diff --git a/CosmicReco/src/LineFinder_module.cc b/CosmicReco/src/LineFinder_module.cc
index c596ed079..83b06f9c3 100644
--- a/CosmicReco/src/LineFinder_module.cc
+++ b/CosmicReco/src/LineFinder_module.cc
@@ -77,7 +77,7 @@ namespace mu2e{
 
       ProditionsHandle<Tracker> _alignedTracker_h;
 
-      int findLine(const ComboHitCollection& shC, art::Event const& event, CosmicTrackSeed &tseed);
+      int findLine(const ComboHitCollection& shC, std::vector<StrawHitIndex> const& shiv, art::Event const& event, CosmicTrackSeed& tseed);
   };
 
 
@@ -112,24 +112,18 @@ void LineFinder::produce(art::Event& event ) {
 
   for (size_t index=0;index< tccol.size();++index) {
     const auto& tclust = tccol[index];
+    std::vector<StrawHitIndex> shiv;
+    // get collection at straw level
+    auto chcp = chcol.fillStrawHitIndices(tclust.hits(),shiv,StrawIdMask::uniquestraw);
+    auto chc = *chcp;
 
-    // convert (presumably) panel hits in time clusterto straw hits
     CosmicTrackSeed tseed;
-    ComboHitCollection tchits;
-    tchits.reserve(tclust.hits().size()*2); // guess 2 straw hits/panel hit
-
-    int nhits = 0;
-    ComboHitCollection::CHCIter chids;
-    chcol.fillComboHits( tclust.hits(), chids);
-    for (auto const& it : chids){
-      tchits.push_back(*it);
-      nhits += it->nStrawHits();
-    }
+    tseed._straw_chits.setAsSubset(chH,StrawIdMask::uniquestraw);
 
     tseed._timeCluster = art::Ptr<TimeCluster>(tcH,index);
     tseed._track.converged = true;
 
-    int seedSize = findLine(tchits, event, tseed);
+    int seedSize = findLine(chc, shiv, event, tseed);
     if (_diag > 1)
       std::cout << "LineFinder: seedSize = " << seedSize << std::endl;
 
@@ -148,7 +142,7 @@ void LineFinder::produce(art::Event& event ) {
   event.put(std::move(seed_col));
 }
 
-int LineFinder::findLine(const ComboHitCollection& shC, art::Event const& event, CosmicTrackSeed& tseed){
+int LineFinder::findLine(const ComboHitCollection& shC, std::vector<StrawHitIndex> const& shiv, art::Event const& event, CosmicTrackSeed& tseed){
 
   //mu2e::GeomHandle<mu2e::Tracker> th;
   auto tracker = _alignedTracker_h.getPtr(event.id());//th.get();
@@ -160,18 +154,20 @@ int LineFinder::findLine(const ComboHitCollection& shC, art::Event const& event,
 
   bool found_all = false;
   // lets get the best pairwise vector
-  for (size_t i=0;i<shC.size();i++){
+  for (size_t i=0;i<shiv.size();i++){
+    size_t iloc = shiv[i];
     if (found_all)
       break;
-    Straw const& strawi = tracker->getStraw(shC[i].strawId());
-    for (size_t j=i+1;j<shC.size();j++){
+    Straw const& strawi = tracker->getStraw(shC[iloc].strawId());
+    for (size_t j=i+1;j<shiv.size();j++){
+      size_t jloc = shiv[j];
       if (found_all)
         break;
-      Straw const& strawj = tracker->getStraw(shC[j].strawId());
+      Straw const& strawj = tracker->getStraw(shC[jloc].strawId());
       for (int is=-1*_Nsteps;is<_Nsteps+1;is++){
-        CLHEP::Hep3Vector ipos = shC[i].posCLHEP() + strawi.getDirection()*shC[i].wireRes()*_stepSize*is;
+        CLHEP::Hep3Vector ipos = shC[iloc].posCLHEP() + strawi.getDirection()*shC[iloc].wireRes()*_stepSize*is;
         for (int js=-1*_Nsteps;js<_Nsteps+1;js++){
-          CLHEP::Hep3Vector jpos = shC[j].posCLHEP() + strawj.getDirection()*shC[j].wireRes()*_stepSize*js;
+          CLHEP::Hep3Vector jpos = shC[jloc].posCLHEP() + strawj.getDirection()*shC[jloc].wireRes()*_stepSize*js;
 
