Its almost a forgotten arcane art but was a lot more popular in the mid 20th century. A range of good pistol powders were now on the market and people having less money took advantage of economical loads for small game, teaching shooting or plinking. You say 'reduced load' to most hunters( particularly aussies who are high powered bolt actions owners) they think you mean dropping from AR2209 back to AR2207.
What I am talking about is when a lot of old load manuals had a section devoted to running small loads of pistol powders in large rifle cartridges. Much like trailboss does however most people dont realise a bunch of pistol powders can work like trailboss in a rifle cartridge. ADI still lists a couple loads with a few grains of AS-30N in 308 and 223 to get speed of sound loads with jacketed bullets.
There was also a famous load called the guard load around WW2, a few grains of bullseye in 30-06 cartridges and jacketed bullets used for POW/military prison guards where you didnt want a bullet going through an inmate into the nearby town. it acheived speed of sound levels with the regular military jacketed bullets, decent accuracy too apparently within its range.
Also a bunch of loads dedicated to magnum pistol powders like Alliant 2400 which in 15-25 grain loadings will get a variety of full size rifle cartridges safely to sub 2000fps level.
A lot of this art is forgotten outside of cast bullet or other enthusiasts. As mentioned with the luxurious late 20th century lifestyle why bother with this when you can plink with full powered packet ammo.
I always said this art would return if the worlds economy tanked but what I didnt predict was pistol powders themselves becoming so much harder to find than rifle powders! Now if you are looking for the longest term term option you are better off filling the gunsafe with something that uses Ar2208