Rifle zeroed. Travel several hundred miles North (by train). On arrival, check zero. Bullet MPI low: 2 x 1cm clicks ‘up’ required. Successfully conduct hunting trip using comeup chart –but adding 2 clicks ‘up’ to all elevations. Return home. Check zero this afternoon. Rifle back to original zero (ie 2 additional clicks no longer required). But….(and I know what you’re all thinking)…..both the Northern zero and the home zero were conducted at roughly the same altitude (within 20m) at roughly the same temp (around 8 degrees C). I can’t explain this! /ubbthreads/images/graemlins/confused.gif Any ideas?