           CLHEP::Hep3Vector newdir = (jpos-ipos).unit();
           CLHEP::Hep3Vector icross = (jpos-ipos).cross(strawi.getDirection()).unit();
@@ -184,17 +180,18 @@ int LineFinder::findLine(const ComboHitCollection& shC, art::Event const& event,
               // now loop over all hits and see how many are in this track
               int count = 0;
               double ll = 0;
-              for (size_t k=0;k<shC.size();k++){
-                Straw const& strawk = tracker->getStraw(shC[k].strawId());
+              for (size_t k=0;k<shiv.size();k++){
+                size_t kloc = shiv[k];
+                Straw const& strawk = tracker->getStraw(shC[kloc].strawId());
                 TwoLinePCA pca( strawk.getMidPoint(), strawk.getDirection(),
                     ipos, newdir);
                 double dist = (pca.point1()-strawk.getMidPoint()).mag();
                 if (pca.dca() < _maxDOCA && dist < strawk.halfLength()){
                   count += 1;
-                  ll += pow(dist-shC[k].wireDist(),2)/shC[k].wireVar();
+                  ll += pow(dist-shC[kloc].wireDist(),2)/shC[kloc].wireVar();
                 }
               }
-              if (count == (int) shC.size())
+              if (count == (int) shiv.size())
                 found_all = true;
               if (count > bestcount || (count == bestcount && ll < bestll)){
                 bestcount = count;
@@ -219,17 +216,20 @@ int LineFinder::findLine(const ComboHitCollection& shC, art::Event const& event,
 
   double avg_t0 = 0;
   int good_hits = 0;
-  for (size_t k=0;k<shC.size();k++){
-    Straw const& strawk = tracker->getStraw(shC[k].strawId());
+  for (size_t k=0;k<shiv.size();k++){
+    size_t kloc = shiv[k];
+    Straw const& strawk = tracker->getStraw(shC[kloc].strawId());
     TwoLinePCA pca( strawk.getMidPoint(), strawk.getDirection(),
         seedInt, seedDir);
     double dist = (pca.point1()-strawk.getMidPoint()).dot(strawk.getDirection());
     if (pca.dca() < _maxDOCA && fabs(dist) < strawk.halfLength()){
       double traj_time = ((pca.point2() - seedInt).dot(seedDir))/299.9;
-      double hit_t0 = shC[k].time() - shC[k].driftTime() - shC[k].propTime() - traj_time;
+      double hit_t0 = shC[kloc].time() - shC[kloc].driftTime() - shC[kloc].propTime() - traj_time;
       avg_t0 += hit_t0;
       good_hits++;
-      tseed._straw_chits.push_back(shC[k]);
+      ComboHit combohit;
+      combohit.init(shC[kloc],kloc);
+      tseed._straw_chits.push_back(std::move(combohit));
     }
   }
   avg_t0 /= good_hits;
@@ -258,22 +258,6 @@ int LineFinder::findLine(const ComboHitCollection& shC, art::Event const& event,
   tseed._track.SetFitEquation(XYZTrack);
   tseed._track.SetMinuitEquation(XYZTrack);
 
-  // For compatibility FIXME
-  for(size_t ich= 0; ich<tseed._straw_chits.size(); ich++){
-    std::vector<StrawHitIndex> shitids;
-    tseed._straw_chits.fillStrawHitIndices(ich, shitids);
-
-    /*
-    for(auto const& ids : shitids){
-      size_t    istraw   = (ids);
-      TrkStrawHitSeed tshs;
-      tshs._index  = istraw;
-      tshs._t0 = tseed._t0;
-      tseed._trkstrawhits.push_back(tshs);
-    }
-    */
-  }
-
   return good_hits;
 }
 
