TP return from ranged attacks is calculated by combining the delay of the weapon and ammo together, and using the combined delay in the standard TP equation.
Delay Tactical Points Any Store TP you have
0 - 180 5.0 + [(Delay - 180) * 1.5 / 180]
181 - 450 5.0 + [(Delay - 180) * 6.5 / 270]
451 - 480 11.5 + [(Delay - 450) * 1.5 / 30] X {1 + (.01 X Store TP)} = TP per hit
481 - 530 13.0 + [(Delay - 480) * 1.5 / 50]
531 - 999 14.5 + [(Delay - 530) * 3.5 / 470]
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http://wiki.ffxiclopedia.org/wiki/TP