Selection of method in AASHTO T99

[ThePilgrim]

Evidently, I've been doing this so long my brain has fried. I was reviewing the AASHTO T99/ T180 procedure. I find the four methods described, but no indication of when to use a specific method, except the rather unhelpful,"If no method is specified, the provisions of method A shall govern" Can anyone provide some guidance on when to use each of the four methods ( A-D)?
I know that ASTM D698/ 1557 has instructions for when to use each method, but they only have three methods, not the 4 of AASHTO. I used to think that AASHTO and ASTM were identical on these tests, but it does not appear to be so.

 

[Rjeffery]

the selection of the method (A, B, C, Or D) is based on the gradation of the soil. The ASTM procedures removed Method D in the early 1990's I think.