I've been messing around with doing core shots today. Still need to figure out proper temps but I think I might have a technique or two that works.
I tried pouring the outside color by hand into the mold then quickly shooting the core color. I think this could work okay on some molds but I couldn't fill the tails on either my fluke or paddle tail molds.
What I've found to work is to hand pour in one half of the mold and dip a piece of wire into the core color and drag it on top of the half already poured. Then just build up as much of the core color as I want, close the mold and shoot the rest of the outside color.
Here are my results from today. Still need to practice!