There have been three PC M681's produced, all for different distributors. All of these have been 7 shot guns.
The first was for Lew Horton. These guns had a 3 inch barrel with quad porting, as well as having the firing pin on the hammer. There were ~300 units made for Lew Horton.
Pic of Lew Horton version:
The next version to come along was the one for Camfour Distributing. These were made in both 3" and 4" barrels, and were also quad ported. These guns were a later engineering change, the firing pin was moved to the frame mounted style. The front sight was a dovetail version and the porting was changed to a milled flat spot that directed the gas upwards.
Pic and brochure of the Camfour model:
The last version was made for RSR and - again - had some different features. This version had a three inch
non-ported barrel and unfluted cylinder. Also, it had a two toned Birdsong finish. The frame and barrel were green in color while the cylinder was black. Different look for sure. The barrel was similar in shape to the Camfour model, but there were no ports.
Hope I've not forgot anything, going from memory. There may be additional differences and models, but this is all I can remember.
