I'm cooking up some arrows using the 3 Rivers calculator and when selecting a string, they have b50 or FF in various configurations. I'm using a BW PSAX 49@28 62". I selected a 14 strand FF as my string and worked up a nice FOC arrow, and it's very close to my heavier BW longbow arrows, only an inch longer. Am I good or should I select a different string?

I don't use a computer at all, just an iPad, so operating system compatibility issues arise with the spine calculators I've used in the past.

Stick with the FF string.

Black Widow bows all come with a 14 strand FF string. So you are good to go.

I agree stick with the FF