Fire Form with Cream of Wheat.
My procedures for fire forming wild cats and making 340 WBY and other magnums from Win H&H brass is as follows. (H&H brass is tough and much cheaper) Find the water vol. of the case to the case mouth in gr. Use 25% of that weight 700x shotgun powder dropped in the case. Fill the case with C.O.W. in three stages with a powder measure. Like fill to top, compact with drill bit, fill to top again, compact with bit, fill to top again and final compact.Use good hand pressure for compaction then seal last 1/4" with Crisco. Lightly rub the outside of cases with Crisco that is left on your fingers.
You can do a super bore-cleaning job by swapping the bore with Shooters Choice every five rounds if you wish.
It is best to fire form with the case tight against the bolt face and with either solid shoulder contact, a second shoulder or jam the case into the neck transition if you have a long case that needs to be trimmed. The case length for that is by trial. Usually 0.015" longer is enough.
If you have head space in a case not to worry the Crisco lube allows the case to expand in both directions but should not exceed max head space. Perhaps 5-7 thou.
Usually the powder weight needs to be upped a bit on some brass seldom more than a 1-1/2 gr. I have literally formed thousands of cases like that with no harm to the bore or guns.
When fire forming Wildcats cases that have been extensively modified in the neck and shoulder, they should be annealed for a good fire formed fit and to keep the shoulders from cracking. Most simple fire forming jobs do not need annealing.
Before loading up a large amount of cases you should test fire and inspect one or two cases and make loading adjustments if needed.
Annealing and fire forming procedures are else where featured on my web site. To compact the Cream of Wheat I use an old golf ball with a fitting drill bit drilled into the ball. This also makes a nice files handle with the right size hole.
Fire forming is best done out door; the report is like a 410 shotgun. Discharge must be in a safe direction. All rules of live ammo apply. Keep an eye on barrel temperature, do not over heat barrel by firing too fast.After fire forming clean chamber and cases with methyl hydrate and barrel with your favorate solvent.
Note:This system can also be used for expanding the necks to a larger caliber, like a 280 Rem to a 338/280Rem AI, or a 300 Win Mag to a 350 Mag. I have never done this but readers have said it works well.
Warning:Under no circumstances should bullets be used with the above method. Use only as described above.
Fred the Reloader