Job 1 would be to determine why or how the crack happened. Makes zero sense to repair a crack if it's just going to happen again. Was the crack caused by abuse (dropped, stepped on, during an attempted bend, etc)? Was the crack caused by neglect (loose or broken hand pin, breech pin, trigger tang screws, oil soaked, etc).
Depending on the severity of the crack and it's location, gluing should work in a non-critical location or if the crack is small and non-continuous in nature. Epoxy might be in order if the crack is more severe. The next option would inletting dowels, staples or pins...this option would the more expensive of the repairs but also the most definitive.
Hope this helps.
