Just a note. These mags are simple (temporary) spring fed mags. I used (cut-to-length) pieces of 3/4 aluminum U-channel.
Plexi-glass for spacer (as its hard but super smooth stuff), home-made springs. Hand cut guide slots. Tiny scews each side to hold together.
The internal bb-ammo feed tubing (just about any thin metal material). BB-ammo push-rod(s) I used 1/8 brass tubing, soldered in small screw
for the lever to slide & lock the push-rod. SIMPLE but effective til' I get REAL equipment to build much better stuff.