I think with ANY of the Old english calibres, you slug the bore before shooting it, EPECIALLY on the 240 Apex, 244H&H, 275 etc (and certain others which are also known to have wide variations).

We had some .243 bullets plated to bring them up to size for the 240.

"You could always try asking Holland & Holland! "

I like that, considering they came out to Australia many years ago to find many of their guns being shot very accurately - to their amazement !!!

I think you'd find more current knowledge in Australia, NZ and the US than the UK, especially to do with reloading.