I have the 0000 frame pin separation dimensions in my notes somewhere, but don't have them handy. No, the separation is not in progression with the other frame sizes. If I remember correctly, it may be the same separation as the 000 frame. By the way, a set of 16 gauge #1 frame Parker barrels fits nicely on a 1/2 frame gun. I happen to own a gun set up that way. You have to have a zero or 1/2 frame forend to make it work. Will we see you at the Northeast Shoot in June?