I;m not sure where you get the idea that reduced loads are "only" used with faster powders when this is absolutely not correct. Many loading manuals have reduced loads of medium and slow powders to make reduced recoil, etc. loads.
As for detonation, this (elusive) phenomenon is most closely associated with GALLERY loads (small charges of fast burning pistol powders) in which the internal case (may) result in a flash-over detonation etc. As was alluded to above, NOBODY has been able to reproduce this. What is a ALSO wrong with Gallery loads, especially with fillers/wadding is BARREL "RINGING." Not that I don't occasionally use poly-wadding loads in straight walled rifle cases (45-70/38-55), but I know what the risks are.
4895 and Varget are both DANDY options for reduced loads but make sure you don't stray below manual limits. Likewise, I am a BIG fan of BOTH Trail Boss and Red Dot for rifle loads with JACKETED or LEAD bullets in bottleneck and straight-walled cases..