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Glock Mag Deformation - Fixed


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I have been running Glock magazines in my 9mm PCCs since the creation of USPSA PCC division, initially with a Quarter Circle 10 blowback gun and most recently with a pair of CMMG Radial Delayed Blowback frankenguns. I've had great luck with factory Glock 33-round mags in all of these guns, but noted a tendency for the front of the magazine to deform after a period of time:

 

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My assumption is that this deformation is caused by the cartridge nose impacting the front of the magazine tube as it feeds into the chamber. The deformation occurs in the steel magazine liner and is easy enough to bend back into shape, but over time the liner starts to weaken in this area. Eventually, the bend returns after firing as little as one magazine load and is so bad the magazine is difficult to remove.

 

I tried addressing the issue by changing ammo (bullet profile and COAL) but to no avail. In the end, I decided to find a permanent fix by modifying the gun. Here is what I did:

 

1) Using a scribe, I marked the boundary of the upper receiver:

 

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2) I found the center of the area between the scribed line and the inside-front of the magwell, marked it with a center punch and then drilled a 5/32" hole about 0.45" deep:

 

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3) Lastly, I cut a 5/32" roll pin to a length that would create ~0.23" of protrusion, then drove it into the hole:

 

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The photos below show how this modification works to provide support to the front face of the magazine tube, thus preventing the problematic deformation:

 

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At least in my RDB system, the pin does not interfere with the movement of the bolt assembly, nor does it interfere with ammo feeding. Since making this modification, I have seen no further magazine deformation, functioning has been 100%, and magazines continue to drop free under gravity when the release is depressed.

 

I am optimistic that this modification will resolve the issues on my PCCs, and I wanted to share the information in case anyone else is struggling with the same issue. If you have any questions, post them here.

 

 

Edited by StealthyBlagga
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While I never had any mags de-form like yours, I did notice that as I was unloading semi-full mags after a match that occasionally a bullet case would slightly catch on the edge of the mag as I was pushing out the bullet. This got me thinking that if this happened during firing it could cause a mis feed.

So in effect pretty much the same problem as you I think, just not to the extreme as yours.

I solved it by just slightly filing down (beveling) the angle of that metal piece in the mag so the bullet moved more smoothly across it.

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33 minutes ago, stick said:

The concept seems sound.  My only thought would be to ask Do you want a post in front of the bullet?  From the looks of the roll pin, the top of it is ever so sightly above the mag.  Is that really safe?  Maybe @TRUBL can chime in.

That post is there only supporting front mag lip, rounds will be above the post.

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What he did is very sound......on the post thing, a little higher, like shouldn't be problematic at all.....but if you are concerned, it can be lowered a little bit with a dremel easy enough. 

 

Side note......I was at a match once where a guy did blow out the front of his magazine.....we had to unload it the PCC (of course) then take it to the safety area where one guy held the rifle with two hands and another pulled on the glock big stick with two hands......was a total tug of war going on!!

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2 hours ago, Texaspaul said:

Does you lower barrel ramp on your barrels help also and if you have a lower feed barrel will the ramp work?

The ramp will protect the mag from blowing out. It will only work with barrels that have no ramp protruding back fro the bolt face. IE...our TACCOM barrels or Shooting innovations. On the plus side.....the TACCOM barrels have a built in feed ramp that comes back far enough to protect the magazine from blowing out.

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