building a shotgun condenser and deplagmator

[Foxfire]

I was at a scrap yard a day or so ago and saw a 4" piece of copper pipe in a large bin and heard it beckon me to buy it. It was about 11" long and cost me about $16. I also have about 20" or so inches of 2" copper I bought on a previous visit. I am thinking of making a product shotgun and a dephlagmator and was hoping for a few pointers. I read some of the previous posts and it seems for the shotgun some have used 1/2" and some 3/8". I am wondering though about the 4" dephlagmator, should I go with 1/2 or 3/4".

Also I am wondering if I should use brazing to set the tubes in the plate, silver solder to set the plate to the pipe and then use non lead solder to set the ferrules to the pipe. Seems I heard somewhere this can be easier since they have different melting points.

If there are any tutorials or other info out there, I would be grateful to have all I can get