I was recently at the range shooting a number of my rifles, but primarily my .257 STW, one of my favorite guns built on a Remington action with a 26 inch barrel plus a Vais brake. I was shooting a load that drives an 85 grain bullet at about 3900 ft/sec, and is very accurate. The weather was sunny, temperature about 75 degrees, no wind, about 50 ft above sea level. I shot a couple of groups at 100 yds, and all was normal. I switched to two hundred yards, and that is when things got weird. When the bullet passed through at about the 125 yd mark a perfectly round ball about the size of a basketball made of what I assume was water vapor appeared for just an instant and then disappeared. It was visible long enough to get a good look at it. It happened on every shot, and always at the same distance. It gathered a crowd and I ended up going through a whole box of ammunition because everyone wanted to see it several times. I tried a couple other rifles with slower bullets and could not duplicate whatever that was. We have all seen water vapor come off the wings of jet fighters at high speed turns, and these two phenomenon I assume are caused by the same thing. Has anyone else experienced this, and/or does anyone have an explanation of how this occurs? It has never happened again with the same gun and load, thank goodness. I should have charged admission.