Major ,Sir Gerald Burrard,covers the issue of," cracked actions"in his book;The Modern Shotgun.Vol,The Gun,1 pages 73-82.Vol;3,The Gun and Cartridge,pages,401-403.Burrard compares the physical strength and properties of various side lock and boxlock actions.
He recommends boxlock guns be fitted with a top rib extension with a reliable 3rd,fastener in order to minimise the risk of action cracks!
Burrard illustrates the adverse effects of over-heating of the action on the physical properties of the action metal.Ilustrated is the microstructure before and after excessive heating and the cracked action that resulted from over heating!
Burrard also stresses the need for adequate metal thickness of the water table and the need for a corner radius at the junction of the water table and the breech face so as to avoid stress concentration so as to minimise the risk of action cracks.
He expresses minimal concern over pin holes drilled on or near the neutral axis of shotgun actions as they are unlikely to act as stress raisers.
Burrards work on the analysis of shotgun design is still the most comprehensive design review available and is recommended reading.
