I'm starting to wonder if the way I was holding the rifle is the culprit. This is really the only thing that I consciously recalled being different. At the time I didn't think it'd make a dern. I was using sandbags both times, but, on the second trip, the way the bench was sized, it was easier (and noticeably more stable) for me to not have my forward hand holding the forearm.
I suspect that you have just answered your question. However, like 5sdad posted, sometimes it just happens. Phase of the moon, too much coffee, fight with the wife, bad day at work, etc.................
