So, having fired many thousands of cast bullet and reduced jacketed loads a few points need to be made.
1. What people call a 'SEE' can come from several things. Keep in mind it is a controversial topic since the mfgs and reloaders with pressure measurement instruments have not been able to duplicate many of the claimed incidents. They usually come from a low load density, a faster burning powder, near max level. I have actually had this happen to me with a Colt 45 and Blue Dot at near max load (the gun was not damaged, nor was anyone hurt). The situation is one where you can create air space between the primer and powder, which makes more of the powder burn instead of a 'gradual' combustion. It is NOT a detonation. It can be destructive but most times it is not. Many cases could be traced back to possible double loads vs a 'SEE'. I have also had a couple of those
2. Some powders (mainly ball) do not like to be downloaded. They do not become dangerous, they just don't provide consistent results. Hodgdon used to have a bulletin out on this topic concerning H110.
3. Lower density loads can be position sensitive, especially below 60%. The problem is the powder can move forward and expose the flash hole (re #1). I have had a lot of experience with this condition and it will play havoc with your ES/SD. Some will load a filler (small tuft of dacron) to hold the powder against the primer (NOT COW or other shotgun/BP filler!).
4. Reduced loads can be useful. MOA level accuracy is fairly easy given the right powder and load density. I had fairly consistent MOA loads with my .308 using cast loads. Powders included IMR4198, 3031, 4064, Varget, and several others. Notice I used all stick powders as they seemed to perform better in this situation.
5. Lyman has a bunch of reduced loads listed for cast bullets. Those loads will, in most cases, work for jacketed as well. Several folks have measure pressure and velocities of cast vs jacketed bullets. Sometimes the cast load is higher pressure, sometimes the jacketed is. Same with velocity variation. Hodgdon also lists some reduced loads, mainly with H4895.
6. The most dangerous part of reduced loads is not having enough pressure to get the bullet all the way out of the barrel. Some of the reduced loads have very little recoil so it is easy to miss. Obviously a bullet in the barrel when a second shot is fired is a recipe for disaster. On really light loads I would pull the bolt and look through the bore if I didn't see a bullet impact on target.
7. If you want to stay in the realm of manufacturer approved loads then please do stay above the minimums listed in the reloading manuals.