I ended up making a double sided press tool. The one side slides snug over the male conector and the other slides over the slightly larger female conector. Then using a small hammer with a light tap I pressed each bullet into the plastic connector with the tool!

I used a short piece of aluminum bar stock & machined each side in a lathe to a few thousands over the male bullet on one side of the aluminum bar stock and then a few thousands over the female bullet on the other side. Then I shrink wrapped the tool to insulate it when pressing in a hot connection. It sure made pushing the bullets into the plug easy. Castle should of included something along the lines of this for the multi pack. Lol

I'd recommend against bullets for frequent disconnect applications, the "banana spring" wears out and the connection becomes poor.

I'm a deans guy personally, if I need a battery connector I use deans, even on 12S helis. they don't even get warm, last nearly forever and are compact.