Arthur
The first variant of the 100 had a different shaped section to the rear of the pistol under the rear sight. On later models of the 100 this was re shaped and they fitted the web of the hand guard. Mu model 100s serial nr 405xxx do not have the 'third' piece of wood and serial nr 415xxx does. The 2nd variant also has the diffuser at the end of the barrel. All model 102 and 103 have the later build and have the timber web hand guard fitted from the factory.