Thank you for submitting your item for appraisal. This appears to be a very rare gun. A comparable Flintlock seven-barrel musket (volley gun) is in the Royal Collection Trust. This volley gun features seven smooth bore barrels, the lockplate stamped "TOWER" with a Crown engraved at tang of lock and and various inspection stamps. The musket in your possession appears to be in very good condition with only small restorations. A comparable musket with excellent provenance and great untouched condition and patina sold for over 30 000 USD at auction ( with a much lower pre-auction estimate) not long ago. The estimate is based on few auction results. There is no measurement for the sentimental value you might attach to the item.