diff --git a/RecoDataProducts/inc/ComboHit.hh b/RecoDataProducts/inc/ComboHit.hh
index 7c9597d11..e4d009a87 100644
--- a/RecoDataProducts/inc/ComboHit.hh
+++ b/RecoDataProducts/inc/ComboHit.hh
@@ -150,15 +150,16 @@ namespace mu2e {
       // This function is called recursively, so the the vector must be empty on the top-most call
 #ifndef __ROOTCLING__
       // find the parent at a given level
-      CHCPTR parent(StrawIdMask::Level level) const;
-      void fillStrawDigiIndices( size_t chindex, SHIV& shids) const;
+      // if parent and grandparent are the same level, will select the grandparent unless stopatfirst set
+      CHCPTR parent(StrawIdMask::Level level, bool stopatfirst=false) const;
+      void fillStrawDigiIndices( size_t chindex, SHIV& shids, bool stopatfirst=false) const;
       // Fill indices to the specified level.  Return value is the collection to whic
       // the indices apply.  first, given all my hits
-      ComboHitCollection const* fillStrawHitIndices( SHIV& shiv, StrawIdMask::Level clevel=StrawIdMask::uniquestraw) const;
+      ComboHitCollection const* fillStrawHitIndices( SHIV& shiv, StrawIdMask::Level clevel=StrawIdMask::uniquestraw, bool stopatfirst=false) const;
       // given a specific hit (index) in myself
-      ComboHitCollection const* fillStrawHitIndices( size_t chindex, SHIV& shiv, StrawIdMask::Level clevel=StrawIdMask::uniquestraw) const;
+      ComboHitCollection const* fillStrawHitIndices( size_t chindex, SHIV& shiv, StrawIdMask::Level clevel=StrawIdMask::uniquestraw, bool stopatfirst=false) const;
       // given a vector of indices
-      ComboHitCollection const* fillStrawHitIndices(SHIV const& inshiv, SHIV& outshiv, StrawIdMask::Level clevel=StrawIdMask::uniquestraw) const;
+      ComboHitCollection const* fillStrawHitIndices(SHIV const& inshiv, SHIV& outshiv, StrawIdMask::Level clevel=StrawIdMask::uniquestraw, bool stopatfirst=false) const;
       // the following are deprecated in favor of the more-efficient and self-checking functions above
       // translate a collection of ComboHits into the lowest-level (straw) combo hits.  This function is recursive
       void fillComboHits( std::vector<uint16_t> const& indices, CHCIter& iters) const;
@@ -171,6 +172,16 @@ namespace mu2e {
       void setParent(CHCPTR const& parent);
       // or set to be the same as another collection
       void setSameParent(ComboHitCollection const& other);
+      // if argument has its own parent, set this parent to match.
+      // otherwise set this parent to be collection in argument
+      void setAsSubset(CHCPTR const& other);
+      void setAsSubset(art::Handle<ComboHitCollection> const& ohandle);
+      void setAsSubset(art::ValidHandle<ComboHitCollection> const& ohandle);
+      // optionally specify what level to make as parent
+      // if parent and grandparent are the same level, will select the grandparent unless stopatfirst set
+      void setAsSubset(CHCPTR const& optr, StrawIdMask::Level level, bool stopatfirst=false);
+      void setAsSubset(art::Handle<ComboHitCollection> const& ohandle, StrawIdMask::Level level, bool stopatfirst=false);
+      void setAsSubset(art::ValidHandle<ComboHitCollection> const& ohandle, StrawIdMask::Level level, bool stopatfirst=false);
 #endif
       // accessors
       auto const& parent() const { return _parent; }
diff --git a/RecoDataProducts/src/ComboHit.cc b/RecoDataProducts/src/ComboHit.cc
index 6d85a1322..b3cba2f5c 100644
--- a/RecoDataProducts/src/ComboHit.cc
+++ b/RecoDataProducts/src/ComboHit.cc
@@ -49,17 +49,59 @@ namespace mu2e {
 
 #ifndef __ROOTCLING__
 
-  ComboHitCollection::CHCPTR ComboHitCollection::parent(StrawIdMask::Level level) const {
+  ComboHitCollection::CHCPTR ComboHitCollection::parent(StrawIdMask::Level level, bool stopatfirst) const {
     auto retval = _parent;
-    if(_parent.refCore().isNull() || level == this->level()){
+    if(_parent.refCore().isNull()){
       throw cet::exception("RECO")<<"mu2e::ComboHitCollection: no such parent" << std::endl;
     } else {
       // recursive call
-      if(retval->level() != level) retval = _parent->parent(level);
+      if (retval->level() != level || (!stopatfirst && retval->parent().refCore().isNonnull() && retval->parent()->level() == level)){
+        retval = _parent->parent(level);
+      }
     }
     return retval;
   }
 
