Does anyone have any experience with SnAgCu solder?

SnAgCu solder has a slightly lower melting point than the Sn-0.7Cu you're presently using, but the biggest problem is that you're not using any flux. I like the hypodermic-type of liquid flux dispenser, as it allows putting a very small amount (much less than a drop is all you need) directly onto the work, but I've also used a toothpick in the past. You also need some tip-tinner/cleaner and perhaps a hotter iron.