Originally Posted by
hackman
I've read that the extra round causes extra drag on the slide as it cycles, therefore slowing it down and potentially causing problems. Seems logical.
Not really. If you think about it, you have 7 rounds in a 7 round magazine. If it caused drag on the second round, it would have caused similar drag on the first. 7 is still 7.
Originally Posted by
hackman
The problem I encountered was a with a friends Kimber pro carry.
This adds another variable to the equation. It is a short barrel gun (shorter than 5"), bull barrel (again non standard), and a newer Kimber. Kimber has a reputation for finicky feeding. Particularly in their newer guns. Their customer service spiel "run it a few hundred rounds to break it in" is becoming legendary.
Originally Posted by
hackman
It just didn't strip the second round of the magazine.
OK, let's get some clarity here on what exactly is happening. Did the slide make it far enough back to engage the case rim? Did the round move forward any in the magazine? Was the case rim in contact with the breech face? Did it get under the extractor? Did the nose of the bullet contact the frame ramp? If so where?
Methinks there is more going on here than we have info for. Does the gun still have the stock recoil spring? Does the shooter hold the gun with "high thumbs"? Could the slide be dragging on the shooter's thumb(s)?
Originally Posted by
hackman
It was a standard 7 round mag that came with the gun. And it was a nearly new gun.
Doesn't matter. Magazines are made by a third party contractor, and bad batches come out. Try different magazines and see if you can duplicate the problem.
Originally Posted by
hackman
That only happened once, but I've seen other people say they've encountered similar problems and that they don't carry +1.
A reference number of one (with incomplete data) does not a trend make. It appears that folks are being too quick to blame a single round in the magazine on what could be any one of dozens of other possibilities.
Originally Posted by
hackman
The first is a "second round jam". Pressure from the top round of the fully loaded magazine can produce enough drag that the slide does not cycle all the way and fails to pick up the next round, or doesn't have enough "oomph" to chamber the round. I've seen this happen a number of times on the range.
The magazine spring in a 1911 is around 9-11 pounds. The recoil springs are roughly double that. If there's not enough "oomph" to overcome the drag of the magazine then there is a problem elsewhere. There are a couple of detailed explanations of the various feeding problems in the gunsmithing section of the forum. The culprit is likely one (or more) of the problems listed there.
Originally Posted by
hackman
The second failure mode is a "last round failure to feed". In this failure, excessive pressure on the magazine spring damages it, leaving it to weak to lift the last round in line with the slide. You are left with the slide forward on an empty chamber, and one round in the mag.
As already mentioned, this is due to a weak magazine spring. The spring should be replaced when needed. This has nothing to do with whether or not one tops off.
Originally Posted by
hackman
The third failure mode concerns the magazine catch. Pressure from the topped up magazine will cause wear to the mag catch, and can cause the mag to pop out. I've seen this on the range as well.
Again, you are putting seven rounds in a seven round mag. You aren't putting any more stress on the system than the normal design calls for. If the magazine catch wears enough through normal use not to retain the magazine in the well, it was likely thin on specs to begin with. And there should be warning signs long before the catch fails. A top quality one (Wilson, Brown, etc) is around $20. Replace it and move on.
"The 1911 was the design, given by God to us through John M. Browning, that represents the epitome of what a killing tool needs to be. It was true in 1911 and it's true now." - Col. Robert Coates commanding, U.S. Marine Corp Special Operations Command Detachment 1 (DET 1)
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