A simple function can kill all by number (though it barfs on errors)
kill_hist() {
for i in $(echo $@ | sed -e 's/ /\n/g;' | sort -rn | sed -e 's/\n/ /;')
do
history -d $i;
done
}
kill_hist `seq 511 520`
# or kill a few ranges
kill_hist `seq 1001 1010` `seq 1200 1201`