MEAN Endomag is a neat way (IMHO) of converting a standard GEN2 or GEN3 5.56 Pmag into a 9mm mag. My home range has a 3-gun competition limited to no rifle calibers. Berms, liability and etc. I bought a Palmetto 9mm upper with BCG. Using the lower from a customer build (I call the lower Frankenstein), now I have a rifle capable of chambering 9mm. During my search for a 9mm magwell adapter I ran across the MEAN Endomag conversion. Remove base plate, spring and followers from the Pmag and insert the Endomag and reuse the Pmag base plate. BINGO! I now have a 9mm Pmag to reinforce muscle memory but using cheaper 9mm ammo. WIN - WIN INMHO. MEAN explains how to exercise the BCG to slowly shave the conversions soft plastic lips to allow operation. In my case I had to use a sharp hobby knife. With little effort on my part I had two of the three conversions working reliably. The third conversion was shipped with deformed lips, the mold die hadn't been complete filled with material. A email to MEAN with and explanation and pictures and a week later I had a replacement. MEAN has a life time warranty. Off to the range I go. First time loading 30 rounds into the conversions. As expected the more round I loaded the more the spring was compressing. The 30th round took all of my effort with both thumbs to roll the 30th round into the mag. Then the mag would not lock into the mag well! If I lock the BCG rearward the the mag would lock, feed and fire with no problems. Experimenting I found if I load with no more than 20 rounds the mag would lock into the mag well with minimal effort. This 20 round limitation will work of the range's 3-gun. I'm disappointed in the limitation for TEOTWAWKI. I email MEAN and they respond by calling me. I'm the only customer that has reported this problem. When they learn I'm using GEN3 with windows they suggest that Pmag changed the Pmag's specs to allow for the window. Do I have other Pmags I can test with. Yes I do, I'll retest and email them the results. I tested GEN3 with windows, GEN3 without windows and GEN2 without windows. All three Pmag models will not allow the Endomag to lock into the mag well. For grins and giggles I swapped out the Frankenstein lower with a Ruger lower. All three Pmag models will still not allow the Endomag to lock into the mag well. I pointed out to MEAN that I have Lancer magazines that are designed to hold 30 rounds. BUT the Lancer will allow 31 rounds to be load BUT there is not spring compression left to allow it to lock into a mag well! MEAN emailed me back. They will call me this afternoon and have their design engineer on the call too. My Internet search found one reference to a Reviewer's quick mention of "if you don't load 30". Left a comment for the Reviewer for more information.