+  void ComboHitCollection::setAsSubset(art::Handle<ComboHitCollection> const& ohandle){
+    if (ohandle.isValid()){
+      auto optr = CHCPTR(ohandle);
+      setAsSubset(optr);
+    } else {
+      throw cet::exception("RECO")<<"mu2e::ComboHitCollection: invalid handle" << std::endl;
+    }
+  }
+  void ComboHitCollection::setAsSubset(art::ValidHandle<ComboHitCollection> const& ohandle){
+    auto optr = CHCPTR(ohandle);
+    setAsSubset(optr);
+  }
+  void ComboHitCollection::setAsSubset(CHCPTR const& other){
+    _parent = other->parent();
+    if (_parent.refCore().isNull()){
+      _parent = other;
+    }
+  }
+
+  void ComboHitCollection::setAsSubset(art::ValidHandle<ComboHitCollection> const& ohandle, StrawIdMask::Level level, bool stopatfirst){
+    if (ohandle.isValid()){
+      auto optr = CHCPTR(ohandle);
+      setAsSubset(optr,level,stopatfirst);
+    } else {
+      throw cet::exception("RECO")<<"mu2e::ComboHitCollection: invalid handle" << std::endl;
+    }
+  }
+  void ComboHitCollection::setAsSubset(art::Handle<ComboHitCollection> const& ohandle, StrawIdMask::Level level, bool stopatfirst){
+    auto optr = CHCPTR(ohandle);
+    setAsSubset(optr,level,stopatfirst);
+  }
+  void ComboHitCollection::setAsSubset(CHCPTR const& optr, StrawIdMask::Level level, bool stopatfirst){
+    if (optr->level() == level && (stopatfirst || optr->parent().refCore().isNull() || optr->parent()->level() != level)){
+      _parent = optr;
+    }else{
+      _parent = optr->parent(level,stopatfirst);
+    }
+  }
+
+
   void ComboHitCollection::setSameParent(ComboHitCollection const& other) { _parent = other.parent(); }
   void ComboHitCollection::setParent(CHCPTR const& parent) { _parent = parent; }
 
@@ -75,10 +117,10 @@ namespace mu2e {
     _parent = CHCPTR(phandle);
   }
 
-  void ComboHitCollection::fillStrawDigiIndices(size_t chindex, vector<StrawDigiIndex>& shiv) const {
+  void ComboHitCollection::fillStrawDigiIndices(size_t chindex, vector<StrawDigiIndex>& shiv, bool stopatfirst) const {
     // if this is a straw-level ComboHit, get the digi index
     ComboHit const& ch = this->at(chindex);
-    if(level() == StrawIdMask::uniquestraw) {
+    if(level() == StrawIdMask::uniquestraw && (stopatfirst || _parent.refCore().isNull() || _parent->level() != StrawIdMask::uniquestraw)){
       shiv.push_back(ch.index(0));
       // if this collection references a sub-collection, go down recursively
     } else if(_parent.refCore().isNonnull()){
@@ -90,9 +132,9 @@ namespace mu2e {
     }
   }
 
-  ComboHitCollection const* ComboHitCollection::fillStrawHitIndices( size_t chindex, SHIV& shiv, StrawIdMask::Level clevel) const {
+  ComboHitCollection const* ComboHitCollection::fillStrawHitIndices( size_t chindex, SHIV& shiv, StrawIdMask::Level clevel, bool stopatfirst) const {
     ComboHitCollection const* retval = this;
-    if(level() == clevel){
+    if(level() == clevel && (stopatfirst || _parent.refCore().isNull() || _parent->level() != clevel)){
       shiv.push_back(chindex);
       // if this collection references other collections, go down recursively
     } else if(_parent.refCore().isNonnull()){
@@ -117,9 +159,9 @@ namespace mu2e {
     return retval;
   }
 
-  ComboHitCollection const* ComboHitCollection::fillStrawHitIndices(SHIV const& inshiv, SHIV& outshiv, StrawIdMask::Level clevel) const {
+  ComboHitCollection const* ComboHitCollection::fillStrawHitIndices(SHIV const& inshiv, SHIV& outshiv, StrawIdMask::Level clevel, bool stopatfirst) const {
     ComboHitCollection const* retval = this;
-    if(level() == clevel){
+    if(level() == clevel && (stopatfirst || _parent.refCore().isNull() || _parent->level() != clevel)){
       outshiv = inshiv;
     } else if(_parent.refCore().isNonnull()){
       if(_parent->level() == clevel){
@@ -149,10 +191,10 @@ namespace mu2e {
     return retval;
   }
 
-  ComboHitCollection const* ComboHitCollection::fillStrawHitIndices( SHIV& shiv, StrawIdMask::Level clevel) const {
+  ComboHitCollection const* ComboHitCollection::fillStrawHitIndices( SHIV& shiv, StrawIdMask::Level clevel, bool stopatfirst) const {
     shiv.clear();
     const ComboHitCollection* retval = this;
-    if(level() == clevel){
+    if(level() == clevel && (stopatfirst || _parent.refCore().isNull() || _parent->level() != clevel)){
       shiv.reserve(this->size());
       for(size_t iind = 0;iind < this->size(); ++iind)shiv.push_back(iind);
       // if this collection references other collections, go down recursively