You young technology whippersnappers and your new 50 year old soldering guns, ha.
Try a soldering iron sometime. Bucket of charcoal and you're good to go. Ain't ever found a terminal big enough that an iron couldn't handle. Ok, I'll give you it's a little harder to use on a PC board then one of those new fangled soldering pens, but it never wears out. Alright that and it takes a man and two boy to control one.
Just kidding.
206 as others have said, just from your discription, your tip is contaminated.
And to add my input, I use a Weller 40 pen, and with proper maintaince, as mentioned before, I can solder just about anything, heck I've even gotten into aluminum (for use on lipo packs) and silver (really strong joints for items like landing gear and control rods.