12 Round Mag issue

[Indy_Tim]

Is there any trick to getting 12 rounds into a 12 round Mecgar magazine?  I just bought a pair of them for my 40P from GregCoteLLC.  These are the ones that come with the SP01 base plates installed.  When I load them, no matter how hard I try, I cannot get more than 8 rounds into them.  It seems like the rounds are jamming up down inside somewhere.  When I remove the spring and manually stack the rounds without a base plate, they bring the base of the follower to the exact bottom of the mag, so the whole spring would need to collapse into the follower for them to work.  Maybe that's normal.  But, neither of the mags seem to like more than 8 rounds and often jam at 7.

Do you think they just need broken in?  I've disassembled and wiped them down , but still nothing.  It's a little frustrating to spend $60 to replace your 10 round mags with 12 round mags only to be able to load just 8 rounds.  It's not a good return on the investment for those

Any ideas?

[chiddly]

I just bought 2 of the same mags from the same company, great product with great service. I myself could only get 10 in by hand the first range trip but they loaded 12 just fine with the help of a maglula although very tight. I had zero issues with feeding or running with 12 rounds loaded. They are getting easier but still need a maglula to load 12 rounds. These are running in my 40p.

[CZDad]

Maglula helps tremendously.

[Indy_Tim]

I have a maglula and it was jammed hard enough that I was denting the side of the case with the tip of the Maglula loader.  I'll disassemble them again and make sure the mag tubes are clean and slippery.

[Indy_Tim]

I figured the issue out.  When I measured the 10 round mags and compared them to the 12 round mags, the 10 round mags are about 5 thousands longer, front to back.  Then I measured my reloads and found them to be about 4 thousands over spec.  The overly long reloads worked fine in the 10 round mags, but the shorter length of the 12 round mags would cause them to choke down about at the 8 round point.

In short, I got sloppy with my reloads and did not keep an eye on the COL as I should have.  The 12 round mags load just fine with spec ammo.