leadchucker
New member
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?
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?