Looks like a broken off drill bit in the bottom hole.
Maybe someone else had the thought to drill the stuff out and save the stock.
Lead is tough to drill out to any great depth by just going at it full speed ahead w/a regular hardware store drill bit and a Black&Decker.
The stuff grabs and loads up the bit quickly and the drill snapping off down in the lead is a real problem.
Lead shot even if a corroded mass drills out OK as it breaks apart as you'r working on it.
But a solid pour like this appears to be is a tough plug to remove that way.
The broken off drill bit in the lower hole is going to prevent another drill or a mill bit from doing any lead removal in that one.
That deep drill attempt may have helped that lower plug split the wood out.
Not knowing how deep the holes are, and fearing the worst as many home mechanics like to keep going to get the most enjoyment from their efforts, I'd probably start with the stock set up in the mill and w/end mills, start removing the wood around the plugs.
Going deep enough and just wide enough around the set of 3 to allow them to be finally snapped off in there as they will be supported each on a small pedestal of end grain.
What you are left with is a hollowed out butt stock not unlike many done that way on purpose for weight reduction.
But before you plug it back up again, if you in fact decide that you want to do that,,use the now shell of the stock as it is and do the repair(s) to the cracks.
The wood is thinner and more flexible a this point and can be moved around and more easily allaigned and clamped.
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Just the way I'd do it most likely.
Keep the lead and make .490 RB with it.
