Our initial data suggests the stone inclusions give a mass reduction compared to solid lead of 18–41%, while iron gives a reduction of 12–27%. The degree of reduction depends on the volume and type of inclusion. While the specific gravity of lead is 11.35, that of wrought iron is c. 7.6–7.91 and cast iron c. 7.21. Stone has an even lower specific gravity but this varies significantly depending upon the type, the highest being basalt at c. 3.0, while limestone is c. 2.61–2.85 and flint c. 2.4–2.6.

Given the large size of the Mary Rose assemblage (267 composite rounds) and the fact that none had been fired, the Mary Rose Trust considered it acceptable to sacrifice several rounds to destructive analysis to explore their composition.¹¹⁵ Cutting the rounds in half in this way is not a practical option for battlefield round shot, because currently they are so rare and each preserves a unique combination of firing and impact evidence. In addition, when dealing with irregular and especially multiple inclusions, especially if in the form of stone fragments scattered through the lead, simply cutting the shot in half is not adequate. What was required was a non-destructive method which would yield 3D data in high definition to reveal the whole composition of each round. Radiography had been attempted on the Mary Rose assemblage but, as lead is largely opaque to x-rays, even on the smaller calibre rounds the results were poor.¹¹⁶ An alternative technique uses neutrons, which are able to penetrate heavy metals such as lead.¹¹⁷ Neutrons are elementary components of matter, with all atomic nuclei except for hydrogen being made up of protons and neutrons. Neutrons can be used as free particles in the form of a focused beam to carry out a range of scientific experiments such as neutron diffraction, to study the atomic structure of materials; neutron scattering, to study the dynamics of materials; or neutron imaging. The latter can be applied either to produce two-dimensional images or for neutron tomography which is three-dimensional.