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I tried this setup with FM Colt bolt and endomags , was not very reliable as in jamamatic, mostly do to cheap made endomag plastic ejectors that is built into the upper mag conversion. Forget running any cheap steel case ammo, almost 100% failure rate. I had only one out of three endomags that would do better than 50% with brass ammo, not good odds! Changed it over to a FM glock mag lower and bam! 100% function, all problems vanished. Glock mag setup is the less costly way to go, no doubt.
Folks at Endomag say that
"This product is a magazine insert that converts your Gen 2 or Gen 3 5.56/.223 PMAG® housing into a 9mm magazine to use with a standard AR lower and 9mm upper of your choosing with a []Glock or Colt variant 9mm BCG[]."
I'd get the Glock bolt but either shoukd be good to go.