Magpul 10 Round AICS, has this happened to you?

Magpul 10 Round AICS, has this happened to you? 1

 

EWA Thoughts

Without the Throne

 

Article 2:  Magpul 10 Round AICS Magazine Problem.

Having recently received my Savage Desert Tactical, I headed for the range to push some factory ammo through it.  I had both the supplied 10 round Magpul AICS mag and two Magpul 5 round mags.  Loaded up a total of 20 rounds and proceeded to fire at 100 yds.  After firing 6 rounds from the 10 rounder I got this misfeed.  I had to press down on the bullet end of the cartridge to get the rim end to rise enough for the bolt face to catch the rim.  I had seen this happen to YouTubers, but they never mentioned it, they just fingered every round.  Contacted Magpul and was offered an RMA to inspect and possible replace the mag.  I on the other hand wanted to find out why this was happening.  So I declined the RMA.

Magpul 10 Round AICS, has this happened to you? 3

At home I simulated the feed problem by cycling the rounds through the mag until I got the failure seen at the range.  This happened on the first pass at round 7.  There appears to be a lack of pressure at the rim end of the cartridge.  As the 5 round mags did not have this problem I wanted to see the internal construction differences.

Magpul 10 Round AICS, has this happened to you? 5

Interior view.  The small ribs compensate for the taper of the cartridge aiding vertical alignment.  It will be seen in later pictures that the 5 round springs are as wide as the space available, but the 10 round springs are narrower and have a longer oval shape.

Magpul 10 Round AICS, has this happened to you? 7

The 10 round spring can migrate into the forward part of the well.  If this happen on a partial mag load the spring pressure at the rim end of the cartridge stack will be reduced.

Magpul 10 Round AICS, has this happened to you? 9

Here is the construction of the two mags.  The 10 round mags have longer and narrower coils in the springs, and the contact length at the follower is longer.  I believe this was a attempt to force more spring pressure forward.  There was no effort to prevent the spring from tumbling forward out of column.  Viewing with a light into the 10 round mags spring on a partially full mag shows the spring has migrated to the front in a arch.  When I tap the mag to re-column the spring the mag feeds properly.

Magpul 10 Round AICS, has this happened to you? 11

This is view of the 10 round spring forced into column.  See the next picture for the stable spring position.

Magpul 10 Round AICS, has this happened to you? 13

When the 10 mag is partially loaded the spring is often assumes this profile.

Magpul 10 Round AICS, has this happened to you? 15

 

So how did I fix the problem?

  1. First I tried the 5 round guts in the 10 round mag.  This almost worked, but the spring was too short, and the rounds sometimes dipped down forward and jammed.
  2. I tried the 10 round guts in the 5 round mag without issue except the spring pressure was a bit high.  I will likely trim the spring length some later.
  3. I rummaged through my retired mags for a wider and longer spring and came up with an 6.5 Grendel ASC 17 round spring that was the correct width and depth.
  4. I reshaped the ASC spring ends to match the 5 round follower profile and installed.  It worked, but the mag bulged badly.
  5. This spring had too much tension, and because these mags are not true double stack, the excess pressure wedged the sides of the mag outward.
  6. I then reduced the number of coils one by one until I got enough pressure to lift all 10 rounds.  This thicker spring ended up the same length as the 5 round spring but with greater tension.
  7. I also lifted the top coil several degrees to give enough forward spring pressure to prevent cartridge dive when chambering.

Since I have never seen a metal AICS mag, I cannot tell if they are true double stack mags.  The Magpul is not a true double stack as the cases do not nest one on top of the next same sided one.  This means that the case below provides vectored sideways thrust on the case just above.  Enough thrust bulges the mag to the point of sticking when pushing it into the bottom metal.  When empty, it still will drop free however.

 

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