I 've made myself a hand crank syringe pump and use 18 gauge needles and nylon (I think) tubing. The tubing came from empty hair spray bottles. It's not really not that hard to control delivery rate. Below is a picture.

The tubing arrangement is likely to change a little because the clothespin tends to move around on the side of the pot and the tubes don't really point were I want them to. Also, been thinking about changing to a smaller sized needle.

I think the part about the cohesiveness Ron mentioned to you is that the high pressured streams push away the other liquids and allow the salt and silver reactants to combine at a more closely controlled ratio. So, the crystals are nucleated within the stream and then carried away into the rest of the emulsion. You want to have the reactants introduced sub-surface.