A factory rifle stock
30 min. epoxy
1/8" x 6" drill bit
'Japanese' thin kerf saw
4 ea. 1/4" diameter x 1/4" long neodymium magnets (I have bought from http://appliedmagnets.com)
Joiner rod material: ideas: 1/4" + diameter piano wire and matching brass tubing from a hobby store, or two pieces of aluminum tubing that fit inside each other or 1/4" + bolt with the threads and head cut off to create a rod and glass bed the holes instead of using tubing
Drill a 1/8" hole from the front of the pistol grip into the buttstock. Cut the buttstock off (use one of those super thin 'Jap saw' or Japanese Saw for thin kerf loss). Cut a steel/aluminum rod (perhaps using piano wire from the hobby store). Sand 1/2 the joiner rod so the glue will stick, wax the other have so glue won't stick. Glue with 30 min. epoxy: rod in the buttstock, and housing in the pistol grip (or bedded hole around rod). Assemble with the pistol grip so they are aligned. Use wax paper between the two parts. Let cure.
Now the buttstock slides on and off the pistol grip. Drill two shallow holes in each piece on either side of the rod, facing each other. Glue neodymium magnets in place with 30 min. epoxy in both pockets, stick magnets in all four holes with proper pole orientation, wax paper in between parts, assemble butt stock on rods to pistol grip, let cure, separate.
Neodymiums are very strong. Pulling apart is difficult. To separate the buttstock from the pistol grip, rotate the buttstock before sliding apart.