Michael, from the Mossberg site, the 20ga weighs in at 4.95lb while the 12ga version is listed as 5.25lb, so just under 1/3lb difference. I do not know what video you're referring to but the main visible difference between the two are the different barrel and magazine tube thicknesses and the gap between the barrel and magazine tube with the 20ga version having noticeably more empty space.

the weight of the 12 is %.25 lbs and the 20 ga weighs 4.95. I don't know what video you are asking about but I would look at the 12 ga because of the ability to use the Aguila Mini slugs and buckshot for reduced recoil and increased capacity Slugs budsgunshop.com/catalog/product_info.php/products_id/2446/aguila+1c128974+12+ga+ms+slug+20%2f25 Buckshot budsgunshop.com/catalog/product_info.php/products_id/713073270/aguila+ammo+mini-shell+12ga

Michael, the 20 gauge is 4.9lbs and the 12 gauge is 5.25lbs so the difference is .325lbs. Both have 14" Heavy Walled Barrels with the 12 gauge larger diameter barrel being heavier than the 20 gauge barrel.