This is a remix of https://www.thingiverse.com/thing:2805177. I opened up the "mag well" to fit a wider variety of magazines. And added the option to install a mil-spec AR magazine catch/release. Works with 300 Blackout as well. Further updates to come.

If printing in PLA you probably want to use a lot lighter spring than the catch comes with to help keep it from deforming over time, this area may need more work.