Del, since the 256 was once a factory round, it's not a wildcat, but would be considered obsolete, since the majar ammo companies no longer load ammo or make brass. From your post you seem to know that brass is very easy to form from 357 mag cases.
The way I use the 256 is a little different then most people. Most people use a jacketed bullet and try for as much velocity they can get, which will produce excellent performance. But that is not what I need. I'll explain. When I hunt ground hogs, I use a rifle with a bipod or a 6mm TCU contender with a rifle scope, and I use a camera tripod with a cradle on it to rest the gun. Both work great, but are slow to get into action. I carry a second contender, with open sights, in a belt holster. When my partner and I are walking to our shooting spots, we often jump ground hogs along field edges, when rounding corners, or dips in fields. Most of the time the range is less then 50 yds.. Many times we are spoted by the ground hogs, and have little time for a shot before the hog dives. I don't have time to set up the rifle or the 14" contender, so the open sighted 10" barrel is drawn from the holster. I tried a 22 LR but it wasn't powerfull enough. I've tried all the top ammo, and with chest cavity shots, it was about a 50/50 chance that the ground hog would be stopped or run to the hole. (I havn't had a chance to try the new CCI Velocitor) The 22 Hornet is too loud, sometimes the action is so fast that I don't always have time to get the headphones on. I don't need more hearing damage then I already have.
Enter the 256. I did some research and the 256 seemed like a good choice. I use a cast bullet, Lyman #257420, cast of wheel weights + 2% tin. I hollow point them in my lathe, they weigh 65 grs.. 8.0 gr. of IMR 4756 and Rem. 7 1/2 primer completes the load. The velocity from the 10" barrel is 1875 fps.. With an Aimpoint on the barrel, the accuracy was about an inch at 75 yds.. I never put a rifle scope on this barrel to see just how accurate this load is is, but it seems very accurate. When I had the Aimpoint on the barrel, I once put 5 out of 7 shots on a ground hog, that was out in a plowed field, at 300 yds.. The bullets were out of power at that range, but the accuracy was there. At 200 yds. the killing power is good, but usually I don't shoot over a 100 yds. with open sights. Under a 100 yds. the killing power is very good. I shoot about 75 ground hogs with it every season. The muzzle blast is not much louder the then a 22LR.