Colt 9mm magazine feed question

[p7fl]

Not sure of the correct wording for this question. I was sighting in a newish Colt AR in 9mm.

End of the session using a Metalform 20 round magazine,  with the same cheapo ammo used all day, I had a number of failures to eject spent rounds.

I figured it was a bad mag. But, in reflection is the 9mm AR is sensitive to resting the magazine on a flat surface. I’ve always used my 223 mags as a rest point without issue. But found that any push on Swedish K or SW 76 magazines forward or back would lead to mis-feeds.

Any standard experiences with feeding while pressure is on the  9mm AR magazine?

[Tampa-XD45]

I've had no issues resting my PSA 9mm AR on Colt style mags.  In fact, the 32 round mag makes an excellent bench rest.  Mine has a Spikes magblock but look at the picture below.  A frequent culprit for FTE problems is misalignment of the ejector within the bolt ejector channel.  The setup pictured below is good to go.  Sometimes the ejector has to be bent, or some magblocks have adjustment capability for the ejector.  The ejector should be tight to both sides of the channel without touching.  You can feel if it's touching the channel when you pull the charging handle.

 

 

[OPENB]

I also had to tweek the ejector on my PSA dedicated Colt style lower by using a nylon headed hammer and a couple strikes to move it to the right a little. 

[jrswanson1]

Part of the problem is there's no standard for these magazines.  I've experienced similar problems with Colt magazines in my CMMG.  The Colt magazine sits higher than the ASC magazines I have, so sometimes the magazine pushes on the bottom of the BCG, slowing it down and preventing ejection of brass.  Also, lack of lube can cause the BCG to drag, preventing ejection. 

[RevolverJockey]

I have a DDLES lower on my 5" SBR use only metalform 32 rounders. I regularly shoot sub minor 124s with fast powder and have the plug in the bolt and an over spec'd buffer made of tungsten copper heavier than any buffer I have ever seen and XP Wolff spring. I have never had any ejection issues so poor ammo is the last thing I would suspect. I shoot suppressed if that makes a difference but by normal ammo land in a cute little pile at 2 o'clock from the rifle about a foot away. Factory SB is more like 3 o'clock 7 feet away. 

Lee