6mm ai and cream of wheat fireforming

quick run down my friends brand new 243 was having issues after 40 rounds being fired it started not wanting to let bolt close no idea why. all kinds of brass flake inside chamber anyway we had it reamed to 6mm ai shot some handloads that was given to us by the gunsmith that did the reaming, shot it yesterday and it shot 3 3 shot groups from .6 to .4. shes gonna be a winner, anyway im gonna have to load for it, any recomendations on powder and charge. the ones we shot yesterday were viht 590 but that powder is hard to come by.
next question anyone know what powder and what charge i can do the cream of wheat trick for fire forming

The COW method needs a fast burning pistol powder to work well. You need to play with the ratio to get it just right (Lee dippers work well for this). The more powder you add, the more pressure. The more COW you add, the more pressure. If you start with a certain volume of pistol powder to COW ratio, and need more pressure to case form, add more COW and a little more powder, a little at a time (I'd add more COW, since it's the filler and less expensive). Once you have the right ratio, keep using that ratio. You can put some wax on the top to hold the COW in, but may mix up some if you tilt the rifle horizontal to fire it. Most hold the rifle vertical, and chamber and fire it vertically.