The Federal catch to your "split a case" is, the powder must be paid for by each member that is going to get some powder before the order for the powder is placed.
Then each member that has already paid for his/her powder may receive it from whoever sent in the money to pay for the shipment.
Legally, the person who orders the powder is acting as an agent for the others. He is not buying the powder for the club, or for himself.
If the person just buys black powder in the name of the club and then turns around and sells it to whoever wants to buy some, he is breaking a Federal law unless he already has a license to sell black powder.
If he/she doesn't do the "agent" thing you would be doing him/her a big favor by informing about this.
It could keep him/her out of a Federal prison.