No idea since homicide by drowning is notoriously hard to prove[0], but the median pool is more likely to drown someone than the median "assault weapon" is to kill someone.
~10 million swimming pools in the US vs. ~20 million "assault weapons," and there are fewer murders annually with long guns of all types (of which "assault weapons" are a small subset) than there are pool drownings. Also pools disproportionately kill kids, while most victims of gun violence ate adults.
