Re: CORN MEAL.......AINT JUST FOR BISCUTS!
Not sure what the .300EX is, but I just formed a batch of brass last weekend with this method. I was making .270 OTTR brass which is a .243WSSM necked up to .277" and the shoulder reformed.
Cases were primed with CCI250, charged with 10gr of Bullseye, half sheet of toilet paper stuffed on top of the powder, then the case is filled with a "Cream of Wheat" type cereal and packed tight to the mid point of the shoulder and topped with another half sheet of TP to the top of the neck. This powder charge in the WSSM cases forms them to about 95-98%.
I use a capped pen to pack the first piece of TP, cereal and last piece of TP.
The makes a loud pop when fired so where eye/ear protection. And it's not a bad idea to patch the bore every 5-7 rounds. The only thing to change for larger/smaller cartridge would be the powder charge. Think I heard someone (BlackDiamond 408 or Fifty) mention that they use around 50gr of a FAST pistol powder in the .408 based rounds.