Actually, that's the distance selling regulations, and they do require the goods returned to be unused and in saleable condition - even though you've said you're not going to mount the scope on a rifle, I'm guessing some would and that (If it causes any marks at all) means a refund could be refused...as could damaged packaging if the goods can't be resold as new.
Any protection under the CCA only applies if you buy via CC, whereas the distance selling regs apply to any mail order transaction.