Thanks to Brad Hedges here is instruction to causation and repair of cracks in fore-end woodwork.
Cause: The crack was caused by the draws at the rear of the fore-end compressing or failing, allowing the fore-end to move forwards and backwards under recoil. Once the draws are stuffed, the next thing to absorb recoil is the front trigger-guard bush. Tightening the main screw does not grip the fore-end to the receiver, rather the bush is there to stop the screw and trigger-guard from crushing the fore-end and messing up the trigger to sear contact, resulting in losing the second pressure on the two stage trigger.
Once the fore-end moves around, the main screw bush acts like a wedge and breaks the fore-end.
Repair: You can open the crack up enough to get the glue of your choice in there. Clamp the crack closed. Drill through from one side to the other and put a length of the threadwire in the drill, slowly and steadily spin it in. This wire threads into both sides, so it won’t pull them together, but will hold them into the position you have clamped. If you screw the rod in just short of the other side you will have only one side to trim once all is set.
All of this work is for nothing if you don’t fix the draws as well.
The main screw bush needs to be floating and able to be adjusted if needed. It is supposed to be .2mm shorter than the wood so it holds firm, but does not crush.