I've got a scoped TC and had it sighted in dead on at 70yds, on a 80 deg day. I went out and shot the gun again on a 40 deg day and my point of impact was 2 in. high, it was dead center Left to Right just high. I resighted in to be dead on at 70yds again. Is this common? If it ends up being 20 deg. when season opens do you think I,ll have to sight in again. Thanks.