Pull the follower down a little bit so it's easier to get the little nose from the adapter to hook it.
Pull the adapter over the mag with the nose facing the bottom of the mag
I like to hold the adapter with my middle finger pressing the mag into my palm
Insert your regular speedloader into the hole and hold the magazine at an angle downwards, try not to tilt it to a side, that way you will ensure a perfect double stack
Speedload your BBs
Pull of the adapter
Easy print.
no supports
2 Walls
10-15% infill is enough
I printed it from CF PETG but it should be fine with any filament.