Idea 1. Dont use emery paper! If the tubes at fault why wreck the bushes? Couple of things worth doing, check the OD of the tubes at the ends and in the middle, are they the same? (As you measure the tubes revolve them within the calipers checking for round)I had an issue recently with the bottom tube of some cigar pens. After I took the measurements in the middle and at the ends (both) I found that some of the tubes were the correct dim in the middle but slightly smaller at one or both ends. Traspired that the clamping machine that holds the tube whilst they are revolved and cut was clamping the tube too tightly. Closer inspection showed a slight ridge about 8mm from the end, and the tube was ever so slightly triangular where what was something like a three jaw chuck had been used to grasp the tube. The set up tension on this machine was obviously wrong and it was just on a few of the tubes, the kits were obviously assembled from a variety of batches of tube.
I am not familiar with brass tube manufacture, aluminium is the metal I used to design extrusions for so dont know if the methods are the same, but it would be unusual to get a dimensionally defective batch.
If you are still having problems pm me your address Maurice and I'll put a set in the post that you can compare.
