This is what they did originally, activating their timers so that they should be right next to you when they detonate, but people complained that grenadiers were guaranteed killers and were OP. Hacks should still be able to target things, but because of their nerfed targeting mechanism they can either be man-moded to death or be ran away from (their algorithm actually tries to place you so that if you run away you end up just outside of the explosion range).
As such I’m not so sure about making them slower; they already are actively trying to miss you, and if they slow down any then they essentially become a non-threat to the player (even with a perfect targeting algorithm) who will just be able to go “oh, a drone runs away and laughs”. Remember that players can run, which essentially gives them 200 speed for all intents and purposes while running away.
For the on-contact issue keep in mind that any changes to hacks apply against you as well; grenadiers will throw them at you and if you don’t want them exploding on contact with your face then they shouldn’t be exploding on contact with a zombies (though the targeting algorithm could probably be changed slightly so that they tried to maintain a distance of 2 right up until the very last moment to make them a little less vulnerable to things just trying to nom/whack their face).
And yeah, weight/volume seems kinda mixed up there; generally I always figured it should be approximately the size/weight of the ammo it is carrying plus a little bit more, and if they aren’t then that’s something that needs to get fixed (though the broken thing is probably part of the corpse processing code, and as such might not have such an easy fix).