URL=https://s1120.photobucket.com/user/Kawiekx250R/media/Lapua%20Polar%20Biathlon.jpg.htmTo illustrate the effects of wind and the importance of flags consider this image . Lapua Polar Biathlon ammo shot this morning . Had a pretty good ragged hole going , until …. , I missed a 180 degree wind direction change just as I touched the trigger . On the last shot no less . This wind direction change was not detectable at the firing position . Ahh , the joys of rimfire
Wind change may well have switched 180 degrees just as you touched the trigger. Such a sudden and rapid complete reversal of wind direction, as uncommon as they are, may be a possible reason for a notable change in POI. Perhaps there was a vertical component to the wind change as well.
Readers should note, however, that another very common reason for a change in POI is the nature of the ammo itself in the form of a flier. The ammo used in this case is an SK variety, be it Biathlon Sport, SK Rifle Match, or SK Standard Plus, all of which can have fliers. Even better ammo can have them. As Steve Boelter, author of Rifleman's Guide to Rimfire Ammunition and who has shot a lot of different ammos and rifles over the years in testing and competition noted, he would "see at least a few fliers per 50-round box of ammunition regardless of cost or manufacturer." He said that benchrest shooters claim that "high quality match grade ammunition should contain no more than a single flier per 150 rounds." Put simply, fliers occur because they are a fact of life in shooting .22LR.
One cause of fliers is differences in amount of propellant between rounds or differences in priming compound application and distribution in the casing. These are often detected not only on the target but also by the sound of the ammo when fired. At the same time fliers do not always reveal themselves with a audible difference in sound. Fliers or shots that do not have the same POI can be caused by other inconsistencies in the ammo. These inconsistencies include variation in base-to-ogive length, rim thickness, concentricity or run-out, differences in amount of lube on the bullet (a problem not unknown with SK ammo, which uses a greasy lube that can have unequal distribution between individual rounds), differences in bullet diameter or weight, or a combination of some or all of them.
Another cause of fliers is the rifle itself, or more specifically the bore or the chamber/leade. Sometimes irregularities or imperfections here may cause the occasional flier. It must be noted, however, that the small sample size -- "3 groups shot with 3 different ammo
Finally, while there's no reason to believe it necessarily happened here, fliers can be caused by human error. Even very experienced shooters will admit being responsible for errant shots from time to time, as does Steve Boelter in the book referred to above.
In the end, perhaps there wasn't a flier and perhaps the errant shot was caused by a 180 degree change that occurred with a rapidity that was impossible to detect until it was too late. But fliers do happen and they happen with a regularity shooters need to understand. They can be caused by the ammo, the rifle, or the shooter or some combination of these. Wind changes don't make shooting rimfire any more straightforward.
Edit: When I made this post I mistakenly thought the ammo shot with the target above was an SK variety but I see it's Polar Biathlon. My comments still stand.
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