JMV375:
This query is difficult to answer without more information. Since Kynoch do not list the cartridge amongst their current offerings ( http://www.kynochammunition.co.uk ) I assume you are referring to a pre-60's manufacture box. Since that would be of interest to collectors, expect to pay collector prices. This means that condition of the box, date of manufacture, and condition of the cartridges will heavily influence asking price. Do you want them to shoot or add to your collection? ...or are you offering some for sale?

The best source of current prices for collector-ammo is to browse the auction results. Failing that, dealers like Pete de Croux (sp?) in the US might be worth contacting. Hit the World Wide Web.