Reduced loads are bloody dangerous.
If Hogdons lists a 60% load for H4895 then this is neat, good information to have, BUT! ...........just arbitrarily dropping low charges, especially low charges of slow burning powders like 4831, H1000, RL22 etc is asking for trouble. Maybe this H4895 info will give pfranklin something to work with.
The mechanism of blowups from reduced charges is poorly understood with terms like "detonation" and "powder plugging the neck" and "complete involvement of the powder charge" being thrown about in an attempt at explaining the phenomenon. BUT IT DOES HAPPEN! This is incontestable.
Changing the "burn rate" of your propellant will result in some weirdnesses, as papapaul lists earlier he has 81gr go overpressure in cold weather.... "detonation???" I don't rightly know. IMO if it WAS a detonation it involved only a very small remaining portion of the charge. In my limited experience detonating smokeless powder causes it to unload energy like dynamite but it takes a really fast hit to detonate it, something on the order of 20,000 ft/sec. Using the wrong powder, a "fast" burning powder when a "slow" powder is called for can cause blowups from overpressure WITHOUT detonation...... powder mixups which result in extremely rapid deflagration will take rifle actions apart. I can think of several examples...... a well known benchrester was killed by a mixup of pistol powder in a PPC. The energy is there and available and it needs to be correctly channeled. If it isn't the result can be catastrophic.
I dislike large cases and slow powders for this reason. I've never been present during a blowup but have seen my share of UNDER-pressure events which oddly enough can be the precursor to an OVER-pressure event. I consider myself lucky. I try to learn from my luck!
I'm an experimental type, I'd feel safe exploring the 60% H4895 loads........ but I'll never attempt to come up with my own reduced loads using another unlisted powder and a big case.
Life's too short, then you die.
BTW Lynn, how do you use Tyvek? IME it's like tough fabric, how do you use it as filler?
al