So I'm sitting here with targets from my last three range sessions. Three weeks ago I was testing Vhit550 in my .300 WSM
Savage, behind 150Gr Combined Technologies BST's, going 63.5 to 65.5gr in 0.5gr increments. Have five nice groups with 64.0 and 65.5gr best, well under MOA.
Thinking faster is better, I loaded up some more rounds with 65.5gr and went back last week to try them out. Shooting five shot groups, the first one was right on the aim point, the second put three in a group 2" high, and the last two 1" higher. The third group started with the first round 3" high, the second 4" and the third 5", at which point I stopped and headed home to the work bench. Figuring something was loose, I re-tightened the stock bolts, the scope mounts, and the rings, adding medium loc-tite.
So today with my nice tightened up rifle it went like this.
Shot 1 for a starting point. Same point of aim, # 2 was 1" higher. #3 & #4 0.5" up from #2. #5 higher by 0.5". #6 thru 8 in a group 0.5" higher. #9 0.5" up. #10 & 11 grouped 0.5" up. #12 & 13 grouped 1" up. #14 0.5" up. So I basically have 14 shots in a column 1.5" wide and 5" high. All aimed at the same point of aim.
All shooting for these three sessions was done from bags at 100yds with 2 minutes cooldown between shots. Weather and wind were about the same for all sessions. The scope is a Burris Fullfield II 3X9X40 with Burris Signature rings and bases. At no time did I feel any looseness in the scope mounting.
Is there any load or rifle reason possible for this stringing? Or could there possibly be something wrong with the scope internally? If I had another scope sitting around I'd swap out and see what happens, but I'm currently a one-rifle guy and don't have a spare. Suggestions?
The 65.5gr loads are the max in the latest Nosler book, are pretty stout, and show a bit of primer flattening (CCI large rifle magnum primers) but no other pressure signs.