Use drum spring instead of the mag spring. Drum spring with constant force is much cheaper and easier to source, also space and weight saving.
0.1 x 5 x 600mm Constant Force Drum Spring
Only done 7 round and 13 round mags.
Test shows the 13 round mag's capibilty increases to 15 round.
Category: Mechanical ToysThe author marked this model as their own original creation. Imported from Thingiverse.