I use a 100/140 gun also except for big stuff. I had to make adapters from 5.5bullets to deans and had no prob using the gun.

When you're heating the bullet to tin it, touch the solder to the gun tip - this bit of molten solder on the tip increases the heat transfer to the bullet. The solder I'm holding in the bullet will melt almost as soon as I do this.

Be ready to solder the wire into the bullet, I never turn the gun off and go straight to the wire. I have the holes oriented so I can see when everything liquifies. Then I turn it off and hold until things cool.