The shape of a sidelock's plate, in the rear, is a wedge. The better it is inletted the more the wedge effect can try to spread the wood apart in the rear. When there isn't a lot of wood contacting the action at the head it compresses easier. As it compresses, the wedge effect of the lock plates begins to force the wood in two opposite directions, eventually resulting in a crack. One thing that contributes to this rearward movement of the action "into" the buttstock is a loosening of the tang screw, or hand pin as the English call them. It is very important to check these and keep them snugged up, regularly.
I have a LCS 16 ga. FW that had been restocked, very expertly, IMO. I traded for it some 12 years ago, and it was crack free. I used it often for doves and crows, and some clays, and eventually cracks began to appear on each side immediately behind the lock plates. I caught it as they were just beginning. Jim Kelly stabilized them and did some "glassing" in the rear of the lock inlets, on each lock inlet. Nothing shows, and I believe it will outlast me now with no more cracking. OTOH, I have a 12 ga. LCS 3E that has original wood, has been shot a lot but taken good care of, and it remains crack free after well over 100 years. And, it was originally owned by a pigeon shooter who likely used stout loads in it.
Though pressure and recoil MAY be correlated, it is recoil that cracks stocks.
That is exactly right.
SRH
