Its wierd but I have this problem too. Usually, a couple weeks before the season I break out some broadheads and shoot. I usually group right with my broadheads. Ishot today, and couldn't believe what I saw. First 2 shots at 20 were fine, one broadhead and one field point, hit dead on. Moved to 30 and my first arrow fishtailed and took a dive, hit about 6-7 inches low at 30. My next arrow was a field point, it hit dead on. 3rd arrow, another broadhead. It grouped with my field point. Changed heads a couple times, now I have 2 arrows that shoot dead on withbroadheads and 2 that dont. I've got about 2 weeks to the season, and I ran out of time at the range. Had told a land owner I was coming by this afternoon to hang a stand, I didn't wanna not show up. I've got a little more work to do before I'll feel comfortable this season.