Glad you clarified that!
As a long time Unique user and reduced velo cast bullet shooter I have had to deal with the issue of using or not using fillers with a variety of powders and the velocity effects, verified on my Chrony, of various powder positions within a voluminous case. I concur with C. Dell and W. Schwartz (The Modern Schuetzen Rifle) that the most consistent ignition and velocity will be achieved with the powder back at the ignition base, though it does not have to be held there by a wad or filler. In fact, improper use of wads has 'rung' many a chamber; I will not use them anymore. Chambering a round, elevating the muzzle (finger OFF the trigger, please) and lowering the gun into firing position will achieve this powder position. Admittedly, it is not inconvenient when shooting offhand, moreso off the bench.
The 45-70 Trail Boss 70% of capacity starting load is so mild that kids, and those 'timid' of guns should not object. Full case loads of it are lighter than a 405/65gr charge of black powder in my 'trapdoor'. Absolutely no powder position issues, dbl. charge or airspace issues, clean burning...whats not to like?
I can understand having a bunch of fast powder, thus 'cheap' per powder charge and many per can, but it really isnt the best choice, maybe not even a very good one, with the options we have today. 'Frugal' as I am, I happily bought the 5# jug of TB after feeling it out in my calibers. The old Unique and RedDot jugs are going to get considerably less use.
