Just be very careful since the color of your leads is your only means of "Reverse Polarity Protection". You could go "male-female" on one side, and then do the same on the other side. This way they can't be plugged in backwards.
When I solder Bullet connectors, I always tin the wire first with alot of solder. Once it's tinned all the way around, remove the heat and continue to lay solder on it. Create a "bulb" of solder there.
Then I insert the connector into a clamp on a "helping hands" and fill the connector to the bottom edge of the hole you mentioned. A little always runs out that I have to clean up when I put the wire in.
With heat applied to the connector, the tinned wire will heat up and slide right in.
On the larger connectors, I've noticed they don't fill all the way to the top like 3mm connectors do. I think it's OK if they don't. Just so you have a contact patch a little larger than the Cross Section of the wire, it should be fine.
