In previous instalments we have looked at factors that affect shotgun performance and the role these various aspects, such as velocity and wad type, can play.
The critical role of the shot load has been highlighted and in particular the weight of shot charge, as this affects the sectional density (relationship between the height of the shot load relative to its diameter) of the loads. This becomes increasingly significant with the smaller gauges and emphasises the importance of using quality hard lead shot.
We have noted the typical shot loads associated with the various gauges and also seen how some of the latest ammunition moves away from those shot loads once deemed ‘ideal’.
Now we will look at the actual results on the pattern plate to see what effect this important relationship between bore size and shot load, not just what should happen in theory.
As previously stated, it’s all about achieving balance: it is important for us to know which factors are the most influential on performance and what actually happens. It is, after all, only actual pellets hitting clay targets that achieves the end result we are all looking for.
That is why patterning is so crucial, though it’s frequently overlooked or done in a perfunctory way. The test results obtained here will hopefully provide some insight regarding the importance of gaining a better understanding of what is actually going on.
We already know from the cartridge tests in Clay Shooting magazine that the patterning quality of the current crop of clay target ammunition in the typical 12-bore load (which we have concentrated upon until now) is at an all-time high. Performance has improved to make available to us levels of patterning ability, combined with speed, that were not available 20 years ago.
In part this has been driven by the official move to using lighter maximum shot loads in clay competition shooting. Cartridge makers must now bring together all the factors they know, and use new wads and harder shot, to make the best use of the reduced shot load in their cartridges.
The significant rise in lead prices in recent years also helped us recognise what is achievable with lighter loads, even in our ‘standard’ 12-bore guns.
Now we will see how the prime factors of shot load weight and shot size play out in practice. This should help all clay shooters, with whichever bore gun they choose to shoot with, make more informed choices with regard to ammunition.
The smaller bores provide an excellent insight as to what happens within any calibre cartridge. The increased breech pressures required to propel their higher-sectional density shot loads make any effects on quality more obvious.
Past testing has shown this to be the case, but things have moved on, so this month I chose the smallest practical end of the spectrum, the .410, and compared it with a competition load in 20-bore.
I selected the 14-gram and 19-gram loads from Eley Hawk, both offered in their latest Trap loading. Those wishing to test their prowess with .410s have a ready option of cartridges with clay-sized shot choices of UK 7.5 and 8, whereas the bulk of .410 ammunition is often only available with 7s, reducing the pellet count that can thicken up a pattern.
The 20-gauge chosen is the latest Eley CT Twenty competition cartridge, loaded with 28 grams of 7.5 shot. It too will have a higher sectional density than a standard 12-bore load of the same shot weight, but by a much smaller proportion than the 19-gram .410 load.
Something noted in past testing is that modern ammunition can require less constriction of the barrel to produce the pattern percentages that correspond with the established standard figures for defining patterns. Indeed, using chokes as tight as were once necessary can actually make patterns less dense. So that factor was included in the testing too.
Pattern testing requires us to know precisely how many pellets the cartridges being tested contain. Just working from charts of shot sizes and charge weights is not adequate, as too many factors can vary, such as actual shot charge weight and pellet size.
The 14-gram Eley Trap .410 loads were generous, with 14.8 grams shot load weight and 198 pellets. The 19-gram cartridges contained an average of almost 20 grams of shot (19.98 grams / 308.2 grains) and 271 of No. 7.5 shot.
Shot size gave pellet counts of 380 and 385 pellets an ounce – very slightly larger than UK 7.5 shot as defined by the tables. The shot in the 14-gram load was slightly harder than that in the 19-gram load, with crush values of 26.5 per cent and 30 per cent respectively.
The No. 8 shot 19-gram loads averaged 19 grams of shot (294.5 grains) with a shot count of 438 an ounce – again fractionally larger than UK No. 8 (450 an ounce). All these loads show precisely why this analysis is essential for pattern percentage result to be accurate and meaningful.
The CT Twenty loads were precise in shot load and pellet size, at 432.3 grains a load and pellet count of 389 an ounce (and 384 a load).
These results reveal that, in this gun, the heavier .410 Trap load did put more pellets in the pattern with the slightly lower choke boring (½ choke) than with full choke, recording 45 per cent to the full choke’s 32 per cent result and clearly indicating an ‘over-choke’ effect.
The difference is more dramatic than anticipated, leading to a retest just to confirm. Again this demonstrates the need for shooters to test their own guns and chokes with the ammunition they intend to use – do not assume a tighter choke will produce a tighter pattern.
The CT Twenty loads were tested in an Armsan 20-bore semi-auto with flush chokes. Even with a fibre wad load and this affordably priced gun, using just a half-choke, the results were excellent and compare favourably with similar 12-bore loads.
Despite the shot column being taller than a 28-gram load in 12-bore (therefore having greater sectional density), the selection of components gave the CT Twenty cartridges excellent patterns.
Next time we will look more closely into what these results mean when making ammunition choices, the performance potential of smaller gauge guns and some of the other factors involved, such as pellet deformation and shot string.