All of these Coefficients of friction are dry interfaces on aluminum.

Aluminum - Static 1.05-1.35, Sliding 1.4
Steel - Static .67 Slidng .47
Carbon fiber epoxy - Sliding .23 to .68 (gets worse over time)
Self-lubricating Plastic on T-Slot - Static .1.8-2.2 Sliding .16
Self-lubricating Plastic on polished metal - Static .16 Sliding .13

Its apparent that self-lubricating plastic buttons are the best for initial launch performance. Now if you can get them to fall off right away to reduce drag....

There used to be a magnet shop in Fort Collins called Forcefield Magnets. They had a brick and mortar shop but now are just online only ( http://www.forcefieldmagnets.com/catalog/) They sold very strong magnets cheap. I bought two 3/4" diameter disks and two 1/2" disk magnets to use in a rail button application. I installed the two 3/4" disks inside my rocket spaced where my rail buttons were. I then made a set of delrin buttons that housed the 1/2" magnet in the base. I could attach the buttons to the rocket, which was 5.5" diameter and 15 pounds, and manipulate it in and direction just holding onto the rail buttons. My plan, before the rocket core sampled on a test flight, was to launch it with the magnetic buttons. You'd affix a small low profile rail stop to the top of the rail after inserting your two buttons. When you went to launch you'd just adhere the rocket to the buttons. When you launched the buttons would hit the top and be removed from the rocket. Then you'd be nice and aerodynamic during flight.

Edward

I have sketches for a design for retractable rail buttons that would pull back into the airframe as soon as the button leaves the rail. Unfortunately, the spring tension in the current would be compressing the rail between the button itself and a teflon or delrin washer and therefore create unacceptable friction as the bird moves on the rail. Also, I don't have the ME skills necessary to properly work out the design and fabrication of such. Any takers want to help out with this idea or take it over?

Warren