Ash, females are supposed to be 2-5 and males 6-12. I've heard a few different estimates so thats just kind of an average of all that I've heard. Make sure that the snake is not clamping down on the probe when you do it, apparently bloods do that a good bit. As far as tail length, spurs, and growth rates, they dont seem to have anything to do with sex's in bloods. Females are "supposed" to get bigger but you could have a big male from a clutch. I've got a little trio and the male is like twice as big as the females. Also have a pair that probe correctly and I have visibly seen hemipenis on the male and homolongs on the female many times. They grow at the same rate and spurs and tail length are identical. The best way is to probe it I guess, or if you can somehow get it to evert it's privates that would be even better. Good luck bro.
J
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"It's my snake, I trained it, so I'm going to eat it!" - Mad Max, The Road Warrior