Wow, its been a while since I have loaded any rounds. My son and I are working up some brass for his new Savage 6.5-284, we started fireforming some rounds @ 41gns. and one by one worked up to 46grns., thats when I noticed black powdery like stuff on the case, like powder blow by, so on further inspection I noticed that the case didn't form (blow out) out like the other cases, it even was lose in the neck die. Could it be the 20 deg. weather, the round in ?? was fired last and was out in the cold for a 1/2 hour. Thanks.

What powder and bullet are you using? If for example you are using a 120 grain bullet and pushing it with 46gr. ACC3100 the result you are seeing is about the size of it. roger

46 gr. H4350, 142 Matchking, Lupua brass with .014 neck thickness, set with .003 bullet grip. I'm aiso using Wilson neck and bullet seat dies.

Sounds like you need to adjust the powder some.
Usually blackened cases mean the charge is a little low.

or you have work harden the brass and need to anneil the necks in order for them to form.