Hmmm, that’s how I learned about sex…
Trying to approach this scientifically, the only COW fireforming I’ve done was .22-250 brass to .250 Savage AI, mistakenly using a powder charge of Unique which MD used to make 6.5 Creedmoor cases from .22-250 brass.
Coincidentally, the case capacity of a .22-250 is almost identical to a .30-30 case, right about 43-45 grains of water according to three on-line sources.
I used 18 grains of Unique in my .22-250 cases which John informed me was probably 1-2 grains too much, so based on case capacity alone the load for the .30-30 cases should be around 16 grains. However, with the .22-250 you need to push the shoulders hard against the chamber to form them, I just need to blow them out straight, so probably don’t need as much pressure, so that would indicate a drop of another 2-3 grains. However, the prior experience was going from a .22 caliber bottle neck to a .25 caliber neck, whereas here I’m starting with a .30 caliber hole in a sloping case and going to a .375 caliber hole, which should generate less pressure which indicates a couple more grains of powder to raise the pressure back up, countering the earlier decrease.
Running the numbers through my Fantastic Fudge Factor Findabulator (pat. pending), 18-2-3+2 would indicate a load of 15 grains of Unique as a good place to be. Since the Findabulator is still in beta testing I’ll lower that to 13 grains and see what happens. If the case mouth comes out wide enough to get a .375 expander plug into then I’ll grease’em up good and let the expander do the rest of the work. Otherwise I'll add another grain and repeat as needed.
