diff --git a/CHANGES.md b/CHANGES.md
index 5b61995..d3a7ab9 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,5 +1,12 @@
 # CHANGES
 
+## 5.2.0
+
+* Expose option for "legacy" to allow for <=5.0.5 processing methods.
+  * `bamtofastq` when pulling reads from BAM/CRAM input.
+  * `bammarkduplicates2` for duplicate marking.
+  * Affects `bwa_mem.pl` and `merge_or_mark.pl`
+
 ## 5.1.0
 
 * Base image updated to Focal (Ubuntu 20.04).
diff --git a/Dockerfile b/Dockerfile
index c112cfa..8265e02 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -62,7 +62,7 @@ FROM  ubuntu:20.04
 
 LABEL maintainer="cgphelp@sanger.ac.uk"\
       uk.ac.sanger.cgp="Cancer, Ageing and Somatic Mutation, Wellcome Sanger Institute" \
-      version="5.1.0" \
+      version="5.2.0" \
       description="pcap-core"
 
 ENV OPT /opt/wtsi-cgp
diff --git a/bin/bwa_mem.pl b/bin/bwa_mem.pl
index 6f7afe4..0bab214 100755
--- a/bin/bwa_mem.pl
+++ b/bin/bwa_mem.pl
@@ -136,6 +136,7 @@ sub setup {
               'qf|mmqcfrac:f' => \$opts{'mmqcfrac'},
               'bm2|bwamem2' => \$opts{'bwamem2'},
               'd|dupmode:s' => \$opts{'dupmode'},
+              'legacy' => \$opts{'legacy'},
               'ss|seqslice:i' => $opts{'seqslice'},
   ) or pod2usage(2);
 
@@ -178,6 +179,11 @@ sub setup {
   delete $opts{'mmqc'} unless(defined $opts{'mmqc'});
   delete $opts{'csi'} unless(defined $opts{'csi'});
   delete $opts{'bwamem2'} unless(defined $opts{'bwamem2'});
+  delete $opts{'legacy'} unless(defined $opts{'legacy'});
+
+  if(defined $opts{'bwamem2'} && defined $opts{'legacy'}) {
+    warn "WARN: Use of options bwamem2 and legacy is suboptimal, proceeding but memory will be excessive.\n";
+  }
 
   PCAP::Cli::opt_requires_opts('scramble', \%opts, ['cram']);
 
@@ -243,7 +249,7 @@ =head1 SYNOPSIS
     -threads     -t    Number of threads to use. [1]
 
   Optional parameters:
-    -bwamem2     -bm2  Use bwa-mem2 instead of bwa.
+    -bwamem2     -bm2  Use bwa-mem2 instead of bwa (experimental).
     -fragment    -f    Split input into fragments of X million repairs [10]
                         - only applies to fastq[.gz] input
     -nomarkdup   -n    Don't mark duplicates [flag]
@@ -261,6 +267,10 @@ =head1 SYNOPSIS
                         - Please see 'bwa_mem.pl -m'
     -mmqcfrac    -qf   Mismatch fraction for -mmqc [0.05]
     -dupmode     -d    see "samtools markdup -m" [t]
+    -legacy            Equivalent to PCAP-core<=5.0.5
+                        - bamtofastq instead of samtools collate (for BAM/CRAM input)
+                        - dupmode ignored as uses bammarkduplicates2
+                        - Avoid use with bwamem2 (memory explosion)
 
   Targeted processing:
     -process     -p    Only process this step then exit, optionally set -index
@@ -360,6 +370,16 @@ =head2 OPTIONAL parameters
 
 Disables duplicate marking, switching bammarkduplicates2 for bammerge.
 
+=item B<-dupmode>
+
+Switch between template and sequence based marking.  See "samtools markdup" man page for more details
+
+=item B<-legacy>
+
+Processing equivalent to versions of PCAP-core <= 5.0.5 (bamtofastq + bammarkduplicates2)
+
+Not recommended with bwamem2 - memory explosions.
+
 =item B<-csi>
 
 User CSI style index for final BAM file instead of default BAI.
diff --git a/bin/merge_or_mark.pl b/bin/merge_or_mark.pl
index a87c48f..f5b0cc2 100755
--- a/bin/merge_or_mark.pl
+++ b/bin/merge_or_mark.pl
@@ -90,6 +90,7 @@ sub setup {
               'c|cram' => \$opts{'cram'},
               'sc|scramble=s' => \$opts{'scramble'},
               'd|dupmode:s' => \$opts{'dupmode'},
+              'legacy' => \$opts{'legacy'},
               'ss|seqslice:i' => $opts{'seqslice'},
   ) or pod2usage(2);
 
