What could cause a barrel to crack across?

[BoyGlock]

This is a CZ SP01 barrel about 20k rounds old of IPSC minor loads

[elguapo]

It could be many things, but one thing is for sure, corners on machined parts are stress risers. Inside corners, like the blend at the base of the front locking lug to the barrel OD, can be radiused to reduce the stress concentration. However, that technique can fail if the radius is too small, the barrel is too brittle (incorrect heat treatment), there is an inclusion or internal flaw in the steel near the stress riser, and a few more things that I am not thinking of at the moment.

Bottom line, without sending that barrel to a competent metallurgical forensics lab, it's speculation. Throw it away and buy a new one.

[scottlep]

I am certainly not a metallurgist or gunsmith, just my 2 cents. The discoloration and possible grinding/finishing marks in that area are intriguing. It looks as thought that area around the lugs might have either been repaired before, or the area was heated when being cut or finished which could have weakened the lug area?

[P.E. Kelley]

I am certainly not a metallurgist or gunsmith, just my 2 cents. The discoloration and possible grinding/finishing marks in that area are intriguing. It looks as thought that area around the lugs might have either been repaired before, or the area was heated when being cut or finished which could have weakened the lug area?

I have the same thoughts...Looks like it has been heated at some point (well beyond what one could do shooting it)

[rdinga]

I wonder of a trend of high volume shooting sessions using titegroup could induce that much heat to the area?

[BoyGlock]

I am certainly not a metallurgist or gunsmith, just my 2 cents. The discoloration and possible grinding/finishing marks in that area are intriguing. It looks as thought that area around the lugs might have either been repaired before, or the area was heated when being cut or finished which could have weakened the lug area?

The local discoloration was the result of purposely removing the gun blue with a spirit so the crack would be visible in the camera.

[Miranda]

To be careful, knowing what caused the crack is expensive.

and my end up being a guess even after a careful analysis.

speculation and support for that guess is less expensive.

and far less certain.

such cracks can be from thermal cycling, mechanical loading and manufacturing flaws

such as no radius on the lug and metal composition.

the fix is the same... replace the part.

your choice of replacement may be informed by the reason the part broke.

look for a radiused lug and powder that does not get as hot.

miranda

[elguapo]

That discoloration is not what overheating looks like, much less an amateur attempt at hardening.

[Whoops!]

I'm guessing 20k round is an approximate round count. These barrels are rated to 30k rounds, and many of them do crack after that amount. I imagine you may not be too terribly far off.

I wouldn't worry about it.

[BoyGlock]

The pistol is unusable now after discovering the crack and that it penetraded down the rifled bore inside. Is there an aftermarket barrel available? Its located outside USA. Otoh IPSC production div. does not allow aftermarket barrels.

[elguapo]

Here's a thought........call your country's CZ importer or distributor and ask if you can buy a factory replacement barrel.

Here in the US, CZ-USA will sell you a barrel (or any other part besides the frame) through their website store.

Edited October 25, 2014 by elguapo

[RussellM]

That barrel looks like hell. I have 2 Shadows with 30k plus through each and the barrels look about like they did when they were new. It looks like sanding marks down towards the muzzle end.

[BoyGlock]

Thanks for your input everyone. Im more inclined to the barrel being unaltered so Im looking for possible cause outside of that.

Eta. The gun is not mine so what do I know?

Edited November 1, 2014 by BoyGlock

[Miranda]

mmmmmm.

where the crack is on the part is easy.

the lugs kept the crack from being under lugs,

or the lug causes addition support.

there are a lot of ways to say that.

the reason there is ANY crack at all... is much harder.

the heat from firing causes heat cycling, which can cause cracking

in most metals.

the pressure cycling from firing can cause fatigue fracturing...

a single over pressure event can cause fracturing also.

( this can be from un-noticed up to spectacular...)

the solution is mostly the same...

replace the part.

[BoyGlock]

Thank you sir.

Im really baffled by the nature of this failure. Its very unusual. Aside from learning from it and avoiding its possible causes in the future, it could shed some light to forces acting in a pistol unknown to me.

[Vlad]

I'd assume if the locking lugs are not perfectly fit to the slide (and when are they ever), and if the slide can move backwards enough to build up some velocity before hitting the first lug, that could end up cracking the barrel after a while, specially if there is a stress riser there.

[elguapo]

I'd assume if the locking lugs are not perfectly fit to the slide (and when are they ever), and if the slide can move backwards enough to build up some velocity before hitting the first lug, that could end up cracking the barrel after a while, specially if there is a stress riser there.

That would be my guess also.

[elguapo]

Thank you sir.

Im really baffled by the nature of this failure. Its very unusual. Aside from learning from it and avoiding its possible causes in the future, it could shed some light to forces acting in a pistol unknown to me.

It is very unusual in that it doesn't happen very often. However, the failure mode (crack starting in a corner) is very common in machines of all kinds.

There is absolutely nothing you, as the end user, can do to prevent something like this from happening.

The best you could do, if the same failure worries you so much, is to find the onset of a crack as early as possible by having the barrel checked using the magnetic particle inspection method and/or industrial radiography at regular intervals.

However, doing so is overkill in terms of time and money for something that is statistically a non issue.

In other words, I would not sleep over this problem. If you ever see it again, throw the barrel away and replace it with a new one.

Edited November 3, 2014 by elguapo

[Miranda]

Hi Vlad,

'stress riser' is exactly why the crack is there.

I was avoiding using the term because I have found

I had to explain it when ever I used it.

I also do not know how the lugs are used in relation to

the barrel. it is easy to understand the crack

if the slide stops on that lug.

miranda

[elguapo]

I also do not know how the lugs are used in relation to

the barrel.

The lugs lock the barrel into recesses milled in the underside of the slide when the slide goes into battery.

[Vlad]

I also do not know how the lugs are used in relation to

the barrel.

The lugs lock the barrel into recesses milled in the underside of the slide when the slide goes into battery.

Yep, but it is the hood and the funny little bump on it that control its forward position, so the lugs may not fit perfectly in the slide and still get solid lockup at rest. I suspect there is a gap forward of the lugs and as the slide starts to move backwards and the barrel unlocks the slide smacks into the front lug.

Thats my guess anyway.

[BoyGlock]

If the slide hits the lug rearward it should shear the lugs. But the crack across suggests that a force is stressing the barrel crosswise as if bending it downward. Could be barrel-slide fitting problem but where and how?

[Miranda]

is that part expensive?

when you have machinery in motion...

you have a stack of possibilities

at speed, the slide can hammer the lug

(the lug can hammer the slide...)

what happens is a lot like what you see when

you drop jello onto jello. lots of vibrations.

I have read that the right vibration can crack any thing.

I fully admit I am guessing from here.

I would look for anything that clips snags or tags

between the lug and the slide.

under fire, the extractor may pull the barrel into a different position

where the slide and lug can hit...

things like that are hard to test.

miranda

[BoyGlock]

If its due to "normal wear and tear" of the pistol there could be something very wrong in materials used or design. Expensive or not, a failure in a barrel like this cannot be sneezed at. I can tolerate failures w/ normal usage on springs, pins, etc. but not on major parts like barrel, slide and frame without obvious reason. Prolonged usage should not be reason enough for these types of guns in this type of failure. Just my opinion.

[daves_not_here]

What kind of springs are you using and how does your slide release look?

Also, are you seeing any wear on the inside of the slide or front bushing?

Unless it's just fatigue, bad material or bad heat treat there might be something out of tolerance causing stresses. Sharp corners focus bending stresses.

DNH