While you are on the site, in your browser find and click "Add to Home Screen" A CGN beaver app icon will then be created to your phone that is directly link to the site.
Note: This feature may not be available in some browsers.
The barrel is tapered with the larger diameter at the rear sight and smaller diameter at the muzzle, so it depends on where the bipod is mounted to. There is adjustment allowance on the ones I've seen.
If you don't have a vernier caliper you can use a piece of string to determine the barrel diameter. Circumference = pi*diameter so diameter = circumference/pi.