I recently zeroed in my 30-06 and have begun to wonder if I might have thrown off the point of impact in the way I rested the fore-end. I raised the front sandbag by setting it on a couple of 2x6 boards which were themselves placed on a sturdy, wood table. As I've thought about it, I wonder if the hard surfaces of the those boards/table in contact with each other might have thrown off the zero.

Do you think I have a reliable point of impact?

The actual zeroing session was utterly routine and as simple as it gets. My rifle shot its typical one inch group an inch high, I adjusted the scope down, and the next group was exactly where I wanted it. No flyers or anything unusual.