This is for you experienced reloaders, and before you tell me that it's unsafe to do this, please read the following PDF file right off Hodgdon's website. Don't try this with any other powder than IMR's Trail Boss though as TB's the only powder in the world that you can safely do this kind of load development with.
Trail Boss is a unique powder that was developed originally for the Cowboy Action shooters to produce light, low recoil handgun loads with lead bullets. Some guys started experimenting with it in reduced loads for rifles both with cast lead AND jacketed bullets.
Hodgdon (who now owns IMR) also began experimenting with it and came up with the info in that PDF file.
Turns out you can't stuff enough TB into the case, no mater what caliber of handgun or rifle round to even come close to the SAAMI max pressure rating for it.
If there's no Trail Boss data published for a particular caliber, you can safely develop your own using the following formula. REMEMBER! IMR Trail Boss is the ONLY powder you can safely do this with. DO NOT attempt to substitute any other powder for Trail Boss. The results would be disastrous to say the least!
Take whatever cartridge case you want to develop the load for, figure out where the base of a seated bullet would come to in the neck of the case. Fill the case to that level with IMR Trail Boss and weigh that powder. That charge weight now becomes your MAX load. Multiply that weight by .7 to find the 70 percent point and that weight becomes your starting load. Work up from there in .5 to 1 grain increments until you find the best accuracy for that caliber. Bullet weight is immaterial. As long as it's an appropriate bullet for the caliber, the starting & max loads will still be the same. According to Mr. Reiber (Hodgdon's head of ballistics) the best accuracy will occur somewhere between that 70 and 100 percent case fill.
The Trail Boss granules are so bulky that for example the starting load of 2.7 grains of TB fills a .38 Special case to just about halfway. The max for a .38 Special is about 4.2 grains of TB. You simply CAN'T pack enough TB into any case to overcharge it. There's an article about this in the 2010 Hodgdon reloading magazine/manual on page 50.