User blog comment:Xilinoc/Ch. 575 - THE KILLERS HIGH/@comment-14244059-20140403071431/@comment-4207271-20140403102205

As stated at the start of the series, only Spirit Weapons can harm Shinigami (technically, it was stated Zanpakuto, but they are a type of spirit weapon), so the guns are likely Quincy Guns, like Commissioner Gordon, BG9, and someone else im forgetting