The three Snake Tales missions I have beaten so far all got different grades; "A", "AB", and "C". Are these grades dependent on the ending you get? What the hell is "AB"?

Wow, Snake Tales is hard! Playing without radar is a first for me... although now I feel like with radar I could really tear through the main game. It's kinda like putting doughnuts on a baseball bat before stepping up to the plate, isn't it?

Anyway, yeah. What do the grades mean?

Pretty sure there aren't grades,there just story A,story B,C etc,so once you save it shows which ones you've beat.

Yeah, the Tales are like this.
A Wrongdoing
Big Shell Evil
Confidential Legacy
Dead Man Whispers
External Gazer

Pretty nice, huh? They are just the names of the Tales really, they don't mean anything. When you complete one, you will get the M9 on your next playthrough, which tends to make things easier.
No ranks for these. But, you could go for stuff like perfect stats and fast times. Snake Tales really aren't that tough, I have them memorised really, and have decent times and stats on all of them.
You get used to it, and the actual gameplay is only on hard difficulty, which isn't too tough for me, just keep playing, and you'll be fine with it too. :D

Try the boards we have here if you like, some nice times, and great videos from Brazilianjoker, Adnan, and even some insane dream targets set by AmaebiUniO.
http://mgsforums.com/index.php?showtopic=20878&st=0