Interesting point but would that really be relevant? If you have a hollow pit or one with an initiator in the center, you will be making two half-spheres, so yo

Interesting point but would that really be relevant? If you have a hollow pit or one with an initiator in the center, you will be making two half-spheres, so you will be far away from the critical mass. And even if you are making a solid pit, I would have assumed that you are quite a bit away from the critical mass without neutron reflectors and the compression from the detonation.