There are a host of other variables that may or may not affect the results that you obtain. For the sake of discussion, do you shoot three or five shoot groups over the chronograph. Will a new rifle require a different shooting technique to “break in” a new barrel; will such a process influence the final outcome?
My personal option is to shoot three shot groups, a statement that will no doubt cause headshaking by some who read this. Whenever this subject is raised those in favour of five shot groups mutter something about statistics and then move on. This raises another question.
Who decided that five shots groups should be the norm? Why not ten shot groups? Perhaps twenty! Could there be other reasons why five shot groups are larger than three shot groups? Could it possibly be that the speed of shooting causes extra barrel heating. Further, what about the increased amount of barrel fouling caused by the extra shots? In any particular rifle when exactly, do groups start to “open up” due to barrel fouling?
What I am suggesting is that five shot groups are nothing more than accepted opinion. Yes there are a lot of questions but if we are to achieve any meaningful results they do, I suggest, need to be investigated and answered.
The evidence of twenty five years of hand loading leads me to suggest that after ten shots, in some rifles, barrel fouling will cause a measurable increase of group size This increase would be of concern to a benchrest shooter, possibly to a long range shooter but not worry a hunter after bigger game. Is this the reason that bench rest shooters frequently clean their match grade, lapped barrels?
In addition the amount of fouling is, in my opinion, affected by the type of barrel steel. Is your cleaning process valid and consistent for a particular type of steel? It is possible that my current frequency of cleaning is, for testing purposes, incorrect. If we are really serious should we clean the barrel after each group to apply a further consistency to the testing process?
Is your barrel clean to start with? Are you sure that the group you shoot is reflecting the performance of the rifle and ammunition? Are you, the rifleman, sufficiently experienced to call each shot?
Is there in fact a solution that will allow for these variables so that the result obtained is meaningful? Do different powder and ammunition companies use the same standards to develop loads? Are there in fact any written standards?
Wind velocity is a constant problem that may be overcome by shooting either very early or very late in the day. If you do this it may cause chronograph problems. Temperature may also cause problems at a later time. If you have developed a load that does not exhibit pressure signs in winter there is no guarantee that it will be safe to use in the heat of summer.
Let us assume that you have a rifle with a clean barrel and a batch of suitable ammunition at a constant temperature. The morning is windless; you switch on the chronograph and begin to shoot. This raises the first question. Do you fire a single shot to “dirty up” the barrel before attempting to shoot a group? I believe that this is necessary as few rifles with a clean barrel will print a first shot in the same area as a dirty one. It may also be used to make sure that the chronograph is working correctly.
Do they always test under controlled conditions or are some of their tests outdoors? Can we, as handloaders, hope to duplicate the results that ammunition companies achieve?