I have fired about 50 rounds through my Cooper in 280AI,and I finally found a load that will meet the 1/2" at 100 yards accuracy guarantee.I fired three groups this morning using the 140gr barnes TTSX ahead of 59gr of imr-4831,and the first group out of a clean barrel went into 3/4".The second group went into 1/2",and the third group into just over 3/8".All nine rounds went into 1",and if the first shot out of a clean barrel is ignored,the next 8 shots went into 3/4".My chronograph battery died just as I started shooting,but the two shots that were recorded were right around 3100fps.I am going to load some more rounds,fire a few more groups,and chronograph the loads,but I am thinking that my load development is complete.
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