Reply to Critics
One of the problems in replying to shooters is that they don't write much down on paper. Thus when you try to argue with them you get into constant arguments about what was and wasn't said. Fortunately the Combined Hunters and Shooters of South Australia (CHASSA) recently made a submission to the South Australian Animal Welfare Advisory Committee (AWAC). In what follows I'll refer to their paper as "the critique".
The critique claims correctly that my work was inspired by X-Ray studies showing many birds with lead pellets embedded in their bodies as a result of being shot. The critique then goes on to say "Naturally ingested shot shows up on the fluoroscope and there is no way to tell how many of these birds were counted as having been shot". This isn't true. Ingested shot shows up in the gizzard and is easy to pick from embedded shot. Researchers as far back as 1947 (see Whitlock and Miller had no trouble distinguishing between embedded and ingested shot. Norman in the largest Australian study, clearly distinguishes between pellets embedded in tissues and ingested shot in gizzards and clearly states that his "main table" relates to pellets embedded in tissues.
The critique goes on to say: "Also used as an inspiration for the program were tests done by Winchester in the 50's in which ducks were shot at given ranges and at one specific [emphasis in original] angle" . There are 2 errors in this little sentence. Firstly, Winchester's work (see Cochrane ) was done in the 1970's. Secondly, they only shot at ducks in profile because work done by other researchers in the late 60's indicated that this seemed like the best angle for killing ducks. For example, Andrews and Longcore shot 300 ducks head-on but the kill rates were far lower than for ducks shot in profile. At 40 yards with full choke using #4 lead, only 46% of ducks shot head-on were dead within 2 minutes; compared with 66% for profile shooting.
The critique relates that 93% of ducks were bagged at 40 yards in the Winchester studies. I should point out that Winchester used guns with very high choke (a very dense pellet pattern) and the ducks were always in the centre of the pattern. Out in the field both of these conditions frequently don't hold.
Next in the critique is a list of supposedly invalid assumptions used by me in building my model.
Much is made of the fact that a shotgun pellet cluster is 3 dimensional. It is a long "string" of pellets. CHASSA reckons the cloud can be 20 meters long. Roger Giblin of University College London (Dr Giblin runs a sophisticated shot testing facility for the University College London, it has a contract to test non toxic shot for the British Government and does various contract work for shot shell makers) gives a cloud length as 2.5 meters at a range of 35m. This is for the 80% of the pellet cloud which typically passes a target point (say at 40 yards) within 10 milliseconds, and the other 20% is strung out behind. I don't know where the CHASSA figure of 20 meters comes from --- probably shooter folklore. In fact, shotgun makers spend a great deal of time and money trying to find ways of reducing the length of the shot string and Giblin has tested shotshells where the full 100% of the shot cloud is only about 2.5m long. Why shotgun makers want to reduce shot string lengths is a bit of a mystery if, as CHASSA seems to imply, a long shot string is a better killer. I have a great deal of scientific respect for shotshell makers, they know their stuff.
The patterns I use are ideal in that they have a very short string length (zero) and correspond to what shotshell makers would like to make. By assuming short shot strings I will, clearly, underestimate wounding. Had I been able to model 20m shot strings mathematically the effect would have been to increase the wounding rates predicted by the model.
The critique continues in the same vein with criticism of my patterns. "[Russell] assumes, incorrectly, that the distribution of [the] pellets within the circle is random. This is not the case." What I assume is that the pellet distribution is bivariate normal, I have a letter from Winchester confirming this, I have email from Dr Roger Giblin confirming this, and it is also confirmed by published Winchester work in the 70's. So, what I presume about pellet distributions is very much the case.
Still on my patterns, the critique references Oberfell and Thompson and their measures of pellet pattern quality. Oberfell and Thompson (according to Williams ) judge the quality of a pattern by the number of "holes" (usually called voids) in it. The number of voids in a pattern is defined as the number of 125mm diameter circles which can be placed, without overlapping, inside the 76cm pattern reference circle without "covering" a pellet. I've tested a sample of my patterns and they are generally on the low side of the scale. i.e, they have a void count at the bottom end of the Oberfell Thompson range for the pattern density. My patterns are more even than those of a real shotgun .
Below is a sample. According to Williams this pattern (if its to be judged OK should have between 8 and 11 voids (the red "holes" in the pattern). The little crosses represent the pellets, and the other lines were used by the program which found the holes. As you can see, the number of holes of the proscribed size is at the low end of the specified range. I've tested many patterns this way and they are fine - according to the criteria. So, as usual, the shooters are just plain wrong.
Actually writing the program to find the red holes in the above pattern is mathematically very difficult, much more so than modelling shotgun shooting! My program misses some occasionally.
Next we come to a tedious claim. "Russell is using a cartridge containing only 141 pellets" . Not true. I present in SWC a model with equations which can be used for any number of pellets, also the computer simulation program can allow the setting of the number of pellets. The equations in SWC all use P, a variable. I used 141 pellets in the graphs in SWC as a concrete example of the results of applying the model in a concrete situation.
The next argument in the CHASSA relates to a paper by Tom Roster which I don't have. Taken at face value it indicates that some duck shooters are very much better than average. For this argument to be effective it needs to be quantified. How many duck shooters average at most 2 shots per bagged bird? Such shooters will have wounding rates somewhere around the 20 wounded per 100 bagged and some people may consider this acceptable. My only comment is that all the studies I've seen don't indicate very many shooters in this category. As already stated, Sanderson and Bellrose list a number of such studies --- including one by Roster --- and the super shooters seem to be AWOL. There is also an interesting and relevant study by Nieman et.al . This study was done in 3 regions of Canada and dealt with cripple rates (birds downed but not retrieved).
Cripples were first estimated by questioning shooters --- this is a common approach to cripple estimation in Australia also. But, in addition, researchers also watched those same shooters (According to Norton and Thomas , this is the only study of this kind --- where the accuracy of shooter cripple estimates was tested carefully.) from concealed hides and made their own cripple counts. The observers (Canadian Wildlife Service staff) counted between 5 and 8 cripples for every 10 birds bagged, but shooters admitted to around 2 cripples for every 10 birds bagged. Either shooters have appalling memories or they lie.
Note also that my wounding rates include birds hit but not downed so will always be greater than or equal to cripple rates.