|30" Circle Impacts
The SmallBoreShotguns team used a 30″ circle to count the patterns for the RWS cartridge since, un-fired, it contains more than 120 pellets. However, it is noticeable from all patterns available at the time of writing, that the pellets are concentrated into the center of the circle and therefore pattern slightly more tightly than the figures “on paper” suggest.
Whilst tightening of patterns is generally the opposite of what one would expect from very small shot (which will always be proportionately more damaged as it “scrubs” down the barrel), the low muzzle velocity (quoted: 600fps) clearly reduces this effect and will decrease pattern spread. The latter is probably the significant factor in this case.
Furthermore, it is rare that any of us shoot a gun which has a true cylinder choke – i.e. no constriction at all. (Many modern “cylinder” chokes actually have small, but measurable constrictions.) Where the muzzle diameter is identical to the bore size, there can be no deflection of pellets on the angled walls of the choke and no crushing together of pellets with associated deformation and damage. Although we expect a cylinder choke to pattern more loosely than any amount of constriction, this may not always be true, given that one significant source of pellet damage is completely eliminated. In the smaller bores, this effect is probably more pronounced and likely contributes to the overall tightness of the patterns thrown by the RWS cartridge.
With a larger stock of cartridges available, we could have shot more patterns, but beyond corroborating the observations made above, there may be little point. The RWS shell remains a somewhat unbalanced cartridge, with far too little individual pellet energy retained at long range (i.e. for a garden gun = 15-20 yards) to humanely dispatch even the smallest of game. In spite of throwing an excellent pattern, it is unlikely to be effective beyond 10 yards. At that distance, effective pattern area will be even smaller, probably requiring the gun to be aimed. In turn, this suggests the use of a larger, more effective shot size than #10.