I've been thinking about this brass shim idea, which obviously serves to hold the end of the top tang off of contact with the end grain of the wood stock. What I can't resolve in my mind is the fact that by doing this the sides of the tangs are removed from contact with the stock, as they are tapered and obviously no longer fit snuggly into their tapered mortises. That can't help but to create a 'wiggle' situation of its own which can lead to tang cracks due to lateral deflection- unintended sideways force application. With a shim in place, the only point of contact is the butt end of the lower tang which means stock screw tension is the only thing preventing the stock from wiggling on the tangs, and who would want to torque the bejapers out of that screw? Drawing the screw tight at that point will put undue compression on that lower tang contact point, possibly leading to cracks appearing in the lower wrist instead of the top one. I submit that this may not be the panacea it appears to be on the surface.
Obviously all of this hinges on whether or not the stock is properly inletted or not. I daresay if the stock is properly/perfectly inletted in the first place no shims or other magic tricks are needed (given good wood with proper grain flow through the wrist, and proper screw tension too).
