the coffee beans you use HAVE to be robusta
store bought arabica won't do the trick ...
have fuN !
I use no more than three, with two being my "work horses" (XTol for HP5 in MF and 35mm, also used for slower films when I use them. HC110 for TXP320 in LF)
When I need to push, then TMax works fine.
I try to use them all one-shot, so that I can rely on them.
there are 2 different kinds of beans, arabica ( shade grown, expensive, yadda yadda yadda )
all the high grade coffee shops sell that ( except in the espresso but that's another thread )
you will have to hunt around the internet to find robusta beans. a lot are grown in vietnam
and indonesia, but still there are some varieties in african and central/south america ...
i have lots of them, and would be happy to sell you some ... :)