I am running two geometries; both are 2 mm thick plastic disks, one defined in gdml and the other using MiceModules. I get a nice distribution of secondary electrons with the MiceModules, but nothing with the gdml. A few observations:

1. The code at src/common_cpp/Simulation/MAUSGeant4Manager.hh,cc does not set the user limits correctly. The SetVolumeInformation function doesn't work. I fixed this, and manually set the Min Kinetic Energy to be low (1 keV). Still no deltas
2. The ProductionThreshold is set to be "very high" during the cavity phasing part of the G4 setup - see Simulation/MAUSPhysicsList.hh,cc. I can't see at the moment how it is set back to something sensible. Presumably it is somewhere...

Continuing to dig.

This patch seems to have fixed things:

=== modified file 'src/common_cpp/Simulation/MAUSPhysicsList.cc'
--- src/common_cpp/Simulation/MAUSPhysicsList.cc        2016-08-31 11:59:03 +0000
+++ src/common_cpp/Simulation/MAUSPhysicsList.cc        2018-03-23 18:32:42 +0000
@@ -181,8 +181,7 @@
       break;
   }
   std::vector<std::string> uiCommand;
-  if (eLossModel != energyStraggling)
-    uiCommand.push_back("/run/setCut "+STLUtils::ToString(cutDouble));
+  uiCommand.push_back("/run/setCut "+STLUtils::ToString(cutDouble));
   uiCommand.push_back("/process/eLoss/fluct "+flucActive);
   for (int i = 0; i < _nELossNames; i++)
     uiCommand.push_back("/process/"+elossActive+" "+_eLossNames[i]);

This is the patch to get proper propagation of user limits

=== modified file 'src/common_cpp/Simulation/MAUSGeant4Manager.cc'
--- src/common_cpp/Simulation/MAUSGeant4Manager.cc      2016-08-31 11:59:03 +0000
+++ src/common_cpp/Simulation/MAUSGeant4Manager.cc      2018-03-26 08:44:54 +0000
@@ -240,7 +240,8 @@
 }

 void MAUSGeant4Manager::SetVolumeInformation(MiceModule& module, G4LogicalVolume* base) {
-
+  G4UserLimits* limits = new G4UserLimits(_stepMax, _trackMax, _timeMax, _keThreshold);
+  base->SetUserLimits(limits);
   // G4VPhysicalVolume* world = _parser.GetWorldVolume();
   G4int nDaughters = base->GetNoDaughters();
   for ( int i = 0; i < nDaughters; i++ ) {
@@ -255,15 +256,8 @@
       // Set auxiliary information
       SetAuxInformation(module, myvol, auxlist);
     }
-    //          else {
-    //          _detector->GetUserLimits().push_back(new G4UserLimits(_stepMax, _trackMax,
-    //          _timeMax, _keThreshold));
-    //          myvol->SetUserLimits(_detector->GetUserLimits().back());
-    //          }
-    if ( myvol->GetNoDaughters() > 0 ) {
-      // Consider adding information to the daughter volumes
-      SetVolumeInformation(module, myvol);
-    }
+    // Consider adding information to the daughter volumes
+    SetVolumeInformation(module, myvol);
   }
 }