If it is an 8mm then send it back. Demand a refund.
Same thing happened to me last year with what was supposed to be a muzzle loading 10bore with a shiny bore which turned out to be a 15 bore with a sewer pipe for a barrel!
The auctioneer wasn't happy but the fact was quite clear that the description wasn't even close to the actual item.
-------------------- He who lives in the past is doomed to enjoy it.