Bullet Connectors - flux or not to flux?

[What's_nitro?]

Flux-core 60/40 solder & 60W iron works fine for me. Unless you use solid plumbing solder I don't see a need for additional flux, but, in that case it would be necessary.

[georgec]

I also build and repair stained glass, and if you want your solder to flow you must flux so I do the same on all welds always seems to give a nice wet shinny joint.
My .02 worth