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Old November 20, 2013, 10:01 AM   #1
leadchucker
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Kahr PM40 Magazine Problem Revisited.

I found a thread related to this, but it was over a year old, so I will just start a new one. For reference, here is the old thread:
http://thefiringline.com/forums/showthread.php?t=483193

I have been trying to figure out why the slide on my Kahr PM40 sticks to the rear with a full magazine. It has been described as the "round nose dive" problem. It makes the gun ammunition sensitive, and prone to failure to chamber malfunctions. After a lot of studying, research, and comparison, here is what I have found.

Almost every semi-auto non-tapered round type magazine out there holds all the rounds parallel to each other. Normally, when the slide moves forward, it contacts the upper exposed rear edge of the top round, and pushes forward. As long as the round underneath the top round is parallel with the top round, the top round can smoothly be stripped from the magazine in a normal manner with no excessive friction or catching points. The Kahr magazines in my PM40 are not like this.

When these magazines are loaded full or nearly full, the rounds underneath the top round are pointed down. This is obvious if you look at the front of the exposed rounds. It is particularly obvious on all three of my PM40 mags.

When these rounds are positioned this way, it can cause problems. When the slide moves forward, it contacts the upper exposed rear edge of the top round, and pushes forward in the normal manner. But because the underlying round is pointed down, its upper rear edge catches in the extraction groove of the top round. This accounts for the resistance of the slide to move further forward. It also creates a moment, or leverage, on the top round, forcing the front of the round down, and you have the "nose dive."

What is causing this is a loose fit, and excessive flex, of the magazine follower. It cants forward under the higher spring pressure of a loaded magazine, allowing all the rounds except the top round to also cant forward in a nose down position.

To prove this, I temporarily glued a small piece of plastic to the lower rear corner of the magazine follower to improve its fit and resistance to this movement. This greatly reduced the nose down position of the lower rounds, and eliminated the catch in the slide, and the round "nose dive". The flex in the follower still allows some mis-positioning of the lower rounds when the magazine is full, and I suspect that this fix would likely eventually simply cause the follower to break.

BTW, based on the reports I have read, these magazine followers do indeed break fairly often.

Kahr does not acknowledge that it is a problem. In all the reports I have read, all Kahr does to address this issue is to replace the magazines or followers. Although this might somewhat alleviate the problems, this issue still exists.

Kahr's are excellent firearms, and there are plenty of Kahr pistols out there where this magazine follower flex and fit does not cause noticeable problems. It is obvious to me that this magazine follower issue is a design defect particularly in this model. IMO, because of this issue, this gun is not reliable as a self-defense weapon.

Anybody else experiencing these problems with the PM40 or like guns from Kahr?
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Old November 20, 2013, 08:01 PM   #2
wpsdlrg
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Not to contradict you, but I found another route to solve the feed problem with my Kahr (CM9). In NO way am I criticizing your work or the solution you've found, so please don't think so. I simply want to pass on what I found, for what it's worth.

I too had the "nose dive" problem, but only with the first round from a FULL magazine. Every once in a while, the second round would misfeed, but almost always it was only the FIRST round.

After studying the issue, I realized that loading the last round into the magazine was VERY difficult. (I mean the last round for a full magazine, thus the first round to be chambered.) I came to the conclusion that the mag spring might be too long - and the coils were closing completely, thus making it very difficult to get the last round in. Also, because the top round was under such high pressure (jamming it against the feed lips), it would tend to stick and nose dive, rather than stripping smoothly out of the mag.

So, having several magazines on hand, I decided to act on my conclusion. I started with one of the standard 6-rounders. I cut ONE coil off the bottom of the mag spring. When tested, feeding was improved, but the problem was not gone completely. So, I removed another coil from the mag spring. Voila - problem solved. The mags have never mis-fed since.

I also experimented with the 7-rounders. I found that removing 3 or 4 coils from the mag springs was needed, in order to ensure reliable feeding from a full mag.

That was early in my ownership of the CM9, but just after I reached the recommended 200 round break-in point. As of now, I have about 1200 rounds through my CM9, with NO feeding malfunctions whatsoever (after the mag fix). I tend to slingshot my slide, instead of using the slide release (as Kahr recommends). I have tried a variety of bullet types, HP, truncated cone, RN, etc, both cast and jacketed. Still no problems.

Anyway, not saying that your solution is in any way inferior to mine. Just another tack, that's all.

Oh, by the way, the problem with Kahr pistols breaking mag followers is easily solved. The reason this happens is that, in SOME examples, the mag follower makes direct contact with the bottom edge of the barrel feed ramp, when the slide is fully in battery. This can be solved by removing a small amount of material from either the front edge of the mag follower, or from the feed ramp. This problem does not occur with every example of the Kahr pistols, apparently only a minority of them. Nevertheless, as I said, it is easily solved.

As for your dismay regarding the fact that Kahr has apparently not caught on to (or accepted) the mag problem and the relatively simple solutions - I couldn't agree more. In fact, I posted my explanation and solution on the "Kahr Talk" forum some time ago....and you'd have thought that I insulted the mothers of (at least) some of them. They acted as if I was committing heresy, or treason, perhaps. Needless to say, I don't go back to that forum anymore.
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Old November 22, 2013, 06:14 AM   #3
dean1818
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I had Kahrs and ended up doing the follower modification which also seemed to solve this issue

This is a design flaw as well as the exposed slide release spring

Although, overall

The kahr is a nice lightweight, inexpensive CCW.

I never got used to the long trigger pull.

Sold the kahrs, never looked back
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Old November 23, 2013, 01:36 PM   #4
wpsdlrg
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I had the opposite experience with my Kahr (CM9). It is the most accurate pistol I have. Crazy accurate. Stupid accurate. Scary accurate.

The FIRST round, from the first magazine I ever fired from it, went dead center into my target, at 8 yards. That first magazine produced a group of about 1.5", at that distance. No need to get used to the trigger for me.

I routinely shoot the darn little thing at 25 yards now, off hand. I also routinely get 3.5 - 4" groups.....short sight radius, long trigger pull and all.

Go figure.

Still, I am not a Kahr fanboy. I bought the thing for a small carry piece, because I was tired of schlepping 2 lbs+ of pistol around everywhere. Can't say I "love" the Kahr....don't really like it as much as my other pistols....but, I cannot argue with the results.
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