That is a very alarming question!
You can ask the local licensing dept to check, however if it is a registered S1 firearm you are in trouble!
If the seller (who may or may not have an RFD) have sold you a S1 firearm then the offence for them in selling a firearm to someone without authority to posses may land someone in prison!
If the gun was part of an estate then I suspect licensing would have been notified of the death of the certificate holder and it would have been placed with the correct authorised holder.
It would be very unlikely that it is a S1 I suspect, a safer option is to take it to a shop that has a chrono and explain asking them to check it! no gun is worth breaking the law for at any cost, they could at least hold it for you legally.