Case colours are a very pleasing addition to any gun.The prime purpose of case hardening is to provide a hardened wear surface on the action, fore end, lock plates and certain pins and screws.The process is controlled so that the penetration of the hardening is limited to.005 inch approx; at the same time care is taken not to diminish the strength of the core metal.
Unfortunately in the process of recase hardening,increased case depth [carbon penetration]may result and the strength of the action of the gun may be significantly reduced.
Some years ago whilst reviewing restoration of a best English gun with a reputable English gunmaker, the issue of recase hardening was discussed.
The gun maker said they would not undertake the work unless I accepted full responsibility if the gun failed in reproof!
To illustrate their concern, he produced the action of a best London S.L.E. That had failed reproof following recase hardening.The failure occured at the junction of the water table and the vertical breech face, excessive carbon penetration was evident. My gun was hot recase hardened!
Recase hardening is currently in vogue. My question is: What process controls are currently used to avoid the problem described above?[ie:excessive carbon penetration and reduction in ultimate strength of the core metal]
