I repair a good number of skeet o/u's. To fix a cracked stock I normally dig out 1/8 inch of wood behind the lug that gets the thru bolt and use paste epoxy to bed it. Depending on the break I will remove and replace wood, break off the section and color epoxy to glue it on. I have one Kolar that was in three pieces that is going strong after five years, had one that failed after four years. Side by sides are tougher, I try to remove wood (below the finish) in any area's that absorb recoil and get epoxy in the wood. Splits need cleaned, pried open , coated, and clamped. bill