Officers are continuing to investigate an aggravated burglary which occurred at around 9.50pm on Wednesday, September 19.
Two men wearing balaclavas broke into the North Yorkshire property.
They stole a 28 bore shotgun made by the Australian company Cowles and Dunn, as well as 12 bore shotgun and a .22 rifle fitted with a silencer.
Other valuable and sentimental items were taken (full list below).
Officers are supporting the homeowner while enquiries continue to track the culprits down and recover items.
They are urging people to come forward who may have been offered similar items for sale since the incident, as well as any suspicious behaviour in the Masham area during the past week.
Anyone with information that could help the investigation is urged to contact North Yorkshire Police on 101, select option one, and speak to the Force Control Room.
Other items stolen included:
A silver christening mugs engraved with floral decoration, Birmingham, 1863
A silver christening pot/mug, Wilson & Gill, Regent Street, London, 1900
Filigree caddy spoon
A rectangular hinged trinket box, Barrett & Sons, Piccadilly, London
A silver heart-shaped pill box, London, 1891
A silver partridge – one of an identical pair
Halcyon Days enamel circular boxes, one decorated with a bee.
Circular tooled snuff box, Birmingham, 1927
A small rectangular Vinaigrette with “LAB” on lid
A silver carriage clock in red leather case, Carrington & Co
A silver chatelaine with six chains including a pin cushion, locket with photo of a child, vinaigrette, scissors /case, spike, thimble in basket, tape measure, larger locket with hair, thermometer case
Silver heart-shaped Victorian Ashtray, Foliage & Birds
An Apple iPhone 5SE
A Landline telephone handset