@@ -121,6 +122,7 @@ sub setup {
 
   delete $opts{'process'} unless(defined $opts{'process'});
   delete $opts{'index'} unless(defined $opts{'index'});
+  delete $opts{'legacy'} unless(defined $opts{'legacy'});
   delete $opts{'scramble'};
   delete $opts{'csi'} unless(defined $opts{'csi'});
   if($opts{'qnamesort'} && !$opts{'nomarkdup'}){
@@ -183,7 +185,8 @@ =head1 SYNOPSIS
     -cram        -c   Output cram, see '-sc' [flag]
     -seqslice    -ss   seqs_per_slice for CRAM compression [samtools default: 10000]
     -scramble    -sc   DEPRECATED
-    -dupmode     -d    see "samtools markdup -m" [t]
+    -dupmode     -d    See "samtools markdup -m" [t]
+    -legacy            Use legacy bammarkduplicates2, ignores '-dupmode'
 
   Targeted processing:
     -process     -p   Only process this step then exit
diff --git a/lib/PCAP.pm b/lib/PCAP.pm
index d75980c..817557c 100644
--- a/lib/PCAP.pm
+++ b/lib/PCAP.pm
@@ -28,7 +28,7 @@ use FindBin qw($Bin);
 use File::Which qw(which);
 # don't use autodie, only core perl in here
 
-our $VERSION = '5.1.0';
+our $VERSION = '5.2.0';
 our @EXPORT = qw($VERSION _which);
 
