That data doesn't make sense but it's what's out there.

Lots of times lead bullet data is kept well below max pressures for a cartridge, but using the same load data for .38 and .357 is just odd. For some reason Hodgdon to take the easy way out and use the exact same data for the 2 cartridges even though the pressure will be even less using a .357 case. I'd guess 4.2 TB is close enough to the max you can fit behind the bullet using this powder and that adding more just doesn't make much of a difference with either caliber.

I've heard you can't get enough Trail Boss into a case to cause pressure problems. Once you start compressing it it becomes erratic, not dangerous, just erractic. This was from someone who had supposedly talked with Hodgdons reloading technicians. However that could be completely wrong for all I know.