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Help with a few econo build bugs

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I have an econo build with dedicated colt mag lower that has some bugs to work out.  Shot it for the first time today.


Colt mag lower

Kaw valley bcg

Faxon 16" barrel

Elf AR9 trigger.

Aero upper receiver 


The two main issues I encountered are fairly common so I'm hoping to get a few pointers.  


First is ejection issues, every couple of rounds the spent casing would get caught inside the upper and not eject.  I think this is primarily because of the mil-spec Aero upper.  Would  a swap to a Taccom upper receiver help here?  Rounds will eject fine via use of the charging handle.


Issue number two is seating the colt metal form magazines on a closed bolt.  This is a known issue, anybody find a solution??  Read in another thread where the poster had filed 0.01 to 0.015" off the upper portion of the magazine catch cutout on the magazine itself so that it would sit lower within the magwell when inserted.  The loaded rounds are hitting the bottom of the bcg I think.  I was thinking of filing the top of the magazine catch itself so I wouldn't have to modify all of the magazines, and since the mag catch is pretty cheap to experiment with...  What has the peanut gallery found to work??  


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No experience with Colt mags, but I used an Aero upper with no ejection or reliability issues at all.  This is with a Foxtrot Mike BCG, milspec lower and a Stern Defense Glock mag adapter.  I agree that you may want to look into the ride height of the ejector compared too your BCG.

Edited by MoRivera
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What's your load? I found that with light 147gr loads I occasionally had failures to eject like you're describing. Bumping up the powder by a couple tenths fixed it. 


The tough reloads are not something that you can really fix unfortunately. I got to the point where if I knew I was going to have to do a reload on a classifier or at a monster match, I'd plan my stage around having to do a reload to a partially-loaded mag. I'd recommend getting a big stick and just never having to reload except on classifiers 😂

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You almost never have to load on a closed bolt except a table start. The easiest answer is to buy an extension and download your mags. Hell, they make +20's. So even for a 32 rd field course with a table start you should be able to load up with a +10 or a +20 and download by 5-10 rounds. 


Inducing slop into the magazine and/or changing to a steeper angle of entry for the cartridge doesn't seem like a good tradeoff. 


As to ejection:

- Make sure the ejector is close to the bolt and not beat to crap

- Check your EXTRACTOR tension and cleanliness. Plenty of YT vids on it. Not enough tension can mean the round isn't held to the bolt well enough for the ejector to SMACK it out of there. 


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