How about a hash slice? No sorting required.

johngg@abouriou:~$ perl -Mstrict -Mwarnings -E 'say q{};
my @PCHR = qw{ K Q R B N P };
my $w1   =  q{QRKPNB};
my %w1LU = map { $_ => $_ } split m{}, $w1;
say join q{}, @w1LU{ @PCHR };'

KQRBNP
[download]

I hope this is of interest.