I have shot 3 otters with a 410 shotgun and none of them went under. They thrashed around a little and just stayed floating on the surface. Paddle out in my little boat and scoop them up.Yours may show up floating soon.
Both otters reacted when I shot and then disappeared. The 50gr ballistic tip is a pretty explosive bullet so could be it blew out the lungs. I motored around in my boat this afternoon quite a bit and saw no sign of otter. I have a lot of confidence in the rifle and round - very accurate.
