has conclusively demonstrated the overall superiority of a premium-quality 12-gauge, 34-gram English no.5 shot cartridge. When matched with a shotgun with all of the discussed features of competition barrels and sound marksmanship, this combination produces consistent kills on driven gamebirds as high as 60 yards and even as far as 50 yards on departing targets, however the shooting of all geese must be limited to 45 yards to accommodate larger shot sizes (preferably no.3) which produce reduced pellet counts and significantly poorer patterns. In conclusion, other than the specific examples of geese, quail and pigeon shooting, the South African wingshooter can do no better than to select a premiumquality 12-gauge cartridge utilising English no.5 shot in either a 32-gram or 34-gram load and to pair this with a modern shotgun featuring competition barrel technology.