Holland and perhaps other makers of rifled choke guns had or may have had particular loads for their guns at the request of a client. Westley I think could be an exception as they were trying to sell a gun/ammo system. Here is a Wembely note on one late Holland paradox 40gr cordite and 2 gr gun with Westley capped bullets and 2 3/4" cases.

I didn't remember the Nowatny as having scope mounts. Also all the Super Magnums I have seen have 7 groove paradox rifling.