Sorry, i was a bit hard to follow there. I use a paste consisting of water+flux and tin/lead powder that i use for get the "real" solder to bite. I basicly put the paste on and as i heat it, it first dries and then starts to flow, perhaps adding some additional paste to get it all tinned and then i use a 4 or 5% silver/tin alloy for the soldering. If mounting a sight and one has a tight fit, it is possible to only add the paste, clamp the parts together and heat it, if tone properly it bonds hard.