CW9 problem and the polymer myth

[zenigata]

My CW9 developed a problem where it would fail to return to battery. It would stop about 1/16" shy. Took a while to figure out what the problem was, in part because of that claim by Kahr that the slide only rides on the metal inserts and not the polymer.

Turns out that's not true, at least on the CW9. There is a gap milled in the right rear corner of the slide. When the slide is moved back about 1/16" the insert is in that gap. At that point the insert is not holding the slide. The only thing keeping the pressure from a full mag pushing that corner of the slide up is the polymer rail.

After a large number of rounds (less if your slide was as rough as mine) the poly rail will wear enough to allow the slide to rise when this gap passes and the metal insert gets caught in the gap. That's what is happening with mine. You can actually see the gap between the frame and slide get wider at that point.

I sent this back to Kahr to have it repaired. They replaced the spring, the slide, and the barrel, but didn't fix this. Still does the same thing. The only difference was that I had to fire a number of rounds through it before it started doing it again.

They refuse to acknowledge that this problem exists. They either really believe that "The slide does not ride on the polymer rails at all during cycling, only on the metal inserts both front and rear" or they are deliberately denying a known design flaw for fear of liability. Why they mill all the way into the slide rail slot I can't imagine.

Please don't take it that I'm some kind of Kahr hater. I love my little gun and I will be getting it fixed one way or another. If not, I may pick up a K9 to replace it.

[Mike_B]

Can't go wrong with a K9- the NYPD trade ins only cost a little more than a CW9. IMO you should get one while they're still available......Or if $$ isn't an issue, just buy a new one!

As to the slide issue, can't comment on that. There are a lot of knowledgeable people on here qualified to discuss it though.....

[gb6491]

Zenigata,
Welcome to the forums.
I think you bring up a valid point about the metal frame inserts. I wouldn't go as far as to call it a design flaw because of the failure of one particular pistol (yours is the first I've ever heard or read of having an issue because of this) or even to agree with your statement that "After a large number of rounds (less if your slide was as rough as mine) the poly rail will wear enough to allow the slide to rise when this gap passes and the metal insert gets caught in the gap." (that's supposition unless you've tested a large number of pistols and they did actually fail the same way), but, as your pistol has developed an issue, I do agree there is a chance other pistols could do like wise (especially out of spec guns). However, given the large number of poly Kahrs out there and the low (01) reported incidences of this happening (admittedly just on this board and a few others), I'd guess that in properly spec'd guns, the other three metal inserts are providing enough support/guide/bearing surface that the small amount of time the right rear rail is in the disconnector window has negligible effect/affect on the pistol (to include wear issues).
Now with that said, I surely wouldn't mind seeing the metal rail insert made longer on that side of the frame so that it extends forward past the disconnector (BTW, that cut in the slide rail is there to accommodate the disconnector). Then again, I'd also like to see a metal insert or backing plate for the slide stop spring screw.
Please keep us up to date on getting your pistol back on line.
Regards,
Greg

[jocko]

the slide actualy does not ride on the polymer rails,, there is no strenght in poly rails for slide action in a semi. I can't think of one gun that rides on polymer rails,The back rails on the poly kahrs is what actually takes the brunt of the slide action and I have yet to see a worn out back rail or broken one even. Could it be longer as GB stated?? Probably so,, but darn kahr must have 200K of those poly guns out there and to my knowledge no issues with the about 1/2"" long back rails. They must indeed be long enought to keep the slide in perfect alighnment along with the front rails also being a guide to.... now like GB stated if the polymer rails are out of spec for some reason the slide will make contact but it is not by design. Normaly slide action wears these high spots down and all is well. the polymer rails are there to #1 strenghten the upper frame . #2 serves as a guide to properly reinstall the slide back on the frame. Those rails u could cut off with a knife and the gun will suffer no ill effects.

Zenigate, sorry I disaree with ur analysis,

[gb6491]

Speaking of my CW45 and CW9:
Zenigata is correct in that for a small portion of the slide's travel it is not completely "captive" of the right rear, metal frame rail. To allow for function of the disconnector, the slide is machined in a way that a bottom portion of the right rail is missing near the rear of the slide. The slide may be "riding" on top of the frame rail when the open bottom portion passes by that rail, but it's not "captive" on that corner when it happens. Given the correct set of circumstances (possibly a gun that is out of spec in how the other rails fit) I find it conceivable that some vertical play could occur during that brief period when the open, bottom portion of the slide rail passes under the rear frame rail insert.
http://i45.tinypic.com/2uy3tci.jpg
Regards,
Greg

[kerby9mm]

I have no desire to own a poly gun of any make. I realize they are for weight reduction especially in high round capacity guns for the consumer. For the manufacturer they are cheap to make. Plastic injected into a mold to save on weight or enhance profits. Titaniun or some other alloy that has to be machined costs more so the price of the gun would be higher to probably make less profit and not sell as many. What do companies choose nowadays?

[jocko]

I have no desire to own a poly gun of any make. I realize they are for weight reduction especially in high round capacity guns for the consumer. For the manufacturer they are cheap to make. Plastic injected into a mold to save on weight or enhance profits. Titaniun or some other alloy that has to be machined costs more so the price of the gun would be higher to probably make less profit and not sell as many. What do companies choose nowadays?

why kahr and some other makers still makie steel guns for guys like u that demand them. No doubt polymer is lowe rn price to make, but over all it is the extreme weight reduction that draws shooters to the gun. My Poly P9 shows zero wear anywhere, not a mark on my poolymer rails. Glocks have endured for years.Maybe someday there willbe a metal as light as polymer and affordable to make and machine and we will then see the rebirth ofthe steel guns. Wouldnot be a bad thing, for I amsure if a 14ounce PM9 polymer gun and a 14 ounce steel PM9 were i the showcase and priced the same the polymer would be sitting there a very long time. Who knows witrh todays technology and new materials, it could happen sooner than later to.

