The only Unique loads I use, that don't have powder charges thrown by hand, are those that are done on my progressive press. In that case, my tolerance is +0.2 gr / -0.1 gr. However, the Dillon powder measures drop Unique with such accuracy, that it usually deviates less than 0.1 gr. And, the Unique loads that I run on the Dillon were specifically developed with that tolerance in mind.
As far as "Magnum" loads and Unique, though... I don't mix the two. The burn rate and density of Unique just doesn't get along well with the 'magnum' loads.
I'm a big fan of Unique. I use it in quite a few cartridges and loads. But... Unique in 'magnum' cartridges is like putting a 2.0 Liter supercharged 4 cylinder engine in a semi-tractor. It might put out enough power to get the job done, but it is far from ideal. ...not to mention, Unique is a dirty powder, unless you're running it at near-maximum pressures. In 'magnum' loads, that rarely happens; so it's always dirty.
Most of my "Magnum" loads are in .44 Rem Mag, .32 H&R, and .327 Federal. In those cartridges, H110/W296, H/IMR 4227, 2400, Pro300MP, Lil' Gun, True Blue, and Blue Dot do the dirty work.
Out of my Uniflow powder measure, my general tolerance is +/-0.1 gr. Some loads may have been developed specifically to allow for more deviation; but I'm usually pretty anal about being exact.