Using a spotter and bullet trace it's relatively easy to get onto target however from our recent shooting session we were unable to compensate for small amounts. For example shooting at 300 or 500m we weren't able to see bullet holes due to severe mirage and sun in the face however bullet trace was nicely seen. We were on paper (after we checked the targets) and a nice group in lower right (approx 10cm@5 o'clock) however when calling shots from bullet trace all were called center on (spotter was 10m behind the shooter to the right approx 2m). On other occasion two spotters were one the right and one to the left and the left spotter observed high and left and right spotter observed low and righ
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Are there any rules regarding spotting (i'd assume best position is directly behind the shooter not offset and looking above - which would also mean that trace will disappear slightly above target) and helping with bullet trace to aid in centering groups.

Are there any rules regarding spotting (i'd assume best position is directly behind the shooter not offset and looking above - which would also mean that trace will disappear slightly above target) and helping with bullet trace to aid in centering groups.