Well this is the reason (little odd, just an enquiry to see if it could be done): tranquilising darts. My idea was you could shoot something in the wild, the dosage is not strong enough to immediately prevent much movement as the point is for it not to be lethal, the hunter then tracks the animal as best s/her can. However depending on the animal a short range tracker could be useful (it going into a den, hiding in a thick hedgerow, etc). But often animals will knock the darts out or they will fall off quickly, but if the dart is made out of two parts: tracker and needle, liquid and feathers, then the latter part could be dislodged easily but a small tracker and the needle being mostly in the animal the former part might not be.
I know, I know. Lame idea, but I thought it wouldn't hurt to find out if such a thing was possible (the tracker, the rest of the concept would be possible if the weight distribution was acceptable).
And sorry, I meant 7.5mm³, sorry for the mistake.