*grammar*
Don't worry, it's legal. You can have it linked as much as you want, it's just the full auto rifles that are prohibited. The only ammo that's prohibited/illegal is armour piercing rounds, incendiary, flechettes, etc etc, but just because your rounds are linked doesn't make it illegal. You'd most likely be good to still shoot it if it doesn't show any signs of wear. (which is why some of the guys are being so kind and offering to take it off your hands

)
As for finding out what caliber it is, post some picks of one or two rounds next to some household items such as lighter, pack of cigarettes etc and someone will be able to identify it.