Bearing Surface Diameter
Definition
The diameter of the projectile face in contact with the bone surface at the moment of impact; smaller than the resulting defect diameter due to tensile failure enlargement; the outer-table defect approximates the projectile diameter but is unreliable for calibre estimation.
- Defines
- Projectile face diameter at moment of bone impact
- Relation to defect
- Smaller than the resulting entrance defect
- Cause of enlargement
- Tensile failure of bone beyond contact point
- Calibre estimation
- Outer-table defect is an unreliable calibre proxy
Common questions
Why does the entrance defect not directly indicate bullet calibre?+
Bone fails in tension around the point of contact, so the visible defect at the outer table expands beyond the true bearing surface of the bullet. Using the defect diameter alone to back-calculate calibre overstates the true projectile size.
Why is the outer-table defect an unreliable calibre proxy on its own?+
The outer-table defect is the closer physical analogue to the bullet's bearing surface, but its size still shifts with impact angle, bone thickness, and secondary fragmentation around the entrance. Recovered bullet fragments, the wound track through soft tissue, and radiographic imaging of retained fragments give firmer calibre evidence than bone defect measurement alone.
Related terms
- Contact Wound
- A firearm wound produced when the muzzle is pressed against or within a few centimetres of the target surface. Characterised by a...
- External Beveling
- The cone-shaped defect geometry at an exit gunshot wound in bone: the inner table diameter (entry face of the defect) is smaller...
- GSR (Gunshot Residue)
- Primer-combustion products (classically lead-barium-antimony compounds, now also non-lead formulations) deposited on the bone surface at close or contact range; detected by SEM-EDX...
- Internal Beveling
- The cone-shaped defect geometry at an entrance gunshot wound in bone: the outer table diameter (entry face) is smaller than the inner...
- Keyhole Defect
- An asymmetric gunshot defect produced by a projectile striking bone at a shallow angle; one end shows a conventional beveled entry geometry...
- Puppe's Rule
- The 1994 formalisation of the principle that radial fractures from a subsequent gunshot terminate at fracture lines already produced by a prior...
- Secondary Projectile
- A bone fragment or other material driven at high velocity through adjacent tissue by the primary projectile's passage through bone; produces irregular,...
- Stellate Fracture
- A set of radial cracks extending outward from the main gunshot defect, produced by compressed propellant gas pressure radiating under the scalp...
- Trajectory Reconstruction
- The forensic procedure that integrates the osteological bevel direction, angle-of-impact estimate, and the physical scene evidence to reconstruct the relative positions of...