[sullivan]

Firstly
Commiserations on your v bad luck

To a died-in-the-wool tinkerer like myself, this is almost as much fun as going shooting but do You want to go down that path? To me, it is an absorbing and rewarding hobby where many hours have been spent at my bench in the garage, solving a range of problems.
The cheap way would be to pre-drill a hole or two for a small countersink-head, wood screw between the butt and swivel. Lever up the crack at the butt with, say, a small, sharp screw driver and squirt PVA glue into the gap. You can buy craft glue with a spout, in a squeeze pack. After installing the screw/s, wipe off excess glue with damp rags. Ideally, you would be clamping the butt in a padded vyce that is attached to a stable bench. Right now, you should have an idea of what you are in for where tools are concerned and you have not even started work on the butt plate. IMO, a new one is unlikely to fit flush with your butt and a refinish of the stock will have to be considered in the future. This kind of thing is Fun for me. Therapy, if you like:biggrin:
I forget who it was but someone suggested a new butt. That would look a lot prettier, however it would have to be inletted and finished. Still others have suggested clamping and gluing and that would be a Lot neater. It is easy for me to say because I have long, sliding clamps too. Just something for you to think about mate

Good Luck, whichever way you go:biggrin:

 

[sullivan]

A couple of little "dowels" would work there. Some kind of pressure will have to be applied after assembly of the joint but the large chip will have to be clamped to the butt while the dowel holes are being drilled. That is, the detached piece has to be in situ while the dowel holes are drilled. Once the dowels are in place the joint will not slide apart under clamping pressure.

 

[sullivan]

It just ocurred to me to question whether that detached chip would really slide under clamping pressure. You might not need dowels at all. Those mating surfaces look pretty rough and that could be enough to prevent sliding. Just a thought. If you feel better with dowels. by all means go ahead.

 

[sullivan]

Same thought: could I use a dremel to carve the sliver out of the stock beneath the butt pad? This was suggested earlier but I couldn't figure out how without it becoming a train wreck.

Saw this Q last night. Morning now and no replies. Never had to do this so I am guessing.
1) Describe a circle on the flat surface of the butt that is greater than the width and thickness of the missing piece
2) Drill down around the outside of the circle with say, a 1/8th drill or smaller.
3) Keep the holes as close to each other as possible
4) The depth of the holes should be say, 1/4 inch deeper than the length of the chip
5) With luck and if you join up all the holes, you might be able to break off the island of wood at its bottom by levering with a small screw driver down one or more of the holes.

Never done this myself so good luck. Doing it this way, you will have the grain running in the right direction
6) Make the holes bigger if there is not enough leverage