I finally decided what to do and used waterproof PVA to make the repair.

As I tried to open the crack around the grip some of the PVA was put into the split. I used a small syringe, but as much would have been wiped into the joint with the index finger as went in from the syringe as the gap would not open wide enough to get a good amount of glue into the joint.

The stock was left clamped overnight (even though it says the bond is made in 5 - 10 minutes) and this morning the clamp has been removed.

I think only a tiny amount of PVA was actually taken into the hairline crack as I could not open it up very much, so I am hoping it was enough, although I am sure not enough PVA went into the joint to reach the dowel inside.

There is no more "movement" in the stock, so I will wait another 24 hours before shooting the rifle and see if this small repair has worked - if not I will wait for it to get worse so I have more space to inject more adhesive next time amd maybe accept that I need to fit a new dowel.

If the stock should ever break open, I actually think the repair would be easier to make.

It is surprising how much movement could be felt in the stock before the repair was made, so tomorrow I will find out how good the joint has been bonded and if it remains solid.