As an alternative to the GoPro Sportsman Mount, Choate Machine & Tool has made their own GoPro mount. It is machined aluminum. It uses a simple steel barrel mount to attach the GoPro mount to a barrel or magazine tube.
You do need to use a factory GoPro screw and capped nut off of a GoPro mount.
As you can see, this mount is set up for shotguns. Whereas the GoPro Sportsman Mount seems to be more versatile and can clamp onto other firearms as well as bows. I have picatinny mounts for my firearms with rails but my Mossberg JM Pro 930 does not have any rails to mount my GoPro. The Choate GoPro mount cost me a lot less than the Sportsman mount and is made of metal.
I purchased this at the FNH USA 3gun match at a discount but have not been able to find it on Choate Machine & Tool’s website. I have inquired about the availability online and the retail price. I will update you as soon as I find out.
UPDATE: After Talking to Fred at Choate, the GoPro shotgun mount is up on their website. It retails for $42. There are no pictures of it on the site as of yet, but it will be updated soon.