Here is an article I used to get started.
Brass, Bullet Lube and Breakfast Cereal?
by Stan Debick
My 309 JDJ barrel showed up about a week into the new year. I set about getting all the items necessary for it to make its first trip to the range. The usual things like brass, bullets, scope, rings, base, dies, etc. The only thing is that the brass for the 309 JDJ, like most wildcats, is not available from any manufacturer. In this case, the brass had to be formed from 444 Marlin cases. I could have simply formed the brass using a 308 Winchester die according to the instructions provided by SSK and then loaded up some reduced loads to fireform the brass, but that would put my load development back by a few days. I would have to head over the range and fire off 100 loaded rounds and then head back to the bench and reload my test loads before putting up the test targets. Instead, I decided to try a technique that I have read about several times in the past - Cream of Wheat fireforming.
Using Cream of Wheat lets you fireform your brass without using bullets and it lets you develop sufficient pressure for fireforming using a greatly reduced powder charge. Since there are no bullets to worry about, I could fireform the brass from the comfort of my woodshop by directing the shots out the door into a nearby snow bank. I sat on a stool next to the fire sipping a nice hot cup of coffee while I fired 100 loads. The basics of constructing a Cream of Wheat fireforming load are as follows:
1) Prime your brass with a standard pistol primer.
2) Charge each chase with a reduced load of fast burning powder.
3) Place a wad of toilet paper on top of the powder and tamp lightly.
4) Fill the case to the base of the neck with Cream of Wheat
5) Top off with either a second wad of toilet paper or a dab of bullet lube.
Let's take a look at these steps in a little more detail.
All references that I have seen recommend using pistol primers. While I can't imagine that pressures would get out of hand regardless of what types of primers were used, I chose to stick with what I had read and used standard pistol primers. My results were good and I will continue to use pistol primers in the future.
The powder comes next. This, as stated above, should be a fast burning powder. Most procedures that I have seen call for Bullseye. I have also seen instructions that utilized Unique. Quite honestly, I believe that any powders with similar burn rates would produce similarly satisfactory results. The basic method for determining the charge weight is to fill a case with the powder that you choose to use and then weigh the powder. Take this weight and divide it by ten to determine the charge to use with the Cream of Wheat. For example, if you determine that the case will hold 40 grains of Bullseye, then the charge weight that you should start with is 4 grains. This is the starting load. It may or may not be enough to completely blow out the case. I experimented with each of the powders that I tried and found that, on average, I needed to go to around 13% of the case capacity to get good results. I tried Bullseye, Unique and Power Pistol. All produced well filled out cases at a 13% charge. I am deliberately not listing actual charges. Brass varies from lot to lot, and the brass that you use to form your cases may not have the same case capacity. Of course, different calibers will require different charge weights. Keep in mind that you have a little more latitude in regard to charge weight when working with larger cases like those based upon 444 Marlin brass. If you intend to fireform smaller cases remember that very small increases in the powder charge can result in large increases in pressure. The bottom line is to proceed carefully until you find a charge that completely fills out the case.
After you know what charge to use, charge all of the cases in a loading block and then top off each with a wad of toilet paper. For the 444 cases you will need about 1/4 of a sheet per case. I stacked up about twenty squares of paper and tore them into quarters. It is much easier to tear a stack of twenty sheets than it is to tear each sheet individually. Crumple up a quarter sheet and lightly tamp it on top of the powder charge. I use an unsharpened pencil for this task, but if you are working with anything smaller that .30 caliber you will need to use a smaller object. Some people also claim that you can use small wads of Dacron filler as a wad. I have no reason to doubt them, but I did not have any Dacron on hand. I hope that everyone has some toilet paper in the house.
With the toilet paper wad in each case, now its time for the cream of wheat. Fill each case to the base of the neck with the cream of wheat. I poured a little cream of wheat in a cup and then used a small Lee powder dipper and a powder funnel to fill each case. I also used a Lee dipper to put the powder charge in the cases. I have found that these dippers are a very consistent way to measure small powder charges. If you have a set of powder dippers, just experiment until you find the one that will just fill the case to the base of the neck. Some procedures recommend other fillers, such as cornmeal, instead of cream of wheat. However, it has been suggested that anything other than cream of wheat could have a sandblasting effect on the barrel. On this count, I chose to be as safe as possible and used cream of wheat.
Once you have the cream of wheat in the case, you need some way to hold it in the case until you fire it. For this purpose you can use either another wad of toilet paper or a dab of cast bullet lube. Since I had both items on had, I tried both. The toilet paper method requires about another quarter sheet. The bullet lube method requires just enough on your finger to fill the case neck. In my experiment, there was no discernable difference in the final result regardless of whether lube or toilet paper was used. I will use toilet paper in the future simply because it is cheaper to use and less messy than the bullet lube.
Now it was time to fire the cases. As I said, I opened the door on my woodshop and fired the cartridges into a snow bank. You don't need a range backstop, but you are still expelling a projectile. Make sure the gun is pointed in a safe direction. Don't kid yourself into thinking that you don't need ear protection. These rounds are loud, especially if you are going to shoot them from inside a garage as I did. Also, they will heat up your barrel just as regular rounds would. I fired them in strings of about twenty rounds each. I fired rapidly, taking just enough time between shots to verify that the paper wad had cleared the barrel. I did not have any stick in the barrel during my experiment, but I would strongly suggest that you check the bore after EVERY shot. I let the gun sit about five minutes between strings to let the barrel cool slightly and then fired another twenty rounds.
The total time required to fireform 100 rounds was about thirty minutes. Add to that the 30 minutes or so that it would take you to prepare 100 fireforming rounds (after you have your procedure figured out), and you have 100 fireformed rounds ready to go in about an hour. Don't forget to document your procedure. If you do, you will be ready to go the next time that your need to fireform that caliber.