I have already posted some of this but would appreciate it if some of you would take another look. I am having a difficult time diagnosing the cause of my fliers. They are typically low. This is with my 9# 300 Win Mag. The barrel is a custom chambered Lothar Walther and stock is Rimrock synthetic. Action is trued. For example when shooting prone with Harris bipod and sling I shot two 3 shot groups at 400 yards. 5 of those shots were in 2.5” and one of the shots was low such that 6 shot group size was 6”. On another outing I shot two 3 shot groups at 500 yards. 5 of those were in 5.3” with only 3.5” vertical (one of those 5 was off to the right) but the 6th shot was quite low giving a 10” 6 shot group at 500 yards. I know that when those low shots were fired I most certainly was not aiming that low. So what is the cause? Assuming the bullets are not bad ones I can think of a couple possible items. I recently saw a video from the American Gunsmithing Institute that Darrell Holland did about long range shooting. Darrell Holland in his video said that the barrel should be freefloated to about 0.125” below the barrel and about 0.075” on the sides. My stock was originally set up for a barrel of smaller contour. I have tried to hog out the barrel channel more but started getting down to glass fibers so stopped. I have about 0.025”all around the barrel and more underneath it but I can still hear the stock hit the barrel when I rap on the stock with the palm of my hand. I wonder if when I am prone and tight in my sling if the barrel is hitting the stock sometimes upon firing. A friend measured the clearance when I was prone and tight in the sling and it was clearly less than when gun was at rest. Only other possible is that perhaps the position of the butt on my shoulder is varying somewhat. I do not think that is the answer as I am really trying to keep it consistent. Do you have any other possible thoughts? Many have said that a bipod on a hard surface can cause the rifle to bounce but Darrell Holland in the video is using a bipod frequently from a hard bench. Would a bouncing bipod cause a low or a high flier? Thanks for the help, Rufous.