I have a long experience of reduced cast bullet loads with a 375H&H by CZ, (With Calfornia stock)I bought used in 1975,And a brief flirt with a face punching 458W CZ with the masochist's German Boar Hump stock.
I have even got two rugers 77 ,one in 416 rigby and one in 458 Lott.
They all shoot well with NO hangfires using Rem magnum primers and Winchester Large Rifle primer,igniting slow shotgun Italian powders,similar to your Unique and the slowest Rex powder,numberIII,the one we call GREEN in Italy.
With different powders i.e. 4227 and ancient RKK 19 I had to use kapok to avoid double bang firing.
These methods are not invented by me,I follow Ed Harris advices,use easily ignited powders ,the previously listed primers and no fillers and tame the big boomers.
I agree with BruceB that it is not a good practice to reduce the charges of progressive full load powders