See "HANDLOADER" Feb2009 issue;................
Explains changes in components (bullets and primers) and powder itself.
Some of the published data/loads in older manuals using current lot#'s of powder and bullets are significantly over-pressure to the point of being unsafe.
CYA by the companies involved..................
In late '70's and early 80's when I was poor, and needed to load .357mag factory duplication loads for practice/qualification, I used a lot of Bluedot. Gave similar velocities to #2400 but 30% lighter charge, with a 155gr Cast SWC. But, in mid '80's I started seeing a lot of pressure signs;(cratered primers, sticking cases) with same load I'd been using for some time, and quit using BlueDot, and went to Unique with further charge reduction, but perhaps 200fps reduction. A large Atlanta Metro PD (East Point PD) using Mod66 and M19's started having cut frames (topstrap at forcing cone) using 125gr jacketed bullets and 10.0gr of BlueDot in department reloads. This was one of the "issues" that led S&W to come out with the M686.