Here is what I did to a pump gun stock head that the top one third had cracked off.
Sounds like your's only needs the head repair seeing it's not come off. You can also spread the crack a little and wick in super glue; Loctite Control formula.
I used 7/16" Stanley staple gun staples vertically across the crack. Drilled holes for the legs, made a channel from hole to hole so the staple would be a little below the surface of the face; filled the holes and channels with acraglass along with a thin layer of acraglass on the stock head face to have a perfect mating of the stock and receiver so it won't happen again;inserted staples; applied release agent to the receiver; installed stock and snug the bolt. After curing, and removing it looked like the pic. You will have to look closely on the left side to see the crack there; right side you can see.
http://www.shotgunworld.com/bbs/cpg1410/displayimage.php?pid=6703&fullsize=1
