I have one I made out of a 20 rounder. I put 5 rounds in the mag, slowly slid the floorplate back............
WATCH OUT FOR THAT SPRING ELMO!!!!!!!!!!
After I got myself up off the floor, went to the bathroom to change the shorts, I carefully measured the distance to the bottom of the follower. I then took another spare mag & removed the follower, carefully profiled a small block of oak to fit the underside of the follower. I then cut it off at the appropriate length (can't remember the actual length).
I then epoxied the wood block to the bottom of the floor plate after shaping it to fit inside the mag spring. After it was all dried, I slid the follower back in, shoved that stupid, mutherphu**in,, absolutely won't go in.......... GAWD AWFUL SPRING!!!!!!!!!! into the mag body & slid the floor plate home.
Should have seen the local game warden when I had it out in the field. He did ask about it, I showed him, 5 rounds in, no more. He thought it was kind of cool.............don't know if it was the FAL or the mag. He hadn't seen a "black rifle" in the field before. But he did kind of like it.