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STI Feeding Issue


Seth

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My 2011 has started to have a funky feeding problem I can't seem to nail down. With both 126 and 140mm mags with stock STI followers (wedge style) and fairly fresh ISMI springs the gun fails to return to battery with 1 round left in the mag and the 2nd to last round about 3/4 of the way into the chamber. It feels like the feeding round is dragging on the round below it. And in fact, if you button out the mag and the slide goes to battery.

It runs my SVI/Bolen and my Dawson follower mags 100% from full to empty. It ONLY fails with 1 round left in the mag.

I can't see the trees through the forest. Any thoughts?

Thanks.

Seth

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Well, its probably the mag.

When I get mags where rounds don't feed very well, I polish the feed lips with a stone. If that doesn't work get a very pristine piece of brass, load it into the mag, then slowly take it out. Check it for scratches.

Also measure the feed lips with some calipers. I'm guessing that your talking about 40 cal mags, the feed lips should be about .380-.390 apart with slight tapper from front to back.

Craig

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Yeah. Sorry. .40 mags. ALL the feed lips measure within spec. Some are rougher than others, but this seems to be more related to the follower or spring, since they will feed 100% for 15+ rounds, then hiccup.

I want a couple of mags that lock back, which is why I'm using the STI followers.

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Yeah. Sorry. .40 mags. ALL the feed lips measure within spec. Some are rougher than others, but this seems to be more related to the follower or spring, since they will feed 100% for 15+ rounds, then hiccup.

I want a couple of mags that lock back, which is why I'm using the STI followers.

Ya, your probably right about the problem being in the spring/follower. It just seems odd how the jams are in the last couple of rounds. Try putting the stock STI springs back in them. They will be stronger, that is the only thing I can think to do since the spring pressure pushing the rounds up is greatly reduced when the mag is near empty...

If you can make out what I said... :wacko:

Might work.

Craig

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Quick update... after spending more than my share of Beven's time, he gave me some things to look for. Seems that the bottom round is jamming into the bottom of the feed ramp AND the slide is dragging on the round popping up AND the top of the bullet in the mag is dragging on the round chambering.

My non-STI follower mags don't do this nearly as aggressively.

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On Chris Patty's advice, I went to the Grams 13-coil kit for 170mm mags in all my 140mm .40 mags. The STI's will hold 19 and the SV's 20, with Dawson +1's. I'm not going to achieve the Holy Grail of a 22 round mag with this setup, but they always work. Springs last a long time, too.

If you leave the follower unmodified, and assuming the slide stop hasn't been ground down too far, they should lock the slide back as you want.

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