This is a AR style magazine insert for chest rigs and other mag pouches or gear that takes AR mags. This was modeled to be fairly similar to the Haley Strategic MP2 inserts. These have a small lip that catches on the mag release stop to provide some positive retention.

To mount this to your gear just stick some velcro tape on the outside of the insert.

To adjust retention heat the insert with a hair dryer and slightly bend the insert. Alternatively you could wrap some rubber bands around the lower half of the insert.

F3d and STEP files included.