Yes would be interesting to date the Kynoch cartridges if the box is with them or Steve still has the original box.
Need both the date code and also if manufactured by ICI (Imperial Chemical Industries) or IMI (Imperial Metal Industries). Kynoch repeated their dating codes and knowing if ICI or IMI can narrow down to which dating period the codes apply. Information on the front of the box such as if loaded with cordite or nitrocellulose also helps identify if earlier or later loaded ammo.

I'm not going to hazard a guess at the velocity other than definitely under 3000fps, I'll wait for the proven results.

Info needed as in example below.