How many here have MK series kahrs and state that although it is a super gun, it is heavy fr pocket carry, where as the PM/cm kahrs seem to do just well there.

There will always be steel guns but i the lat half dozen years polymer models intordcutions far out number any steel introduction guns, except the 1911's still maintain their all steel over polymer and I think tha tis also becuase the shooting public wants the 1911's in stell over polymer. I love my K9, it is one hellof an atrtractive gun IMO, just not pocketable.

[jocko]

Speaking of my CW45 and CW9:
Zenigata is correct in that for a small portion of the slide's travel it is not completely "captive" of the right rear, metal frame rail. To allow for function of the disconnector, the slide is machined in a way that a bottom portion of the right rail is missing near the rear of the slide. The slide may be "riding" on top of the frame rail when the open bottom portion passes by that rail, but it's not "captive" on that corner when it happens. Given the correct set of circumstances (possibly a gun that is out of spec in how the other rails fit) I find it conceivable that some vertical play could occur during that brief period when the open, bottom portion of the slide rail passes under the rear frame rail insert.
http://i45.tinypic.com/2uy3tci.jpg
Regards,
Greg

have a point although IMO with the 3 steel rails that is guiding the slide backwards, my opinion is that the polymer rail on the right side bears no force and could actualy be cut away with no loss of reliability. captive it is not. Not arguing, just giving my opinion.:D

[OldLincoln]

That must be another difference in the PM9. My PM9 doesn't ride on that part of the slide. It rides on the inset part just above those orange points in the pic, not the bottom of the frame sides. Thus, my rear supports never leave the slide.

[gb6491]

That must be another difference in the PM9. My PM9 doesn't ride on that part of the slide. It rides on the inset part just above those orange points in the pic, not the bottom of the frame sides. Thus, my rear supports never leave the slide.
Old Lincoln,
My apologies for not being clear in my previous post. The slides of my CW45 and CW9 do ride where you describe. Here's the photo again with a facsimile of the rear metal frame rail superimposed at several different positions along the slide rail. In two of the positions (A&C) the frame rail is captive between the top and bottom of the slide's rail (this limits vertical movement of the slide). In the other position (B) or any point between the two arrows, the metal frame rail has nothing below it to limit upward movement of the slide. As I said before, I don't think this would cause a problem in a properly spec'd/undamaged gun, but I can see where it could do so in an out of spec/damaged gun.
http://i50.tinypic.com/2503y9x.jpg
Regards,
Greg

[espresso]

Are you sending it back to Kahr again?
How many rounds do you have through the gun and how old is it?

I'd love to know how Kahr or a gunsmith fixes your gun

[jocko]

I would guess if anything on a gun is out of spec, one should consider issues: Just sayin. Lots of if's IMO.

[espresso]

Yeah I hear you jocko. I've hung around here a good bit and this is the first report of it.
I'm curious to find out what is out of spec and how it gets fixed.
New frame?

[jocko]

Kahr if they replace anything is not gonna tell anyone what was what. we can assume, if that makes one happy. Bottom line is for khahr to get it right. GB is not off on harldy any of his comments but I just don't buy this, except if the slide is out of spec, . then we are talking apples and oranges. If it is in spec , that area is a mute point IMO. as u still have 3 steel rails keeping that slide in perfect alignment,,,for that millioneth of a second. But again that is my opinion to and u know about opinions. In my years of being on this forum, this has never been an issue that we can document either.
We have seen slides replaced on kahrs, so do we assume what? Just sayin

[Scoundrel]

I can't think of one gun that rides on polymer rails

I can't verify it right now because it is no longer in my possession, but I am 90% certain that the Ruger P95 does not have any metal on its polymer rails.

[jocko]

no ur right the Ruger P95, 97 and 345 road on very big polymer rails and to my knowledge they never had any complaints from them, but saying that the Ruger slide polymer rails were slot stiffer due the design of it carrying the brunt of the slide. Kahrs rails were never made to ride the slide for function, but Scoundrel. I stand corrected.

[Scoundrel]

no ur right the Ruger P95, 97 and 345 road on very big polymer rails and to my knowledge they never had any complaints from them, but saying that the Ruger slide polymer rails were slot stiffer due the design of it carrying the brunt of the slide. Kahrs rails were never made to ride the slide for function, but Scoundrel. I stand corrected.

The Ruger's also a much bigger pistol. More material there to make it stronger to withstand the stresses. Can't do that with a mouse gun.

But anyway, back to the subject at hand...

[zenigata]

Thanks GB for your help with excellent explanation and photos. I sent multiple photos to Kahr prior to returning it to them They either failed or refused to understand what you obviously grasp.

As for sending it back to Kahr again, I don't believe they are interested in resolving the problem. According to them "You can completely cut the polymer rails off of your frame and the gun will still function". Of course this is not true. The upward force of the top round in the magazine would push the right rear corner of the slide upward and out of position.

It might work with no mag inserted (mine does), and then maybe the weight of the slide would allow it to ride on top of insert. But I would hardly call that functioning.

As far as the number of rounds, I'd say less that 10K, but the edges of my slide were so sharp I had cut myself on them while cleaning the gun.