Couldn't even count the #'s of H414 I've burned over the years. Tried reduced loads with cast bullets in a 30-06 decades ago and ended up with hang fires when it got cold out/winter in ne ohio. Needless to say no more reducing loads more than 10%
Back in 79/80? again in ne ohio winter time. A buddy (ya a I know a guy story) and my brother were shooting/testing 357 mag loads. Jerry was using a model 27. Somehow he managed to split the cylinder in 2 pieces (broke in 1/2) using bluedot and 125gr jacketed bullets. They went back to my brothers house and gave me a call. We pulled the rest of the bullets checking the powder charges weights. They were all spot on to the +/- 1/10th gr. Jerry swore up and down he didn't do a double charge & we tended to believe him seeing how a double charge wouldn't fit into a 357mag case. Try putting 28gr of bluedot in a 357mag case and you'll see what I mean.
I understand pre-detonation, never saw it and don't ever want to experience it. I'm not going to say I have a better chance then the next guy to find out 1st hand what pre-detonation does. But I do shoot +/- 2000 cast rifle bullets a year with reduced loads (way more than the 10%/starting loads) doing ladder tests with different 30cal cast bullets. A new mold/new to me mold ='s testing with +/- 10 different rifle powders.
per-detonation ='s ok ya if you say so, powder companies know more than me
squibs ='s absolutely, not good
I'm impressed that know one has brought up flame cutting. Molten junk in the bbl is never a good thing. But the face of the bbl & forcing cone is what takes the beating. Light/low end loads of AA#9, 2400, H110, WW296,MP-300 and you start sandblasting your bbl. Low pressure loads with these types of powders ='s incomplete burn and the end result is bbl faces that look like this.
That's actually normal wear and tear on a used hard/put away S&W 586 bbl after +/- 75,000 rounds. I pretty much do all my testing with low pressure loads using magnum powders for the 357's in dw revolvers. It's easy enough to toss the bbl in a lathe and clean up (new, shinny) face of a bbl before testing looking for flame cutting after a range session.
The worst flame cutting I've ever seen was when I ran a 4 boxes (200 rounds) thru a dw 15-2 using cast bullets with a plain based gas check. The plain based gas checks were made out of soda cans. The bullet was the H&G #51 and the powder was full house loads of power pistol. Power pistol burns hot and the only thing I can think of was the powder burned hot enough along with the cans coating igniting to melt the thing +/- 3/1000th's aluminum can. I should took a picture of the destroyed bbl. It had flame cutting like the bbl pictured above the whole way around the face of the bbl that ate into the forcing cone. I had to cut that bbl 1/4" back and re-cut the forcing cone to get rid of the flame cutting damage. This was back in 2014 which led me to start powder coating bullets. Was trying to find a way to drive soft (8/9bhn) cast bullets hard and still maintain accuracy.
Anyway if you want mid lever, low end high level magnum loads you'd be better off using powders suited for that purpose.