Cracked Slide--Have You Seen this Before?

[Bongo Boy]

This is a used K40 that I've put maybe 1,000 rds through at most. The last 100-150 rds were just under max (Hodgdon published max, so fairly conservative).

http://i182.photobucket.com/albums/x150/Bongo_Boy/K40Slide.jpg

Wondering if anyone has experienced this. While I wait for sights to be installed on the new slide, I can tell you I certainly do miss the convenience and fashion versatility afforded me by this little gun.

Plan is to put a 1 lb heavier Wolff spring in it and then try to break it again. :rolleyes:

[gb6491]

First time I've seen that. It appears that the crack follows the rail.
Thanks for sharing the photo. I hope the new slide works out better for you.
Regards,
Greg

[kerby9mm]

What I don't know about metal could be an entire book. What would cause forged steel to crack?

[Longitude Zero]

WOW. Possibly a casting flaw in the original forging?

[LorenzoB]

They are machined from bar stock (not cast or forged). So a bad cast or forge couldn't be the problem.

I have machined bar stock before that had inclusions in the bar (some impurity or something that caused a shift in the molecules and prevented a proper crystalline structure when the bar was shaped at the steel mill). But this is extremely rare.

Do the slide rails look the same depth on both sides? If not, do you have another Kahr you can compare the machined depth of the slide rails? I'm thinking the metal was too thin there.

Or, you did say it was used. But you didn't say for what... maybe it was used as a pry bar? :D

[Bongo Boy]

Everything appears to be milled as intended, but the material is quite thin there, no doubt. What's odd, to me, is that no matter how heavy the round fired, I wouldn't expect much upward lift on the slide.

The problem in this area of the slot is that the slide lock recess is removed all the way across the slotted area. This means there's an abrupt end to the 'overhang' or lip, ending immediately below the 'R' in 'KAHR'...and obviously, that's where the crack started.

Unfortunately, this is the very same location where the matching rail on the frame begins, when the slide is in battery. In fact, when the slide is in battery, it is only engaged with the frame from the slide lock notch rearward--no part of the slide forward of the notch touches the rail on the frame.

To me, that means that the only time the slide sees an upward load that would cause the crack to propagate is exactly at the moment of discharge and until the slide has moved aft the width of the slide lock recess--about 7 mm--and that's where all the action occurs as far as impulse from the discharge, no?

Anyway, it's a deep, sharp-cornered slot that ends at the slde lock recess, and so it's no surprise at all that the crack would start there even with excellent materials. Any time a you take a sharp corner, stress goes through the roof--exactly the same reason you can snap a piece of glass by simply scoring it.

When you can make a part by only forging it, its ideal because you've taken the material and basically flowed it or 'rolled' it around corners to shape it. Even sharp contours still leave relatively smooth directional changes in the material's inner crystalline structure. As soon as you machine it, you slice right through that structure. It's not an issue, except where you then concentrate a load on a location that is not only a sharp corner but a machined sharp corner. That's bad juju.

One minor mod to the cutter that would make an immense improvement would be to knock the corners off of it, so the bottom of the slot has chamfered corners. Of course, then you'd have to knock down the corners of the matching rail on the slide, too. But, this would dramatically cut down stress concentration and reduce liklihood of a crack starting.

Other fixes would be to find a different way to engage the slide lock lever so you didn't need to have a cut right across the slotted area of the slide, or to extend the frame/dust cover forward 3/8" inch so the slide was engaged with the frame forward of the slide lock recess when the gun discharges.

I'm thinking I install a new slide, put in a heavier spring, and never load with Longshot again which I don't plan to do anyway. Easy.

[saltydog452]

delete.

[jocko]

bongo boy. you just got a defective slide. IMO don't try to figure out a fix for what is definitely a bad slide. It happens. Kahr will take care of it. I have never seen one like it ever. or has it ever been reported on this fourm.

I see nuttin wrong in the way the slide lock lever works. To my knownledge kthis has never been an issue on any kahr.
God knows how many million glocks are made like that let alone those butt ugly 1911's.. Just sayin

[Bongo Boy]

I understand what you're saying. I'm not too worried about it happening again. There really shouldn't be all that big a load on the rail anyway, as I see it.

The 1911 design isn't really the same--while it has a recess for the slide lock lever, that recess doesn't cut into or across the slot in slide, and doesn't leave an abrupt, sharp hanging load-bearing rail. It looks like the M&P slide is similar in this regard, though.

Kahr said I needed to just buy another one--which is what I expected them to say given I bought it used and it's 10 years old I think. I sure do miss this little gun. Right now it's in the shop waiting for a proper-fitting press for the front sight. Very frustrating.

And the 1911 is among the most beautiful handgun designs of all time, blasphemer! I believe we must reserve 'butt ugly' for Glocks, the Nambu and, okay, anything nickel plated. ;)

[Bongo Boy]

New slide is now fitted with the night sights, and life is good once again. I really like these sights over the ones on the original slide, as they seem somehow 'crisper' to me for whatever reason. In any case, my favorite 'around town' carry is back and I couldn't be happier. Blasted a few rounds downrange today and while groups are centering a bit to the right initially, by the time I got done they had opened up quite a bit and centered nicely. :)

http://i182.photobucket.com/albums/x150/Bongo_Boy/NewSlide02.jpg

[Cokeman]

What's the U on the trigger guard?

[jocko]

[QUOTE=Cokeman;199393]What's the U on the trigger guard?[/QUOT




A. If there is a "U" engraved on the trigger guard of your pistol, it is a factory refurbished and test fired model (often sold as a "test fired" gun). The gun is considered to be used, will come with one magazine, and is sold with a one year warranty.

[muggsy]

bongo boy. you just got a defective slide. IMO don't try to figure out a fix for what is definitely a bad slide. It happens. Kahr will take care of it. I have never seen one like it ever. or has it ever been reported on this fourm.

I see nuttin wrong in the way the slide lock lever works. To my knownledge kthis has never been an issue on any kahr.
God knows how many million glocks are made like that let alone those butt ugly 1911's.. Just sayin

Butt ugly 1911"s! Them's fightin words, Jocko! My wife says my cute butt was my best asset, so to speak. :)

[Cokeman]

Oh. OK.

[CJB]

Butt ugly 1911"s! Them's fightin words, Jocko! My wife says my cute butt was my best asset, so to speak. :)

So, how long as your wife needed stronger glasses?