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Mag catch channel issue


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So a while back I purchased a upper lower combo form a local vendor and it sat in the safe for a while. I recently started to build this thing putting it together and I have the lower all but finished, I install the the mag catch and button and am function testing it and I notice that the magazines will pop out if tapped on the side of the magazine and if the magazine is loaded they will literally fall out from shaking the gun. I noticed that the mag catch sits out proud of the receiver by about.030 and the part of the catch that is supposed to engage the magazine barely touches it and the catch is screwed down as tight as it can go. Its actually other wise a very nice upper lower combo aside from this issue so my question is if anyone knows if there is a local machinist in Washington state that  would be able to machine out some material of the mag catch channel so it can sit flush and engage the magazines better. I've tried several different magazines and mag catches and the only one that doesn't drop completely free are P mags but it appears that the catch is just catching on the polymer and digging in to the magazine and I don't typically use P mags anyway. Any advice for a relatively new AR 308 builder?

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6 hours ago, OldGregg said:

I noticed that the mag catch sits out proud of the receiver by about.030 and the part of the catch that is supposed to engage the magazine barely touches it and the catch is screwed down as tight as it can go

Are you positive of this, it's in as far as it will go?   Push in on the mag catch button with a punch (or an ink pen, whatever is handy) and push that button in even further than you could with your finger.  You'll be able to get another couple rotations on that mag catch that way, and tighten it up more.  More spring pressure (preload) on the spring, deeper sitting mag catch to grab the mags better.

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12 minutes ago, Albroswift said:

pull the bolt catch off and you can get even another turn on it.


You won't have to remove the bolt catch, if you use a punch/pen/whatever to bottom that button, and coil-bind that spring.  You'll be able to get all the rotation that you'd need that way, even with an AR15 catch in a .308AR.   :thumbup:

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Sorry about the lateness of my reply but answer some questions:

Jtallen83: I'm familiar with the catch you're talking about and it is not the length of the rod that is the problem as much as how deep the channel is and how much of the surface of the actual catch that can engage the magazine.

98Z5V: I have tightened the catch down as many twists as it will go. I pushed the button in as far as possible and tightened it till it would no longer clear the the outside of the lower while twisting and I am still encountering this problem.

Albroswift: I might have to take you up on that if this can't be remedied by what hopefully is my ineptness at building this thing. I am in Seattle down in the city.

Beltfed: Thank you, I searched but for some reason was not able to find this article

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Almost finished the build around the ported sig 5.56 barrel.

Dabbed a little 44/40 original cold blue in the ports 

Anderson upper and lower

Toolcraft BCG

Not sure where the tiny little millspec looking buttstock came from, been laying around for 20 years or so. 

MBUS sights only at this time

Aim Sport guard, I was impressed with this, self aligning, lightweight, clean looking.

Didn't have a buffer detent spring or pin, the rule that if you dig deep enough in the parts bin you will find what you need didn't quite work out, stuffed the spring and buffer in it anyway and snapped her shut. 

Parts bin almost empty. 

Range in the morning with this and the 308 and and...









Edited by Albroswift
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