Nice work!, I too use box section for the slider but its cut down the centre to guide the slide. In the machine I am building the cast is delivered nose down, and a open ended slide would allow round nosed cast to just roll out, or drop sideways.
I can see a use for your design in a auto-deprimer !!!! Arrgh no... no more idea's please!!!!
but then again.. maybe later on.... I could.. NO, stop it, I am walking away LA LA LA LA not listening to the internal voices!!