I normally use KAPOK for a filler, using enough to make a good snug loading. Lately, in other cases, I have experimented with GREX and other shot buffers, without detrimental effects. Tests continue looking for melted plastic in the bore, but so far, show nothing amiss.
: When testing, I load knowing how many grs. are being used, and use that for making a volume measure to throw that amount of powder, thus finally changing to a stricken measure. It still throws X number of grains, even though it is a volume measure. Weighing BP to exact # of grains for each ctg., seems to be a waste of time - on the chronograph and target alike.
: It has been a long time since I have done much shooting with a .577/450.
: I-too have switched from dacron to kapok.
: I assume when you say "don't load by volume", you are saying don't fill the case, as you would with many straight cases. Mine seemed not to mind, no matter which case was being used.