Potential patch attached. Nb: I note that most of the tests in test_mappybeamlinesimulation are failing right now. I put in a mockup CallG4bl thing which one could extend to make them pass... but did not dig too hard (too much else to dig into right now).

Another issue - the json cpp -> ROOT/C++ conversion can't handle more than 32 bit integers. It is possible to fix without too much hassle. For now I only permit 32bit random seeds (note this is 2 billion random seeds allowed, which means non-zero probability of a random seed collision).

So it looks like the latest version works - attached integration test in test_simulation_beam.tar.gz (along with unit tests in the random_seed.patch_2 which was a hack of stuff in duplicate_primaries.tar.gz).

Hi Chris, I remember seeing similar duplicate primaries in my G4beamline input deck. This was when I was using MAUS v0.9.7; if I recall correctly, the issue was resolved when I switched to v1.4.0, which was the latest version at the time. I have also ran a recent simulation with v2.4.0 and according to the attached primary.log file (from your primary.py script), the duplicate primaries seem to be no longer present.