Mech19

I took the BB19 step file and fixed a lot of the geometry on it. I thickened the front rails so that they don't fall apart with finger pressure, I closed surfaces and added some fillets where you'd want things to be a bit stronger. I rounded some corners to make it feel better in the hand and added a cut down where the mag release spring is so that you can get support out of it if you accidentally choose to put support up the mag spring hole.