If it is, or anything like this one

https://www.gunsinternational.com/guns-f...un_id=100649951

You have a very lovely Rifle.

Boddington in Safari Rifles does I think mention the 275 H&H Magnum as one of the several but now obsolete 7mm Cartridges - nothing wrong with them, but just never caught on. Not sure if the 275 H&H Magnum was ever released to the "Trade" unlike the 300 and 375 H&H, so the number of rifles built would have been but a handful, and hence appearing in literature even less so. Most would have been in 275 Rigby, if European, then 7x64 and of course the 7mm Remington Magnum has been very popular.