I am not a big fan of downloading calibers. Even with attempting this with the 221 Fireball I was never happy with my results on fox. My Tac 20 is rarely used for fox. Very good on coyote and bobcats. When it comes to fox I tear them up beyond what I care for when it conccerning pelt damage. I have over 50 kills on fox with the Tac 20 and rarely do I get one thats acceptable to me. 22 magnum, 17 Fireball, 17 Ackley Hornet, 22 Hornet, 17 Hornet etc. are much better on fox and thats without downloading etc. Bullets, shot placement, distance shot at and so on are still variables that need to be considered as well. Generally speaking though the above calibers are fine for fox. Trust me forget the attack 20 leave that one for yotes and bobcats.