it has a LOT To do with mag spring strength. I had one for a while, and it only worked reliably with 3 out of 10 mags I owned.Glock mags DO NOT work on the EPC. The last round will not feed every time. I contacted AP and they suggested I switch to Magpul and I have had zero issues Since. AP parts are top notch IMO. I could not find AP BCG or Barrel when I built mine so I went with Faxon which is equally made as AP. Not had a lot of rounds through mine yet but was my 1st build and was super easy for an novice. Maybe parts have dropped an little but I was in the $1200 range. You could cheap up a few parts probably to get into the $1000 range. Good Luck with the build.