I have mostly fireformed using either the end result bullet or cheap stuff if I have it laying around. I've also tried using the Cream Of Wheat method I've read so much about. I've always been rather leery of gunking up my chamber and bore with burned-on wheat residue. I haven't seen signs of this, but it seems it could happen, so I've only done the COW method a few times. I did a couple .219 Donaldson Wasp from 25-35 cases, and they seemed to come out OK, but then I went back to using bullets, mainly because I didn't want to gunk up the barrel.
The last time I tried it, a few days ago, forming 6.5-06 Imp 40 from 270 Win, using 4.5 gn Tite Group, it fireformed the case OK, but the case, especially around the shoulder, was packed with hardened COW after firing. I scraped on it for awhile with a dental pick, then ended up soaking it in hot water for awhile, and finally got all the junk out of there after quite a bit of work. That was the end of COW for me..
Have you folks seen this? Did I do it wrong? I put the powder in, then filled it to the neck with COW, then stuffed a bit of paper towel in on top of the COW, and fired it. Was it because of the sharp shoulder?
I'd rather not waste bullets fireforming, but I'm now even more leery of the COW method. In Ken Howell's book, "Designing and Forming Cartridges", he makes extensive references to using the COW method for all the fireforming he talks about.