Red, If your rifle is a original H&H (or built to there specs) it has a .245" groove diameter.
Here in the States I have heard of a few in use, with Sterling Davenport building a "new" one with a .245" barrel, as the owner had a vast supply of bullets and ammo.

All custom ones I know of use the common .243" groove barrel from various makers. Ross Seyfried probably was the last to do a article on it quite sometime back. He used a .243 barrel and got some rather exciting velocities with the 85gr Barnes. I have/had some info from Colin McKelvie on a rifle he used as well, again some astonding velocities.

To me it (as well as my favorite .240wby) it seemed to be a rifle for a 100gr bullet. That said I really like the 95gr Berger, but close enough.
As for data in the .244 H&H, through my use and a few friends, starting loads where;
72gr H1000
75gr H5010
65gr 7828ssc
65gr RL25
70gr VV570
with 100gr bullets in WW .300 H&H cases and cci-250 primers.