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Left to Right impact change with bullet weight

gunprofit
Has anyone ever researched why you get left to right bullet impact when changing bullet weights. It was most notable recently while working up loads for my 7.5 Schmidt Rubin K31. I sighted in with 168 grain at 300 yards. Once in the center of the target, I changed to my 155 gr palma bullets. They struck the target almost 2 1/2" left of center. Then I changed to my 175 grainers and they struck the target over 2" to the right of center. This is approaching a 5" left to right bullet impact difference between 155gr & 175gr at 300 yards. I have seen this before with different loads, but never to this extreme. All the bullets used were Sierra Match Kings. The powder was Varget. Of course, velocities were different between bullet weights. The wind was calm throughout the shooting. The barrel twist for a K31 is 1 in 10.6", so I know the are stabilized. I have no complaints about accuracy with this rifle as it always shoots sub MOA. In fact, I can get 1/2" 3 shot groups on a regular basis with the 168 gr Berger VLD bullets. However, Berger bullets cost me $10.00 more per box of 100 over the Sierra 168gr Match Kings. Hard to justify the cost when I'm not shooting a match. Anyway, I would appreciate your thoughts on this subject.
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3 comments

Date Votes
  • BGHillbilly
    Did you not have any elevation change with the 3 loads?
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  • gunprofit
    Actually the elevation change is less than the latteral change. Elevation difference is less than 2". Tried researching this on the web but haven't found any good explaination. I'm baffled.
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  • bpost
    quote:Originally posted by gunprofit
    Actually the elevation change is less than the latteral change. Elevation difference is less than 2". Tried researching this on the web but haven't found any good explaination. I'm baffled.


    Barrel harmonics would account for that difference.
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