Holland & Holland did not have a predominence for their choices regarding Indian buffalo Horn or ebony on forearm tip. Their guns were truly "custom made" for the enquiring gentleman for that period of time as they are today. Barrellength too was a bespoke option.
I am sure H&H advised their customers to some point on what was sencesible, to ensure that the sportsman would be fully satified with his weapon.....and with their name engraved upon it

When said all this though.... of the majority of H&H boltaction and singleguns I have seen with Indian Horn has been small bore guns. Indian Horn seem to crack if too much strain is put on them...but that does not relate to a period of time but rather to nature of caliber...