John;
I do have a W&C Scott & Son 12ga pinfire. By my above method this one would have a throw of about 2.0" (50.8mm) or just above the median of 49mm you stated for the range you have seen. This was just by a rough scaling, not real precise, but I would be about 99.99% certain that is the way it would be measured. Hope this will help your friend to find an appropriate hammer for the Hollis. I have an I Hollis percussion which has one ill matched hammer, but it does have proper throw to work. It is mostly in retirement now but used to hunt it quite a bit.
