My son has a Mossberg ATR 100 synthetic (no wise cracks please). We are trying to do some load development with 165 gr bullets for elk hunting. Son replaced the scope with a Nikon from a cheap Bushnell and Weaver rings with a one piece DNZ ring & base in the process. The gun has been shooting 1 1/4 groups routinely. Now all of a sudden the gun will shoot 2 rounds touching then flings the next round 2-3" out of the group. We went back to his old scope same results. My thoughts are to check the bedding, terminal clean the gun??? I'm lost other than that, tried different shooters same results..Gun has maybe 600 rounds through it???

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