Before any crack repair, I would first investigate/correct the reason why the buttstock forward ears (the "recoil lug" area if you will) didn't support the action/tang enough to keep it from driving into the rear of the inletting, cracking the stock there.
On most rifles, there's usually some wood/metal clearance at the rear of any tang, usually unseen from outside the stock, to preclude the rear of the tang inletting acting as a defacto recoil lug area.
If the cause isn't not found/corrected, there's a pretty good chance the crack will only redevelop again/further.
I repair small cracks by drilling along their length, from inside the inletting, one or more small holes at slightly different angles to make a criss-cross pattern of holes/passageways within the stock at the crack, but below the surface, then mixing some sawdust/drilldust from the subject stock with epoxy, and force the mixture down the crack/holes with a toothpick/etc.
I then clamp the crack back together, until dry.
BTW - when working with any glue/epoxy, it's a good idea to first apply paste wax to the stock's outer surface, so cleanup of squeeze out is EZ.
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