I have had and used hexmags for a while in my m&p 15 w/out any issues. Recently acquired a custom stag build and they would not feed and the bolt would only go halfway closed. I could use forward assist to jam it in but obviously something was messed up. I switched lowers and had the same issue thinking it was that. Turns out it was the bolt and the mag that didn't like each other. The m&p bolt would cycle fine in both firearms. I did some googling research and found alot of people had feed issues with hexmags but never really any answers. I started trying to dig in a little a see if I could find out what the issue was. I put some chalk on the mag lips and started testing things out. After a few different tests I could tell it was jamming because the feed lips were a little to thick and the bolt didn't have enough room to go forward in the upper under its own power. I sanded down the feed lips with some sand paper and voila it works perfect in both guns. I didn't have to take off much and most of the sanding was on the top of lips not the inside where it keeps the round in. I know this is such a simple fix but hopefully it helps someone that was in my shoes.

Thanks for posting that. My Hexmags have worked well with my AP lowers other than being a bit tight in the magwell, I'll keep this in mind as I build up a couple other brands here shortly.