COPPER TUBE MOD:
The best material to build a MOD is Copper. Copper is an excellent conductor of electricity. Technically it is better than thin walled tin, alloy, cast or aluminum which are not great conductors.
A "NO SOLDER" PV can lead to poor connections and amperage loss if not properly aligned to the adjoining parts. I have experienced this with a mod I bought.
I have just built a thick walled copper tube mod. More like copper pipe. I soldered the atty base to the copper cap and the atty positive directly to the switch. The switch is a 3amp switch. The other end of the switch is soldered to the positive copper head screw, filed flat to fit flush against the head of the battery post with the entire diameter of the screw covering the entire battery post.
All wire used is 20 gauged for less loss. I opted not to use thin 24-26 gauge telephone wire. The negative spring is a thick diameter gauged chrome plated steel. I would have used copper but the copper springs that I have seen are thin diameter and loose there spring tension. I'm sure there are good copper ones but I could not find any. UP DATE: Installed a Copper Hot Spring made for the Silver Bullet.
My view on the plunger is that the contact point would have to fit squarely flush for best contact. If there is any side to side play/movement full contact may not be achieved. So I went with the 3 amp switch instead.
Instructional Details: http://breaktru.com/smf/index.php/topic,162.0.html