For sale is an old p-mag I had lying around. It was modified for use in AR-10 style lowers. On the front of the mag I went a little deep and it was patched with some JB Weld, and re-sanded. It holds all 20 rounds no problem. It doesn't bind or tilt. It locks solid into place and will drop free. It was never used in the field. It was only tested for function.
Note: It wasn't tested with an upper, because I didn't have one. It was only tested with the lower. There might be more work to do. I think the front of the feed lips might have to sanded down a little bit. There is a forum on ARF about it.
Be sure this is legal to own in your state.
$20 + $5 shipping