The "frame size" thread from the old site has been deleted. However, I copied it a couple of weeks ago. I will make any information in it available to the builders. It seems the most common size of XX frame is the one inch pin separation. It is also the smallest pin separation of the known variations in the XX frame. There is no reason to make the separation any smaller in the interests of a lighter gun since it would make it not compatible with original guns. It (the one inch) is the one that should be used since there is some possibility that the new barrels may be fitted to existing XX frame guns, an intriguing possibility, and a chance for the builders to make a little extra money (selling barrel sets). If a customer is interested in making a 28 gauge gun as small and light as possible, he can profile a standard XX frame and reduce the size of the breech balls to suit his own wishes.