The most durable and reliable connection for backer-to-copper is the Blood Run Power Swivel/heatshrink connection method. Based upon feedback from our dealers who perform bulk line winding services, this method proves to be the most reliable connection method for most fishermen.
While we strongly advocate usage of the Uni Knot for our copper to backer connections just for time savings and simplicity, the swivel/heatshrink method is by far the most often used and maintenance free of any connection.
For our recommended usage of the Uni Knot, bend the copper in a 180 degree bend with about 3-4" of copper. Bring your backer up through the "eye" of the bend, then go long about 3" and pinch your backer to the two pieces of copper (tag and mainline). Then "backwrap" the braid or mono tag end around the two pieces of copper underneath your loop. Put the tag end of the backer back down through the "eye" you came up through and slowly draw the knot down towards the "eye". The knot should snug right down to the "eye" of the copper and you are set. In the case of braid, we like to perform two half-hitches with the tag end of the braid before trimming. Trim the remaining tag end of the copper and you have the perfect low profile copper knot. We use and recommend this for both backer to copper and copper to leader connections.
For the swivel/heatshrink connection, the correct swivel is the Blood Run Power Swivel. Simply take your copper end and slide down a 1-2" piece of heatshrink tubing, large enough in size to cover the whole connection when finished. Then, loop the copper end through one eye of the Power swivel so you have approximately 2 inches of tag end copper remaining.
Take this tag end and haywire twist it to the main copper line below the swivel, make sure the twist is tight and compact. This is easily accomplished by pinching and twisting the tag end with the mainline copper as you move away from the swivel. Slide the heatshrink tube up over the haywire twist and up on to the bottom part of the swivel, and apply heat. Do not slide the heatshrink up past the halfway point of the swivel, as it will not allow the swivel to spin properly.
Your backer to swivel connection can be virtually any kind of knot, double cinch, etc.
Your copper to leader connections DO NOT need a swivel or heatshrink connection. These knots do not receive the same amount of abuse and stress that the copper to backer knots receive. A simple Uni knot here will suffice.