waterman,

  Good questions all, but I'm afraid I have no definitive answers to many of them. The wall in question was about 5 ft. from the bench I was shooting off and is about 10yds. long, and 7 ft. high. It's used to separate the 25 & 50 yd. shooting line from the 100 yd. range, so that both ranges don't have to be shut down when the pistol shooters want to look at their targets.

  The first time this happened I just put it up to a bad day at the range. Two days later it happened again. I don't know why I thought of it, but the idea that Franklin Mann had shown in his book that placing a plank under the muzzle and extending it outward caused a deflection of the bullet. His conclusion was that you had to have the muzzle of your rifle extend beyond the end of the bench or bad things were gonna happen.

  Normally I shoot from the 2nd bench out from the wall, but on this occassion GWArden was using that so I moved my stuff over to the 3rd bench and the groups returned to normal. When shooting off the 2nd bench groups are all normal. Now we're not talking about a 1/2" or so difference, we're talking groups getting blown out to 3 & 4" from a normal under an inch.

  Was this anomaly caused by the wall, or something else. I can't say for sure, but that's how I look at it. It might not be the wall itself causing the problem but the air moving around the outer end of it and coming back in, in a swirling motion. Prevailing winds are usually from the 9 o'clock side and the rifle benches are on the 3 o'clock side. As we know the first 25 yds. or so from the muzzle are the most critical in getting the bullet stabilized as it's motion moves from a center of form to the center of gravity. The inference could be then that this swirling action could be causing an unusual irregular amount of disturbance to the bullets flight.

  Of course the next question would be how come the other benches aren't affected. Another answer might be that the wind coming around the wall causes a slight vacuum to occur which is not particularly strong but enuf to affect a bullets filight near the wall but would disipate rather quickly as it moves out away from it.

  There's a coupla answers for you which might be the cause, or none of them are. Until some actual testing is done to try and figure it out that's the best I can give you. In the meantime I don't shoot on the bench next to the wall! 

  If either of the above is true then a .22 bullet would be affected more than a heavier one.

  As to any effect indoors..... I've never noticed any, but then most indoor ranges have fairly enclosed firing points so one point would give the same effect as any other. Also you don't have any cross air current of any consequence since most indoor ranges pull the air down range from the firing point.

PETE

Willis,
  You are right about the effects of Mann's experiment. It just happened to pop into my head as I was trying to figure out what could cause such a disparity in group size from one day to the next, and then the return to normal after moving.

  It might be that nothing caused the problem other than some bad shooting on my part for a while, and changing benches just got my mind going in the right direction. At this particular point in time I just don't have the time to see if the effect is repeatable, and whether it affects other guns in the same way. It would be interesting to do the experiment tho! 

  Ever since I read that experiment in Mann's book I have been careful to extend the muzzle of my rifles past the end of the bench. Maybe some day I'll see if I can repeat what Mann observed.

PETE

Joe,
  Part of the problem was that the rifle I was shooting..... the .28/30..... was a known quantity. What I was doing was just getting the sight settings for an upcoming match that Saturday. That's what was so confusing, and still is for that matter, since without further proof my suppositions are just guesses anyway.

  Except for a match most shots are over a chronograph. I like to, if possible, always build up a "bank" of data on a gun. MV's, ES's, SD's, and groups, so when something out of the ordinary shows up I can spot it right away and look for the cause. This also builds up the confidence level in that gun, so when I go to a match I KNOW the gun will shoot up to a certain level of performance and if it doesn't then I know it's me or some condition I'm not reading correctly...... Like a coupla targets this past Saturday.   

  On these two occassions the chronograph showed that things were normal. If it hadn't been inside the norm then I would have suspected something internal, like fouling build-up or Leading, which lead to the comments in my other two posts.

PETE