 const my $LICENSE =>
diff --git a/lib/PCAP/Bam.pm b/lib/PCAP/Bam.pm
index 19ba85b..4cce3f1 100644
--- a/lib/PCAP/Bam.pm
+++ b/lib/PCAP/Bam.pm
@@ -154,8 +154,21 @@ sub merge_or_mark_lanes {
   else {
     my $merge    = sprintf q{%s merge -u -@ %d - %s},
                            $tools{samtools}, $helper_threads, $input_str;
-    my $markdup  = sprintf q{%s markdup --mode %s --output-fmt bam,level=0 -S --include-fails -T %s -@ %d -f %s.met - -},
+    my $markdup;
+    if(exists $options->{legacy}) {
+      my $mmflagmod = _which('mmFlagModifier') || die "Unable to find 'mmFlagModifier' in path";
+      my $bammarkdups = _which('bammarkduplicates2') || die "Unable to find 'bammarkduplicates2' in path";
+
+      my $mmQcRemove = sprintf '%s --remove -l 0 -@ %d', $mmflagmod, $helper_threads;
+      my $bammarkdup = sprintf '%s tmpfile=%s M=%s.met level=0 markthreads=%d', $bammarkdups, $strmd_tmp, $marked, $helper_threads;
+      my $mmQcReplace = sprintf '%s --replace -l 0 -@ %d', $mmflagmod, $helper_threads;
+
+      $markdup = sprintf q{%s | %s | %s}, $mmQcRemove, $bammarkdup, $mmQcReplace;
+    }
+    else {
+      $markdup  = sprintf q{%s markdup --mode %s --output-fmt bam,level=0 -S --include-fails -T %s -@ %d -f %s.met - -},
                            $tools{samtools}, $options->{dupmode}, $strmd_tmp, $helper_threads, $marked;
+    }
     my $compress = sprintf q{%s view -T %s --output-fmt %s -@ %d -},
                            $tools{samtools}, $options->{reference}, $out_fmt, $helper_threads;
     my $idx      = sprintf q{%s index -@ %d %s - %s.%s},
@@ -254,8 +267,21 @@ sub merge_and_mark_dup {
   else {
     my $merge    = sprintf q{%s merge -u -@ %d - %s},
                            $tools{samtools}, $helper_threads, $input_str;
-    my $markdup  = sprintf q{%s markdup --mode %s --output-fmt bam,level=0 -S --include-fails -T %s -@ %d -f %s.met - -},
+    my $markdup;
+    if(exists $options->{legacy}) {
+      my $mmflagmod = _which('mmFlagModifier') || die "Unable to find 'mmFlagModifier' in path";
+      my $bammarkdups = _which('bammarkduplicates2') || die "Unable to find 'bammarkduplicates2' in path";
+
+      my $mmQcRemove = sprintf '%s --remove -l 0 -@ %d', $mmflagmod, $helper_threads;
+      my $bammarkdup = sprintf '%s tmpfile=%s M=%s.met level=0 markthreads=%d', $bammarkdups, $strmd_tmp, $marked, $helper_threads;
+      my $mmQcReplace = sprintf '%s --replace -l 0 -@ %d', $mmflagmod, $helper_threads;
+
+      $markdup = sprintf q{%s | %s | %s}, $mmQcRemove, $bammarkdup, $mmQcReplace;
+    }
+    else {
+      $markdup  = sprintf q{%s markdup --mode %s --output-fmt bam,level=0 -S --include-fails -T %s -@ %d -f %s.met - -},
                            $tools{samtools}, $options->{dupmode}, $strmd_tmp, $helper_threads, $marked;
+    }
     my $compress = sprintf q{%s view -T %s --output-fmt %s -@ %d -},
                            $tools{samtools}, $options->{reference}, $out_fmt, $helper_threads;
     my $idx      = sprintf q{%s index -@ %d %s - %s.%s},
diff --git a/lib/PCAP/Bwa.pm b/lib/PCAP/Bwa.pm
index a963fb9..048d60a 100644
--- a/lib/PCAP/Bwa.pm
+++ b/lib/PCAP/Bwa.pm
@@ -214,9 +214,19 @@ sub split_in {
       my $samtools = _which('samtools') || die "Unable to find 'samtools' in path";
       my $mmQcStrip = sprintf '%s --remove -l 0 -@ %d -i %s', _which('mmFlagModifier'), $helpers, $input->in;
       my $view = sprintf '%s view %s -bu -T %s -F 2816 -@ %d -', $samtools, $TAG_STRIP, $options->{'reference'}, $helpers; # leave
-      my $collate = sprintf '%s collate -Ou -@ %d - %s/collate', $samtools, $helpers, $collate_folder;
-      my $split = sprintf '%s split --output-fmt bam,level=1 -@ %d -u %s/unknown.bam -f %s/%%!_i.bam -', $samtools, $helpers, $split_folder, $split_folder;
-      my $cmd = sprintf '%s | %s | %s | %s', $mmQcStrip, $view, $collate, $split;
+      my $collate_split;
+      if(exists $options->{legacy}) {
+        my $bamtofastq = _which('bamtofastq') || die "Unable to find 'bamtofastq' in path";
+        $collate_split = sprintf '%s exclude=QCFAIL,SECONDARY,SUPPLEMENTARY tryoq=1 gz=1 level=1 outputperreadgroup=1 outputperreadgroupsuffixF=_i.fq outputperreadgroupsuffixF2=_i.fq T=%s/bamtofastq outputdir=%s split=%s',
+                                 $bamtofastq, $collate_folder, $split_folder,
+                                 $fragment_size * $MILLION * $BAM_MULT;
+      }
+      else {
+        my $collate = sprintf '%s collate -Ou -@ %d - %s/collate', $samtools, $helpers, $collate_folder;
+        my $split = sprintf '%s split --output-fmt bam,level=1 -@ %d -u %s/unknown.bam -f %s/%%!_i.bam -', $samtools, $helpers, $split_folder, $split_folder;
+        $collate_split = sprintf '%s | %s', $collate, $split;
+      }
+      my $cmd = sprintf '%s | %s | %s', $mmQcStrip, $view, $collate_split;
       # treat as interleaved fastq
       push @commands, 'set -o pipefail';
       push @commands, $cmd;
@@ -314,9 +324,15 @@ sub bwa_mem {
       }
     }
     else {
-      # bam/cram
-      my $tofastq = sprintf '%s fastq -@ %d -N %s', $tools{samtools}, $threads, $split;
-      $bwa = sprintf '%s | %s /dev/stdin', $tofastq, $bwa;
+      # due to legacy processing need to handle bam or fastq input here
+      if($split =~ m/\.gz$/) {
+        $bwa .= ' '.$split;
+      }
+      else {
+        # bam/cram
+        my $tofastq = sprintf '%s fastq -@ %d -N %s', $tools{samtools}, $threads, $split;
+        $bwa = sprintf '%s | %s /dev/stdin', $tofastq, $bwa;
+      }
     }
 
     my $sorted_bam_stub = $split;