I purchased a G21 Gen 4 last September. I took it to the range and ran about 2000 rounds of ball without a hiccup. Every January, I cycle all my duty ammo and get new stuff (I have several other guns that have duty ammo). My G21 ran steel, aluminum and brass ammo but I got failure to feed (FTF) from my Hornady Critical Duty, Federal HSTs, Winchester PDX1's. Every other round nose dived in my magazines or caught under the ramp of the barrel. I took it to my gunsmith and he polished the ramp. I still have FTF's, just not as many. My G21 does well with Federal HSTs, Remington Golden Sabers and Speer Gold Dots at the moment. I have no luck with my Hornady Critical Duty. I won't carry my G21 in public (as I'm not confident I won't have a FTF at the wrong moment). I'm still researching the possible causes. I've got five Glock OEM 13 round magazines (no modifications). Any thoughts? Thank you in advance.