>>64461368
Do you KNOW that specific manufacturer's 4140's composition is exact, the heat treating is full, etc?
With production there's always a range and tolerance for everything. Some mills shit out everything from both extremes of the spec range, some are more tightly controlled.

It's like when I'm handling galvanised road works and you can tell when Gregory fucked up their tank mix or had the dip too cold or were rush processing and didn't drip drain the pieces long enough or a mix of all three.