Steve,

There is a chapter on the 20 bore paradox. There are chapters on all the bore sizes made. Only 25 20 bores were made. The book only provides 22 based on action types (4 hammers and 18 hammerless). I don't know the technical information you are trying to find out. The short chapter has information on weight, action type, top straps (listed as all are short), all barrels 28", ejectors (most had them), sight leave ranges, cartridge loads, etc.

Ken