[metelin]

hitjohn makes some very good points on open versus enclosed track but if you still want to do enclosed i see no reason to use metal. it would be hard to machine the top open (unless you have propper tools) and it will be noisy. an all wood track is just fine but a plastic like delrin is best but if i were i would just do it open, the gun will be much more useable with it. enclosed tracks are best for big guns with lots of power to be used in open water only because the shaft needs to exit the track completely before it stops otherwise it will damage the track. enclosed track should not be used for cave hunting for example.

steve