I feel this is probably is already known, but figured i would post it anyway. Iron sights sit higher as if misaligned on all guns compared to stable branch. Readjusting by zeroing them reverts them to their previous state as in stable. This happens has to be done each time you die and respawn, requiring me to adjust the zeroing to ensure accurate ranging after each death. I have seen it on most if not all weapons from AK's to M16's and the MG's inbetween.