Thanks for the input Gentlemen. I agree, about 1:14 would be my guess as it is similar to the 9.3x62 with a similar bullet weight. Could be 1:12 like the 375 H&H but as the Rigby was earlier when they tended to use a slower twist rate I recon 1:14 is more likely.

Underlever, thanks for going to the trouble, I am looking forward to your answer. By the way, your rifle sounds like a beauty.

Matt.