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Czechmate barrel failed


gianmarko

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Hi all

last saturday the barrel of my CM failed during a competition.

the barrel has less than 5000 rounds and mostly used with relatively low PF

i was very surprised to see such failure. actually i had just installed this relatively low usage barrel for the competition, as i was flying airline with a weapon and i didnt want to bring a spare barrel with me and risk troubles with the airport security

not sure where to post this, any comment is welcome

is this perhaps the reason why the CM comes with 3 barrels? i really hope not...

the gun limped through the stage but i had many FTF and FTE

i anyway arrived third in my category, 4th overall with a borrowed CM (and that CM owner also had a barrel failing in the same way...)

bb1.JPG

Edited by gianmarko
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Yes, that is common, and does indeed seem to be why they include extra barrels. I think a stronger recoil spring helps them last longer.

ouch. not really what i hoped to hear :D

ill look for stronger springs.

for the rest, great gun and i love it. might get a second one when i have the $$$

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What weight springs are you using for recoil and hammer springs?

I think the hammer spring/firing pin stop angle might have more to do with the break in the picture.

I'm just starting to experiment with firing pin stop angles, but I think the 2011 guys are way ahead of us in that department.

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In addition to the spring weights, I'm curious what load was used for the bulk of shooting? With or without the comp?

ETA: It looks like they beefed up the radius a little on the backside of the stop in later production. This picture is from my spare barrel, which I've had for about a month.

post-59794-0-77216300-1450220519_thumb.j

Edited by busdriver02
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What weight springs are you using for recoil and hammer springs?

I think the hammer spring/firing pin stop angle might have more to do with the break in the picture.

I'm just starting to experiment with firing pin stop angles, but I think the 2011 guys are way ahead of us in that department.

Had the my TS 40's barrel break there, but round count was 15-19 K. Could you explain how the angle you mentioned would cause the barrel lug to crack, please.

Thanks,

Steve

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It looks like the source of the break was the slide stop pin pounding the front of the "peanut" this happens early in the recoil cycle and is what pulls the barrel down to unlock the upper lugs from the slide. This happens within the first 7mm of slide movement at which point the firing pin stop is beginning to cock the hammer spring with very little leverage, so if you wanted to slow down this first little bit of slide movement the recoil spring would have much less influence than the hammer spring. Like I said, I'm just starting to visualize the importance of the firing pin stop and hammer spring weight in the recoil cycle, so I'm not ready to make definitive claims, just thinking out loud :wacko:

It seems like a heavier hammer spring would help, but with the same firing pin stop angle it would create more muzzle flip. If you change the angle so that it contacts the hammer higher up giving it more leverage on the spring you could maintain a higher force for longer. Real world testing to follow... :eatdrink:

Edited by kneelingatlas
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kneelingatlas, I went through those same mental mashing exercises a couple months back. Here's what I came up with:

-Regardless of FPS shape, the work done by the slide on the mainspring is the same since it compresses the same distance regardless; levers don't change the amount of work done.

-What changes with FPS shape is the time that it takes to cock the hammer; work/time is power.

If I'm reading your words right, you're thinking increase mainspring weight then round off FPS more to offset the spring change. If anything, I would think you'd want to go the opposite direction. My thought is move as much of the work done on the mainspring to before the barrel hits the slide stop.

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-Regardless of FPS shape, the work done by the slide on the mainspring is the same since it compresses the same distance regardless; levers don't change the amount of work done.

Over the entire slide stroke yes, but we only want to concern ourselves with the first 7mm of movement before the front of the peanut crashes into the slide stop pin. Don't forget your wrists are doing work at the same time.

You might be right that a square bottom firing pin stop would do the best job of protecting the lower lug, but I think it would do so at the cost of more muzzle flip.

I guess I'm mixing my desire to reduce muzzle flip with gianmarko's wish to protect the lower lug of the barrel. To that end I think reducing the weight of the comp could reduce the stress on that area.

Edited by kneelingatlas
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You might be right that a square bottom firing pin stop would do the best job of protecting the lower lug, but I think it would do so at the cost of more muzzle flip.

I guess I'm mixing my desire to reduce muzzle flip with gianmarko's wish to protect the lower lug of the barrel. To that end I think reducing the weight of the comp could reduce the stress on that area.

I agree reducing comp weight would help. I was thinking flat bottom stop and lighter mainspring. That way you'd keep the power "the same" for muzzle flip considerations, and move more of that work to an earlier point in the slide travel so it'd help with the barrel wear.

Edit: I just whacked out a flat bottom stop from an extra 1911 piece laying in my parts bin. It's not a huge difference, the stock part's contact point on the hammer is already pretty low.

Edited by busdriver02
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Have any visual references on this Atlas? Trying to wrap my hear around it.

The hammer acts a bit like a really weak lever delayed block back mechanism. (Link) The red block in that picture is a heavy weight. In this case, we have the hammer spring. That spring is nothing compared to the recoil force, but the hammer does push on the back of the slide in battery and resist unlocking a little bit. A heavier spring pushes a little bit harder/ resists unlocking a little bit more and slows the slide down a bit. This can make the gun feel softer, and if you're shooting bullseye might make the gun ever so slightly more accurate.

How much it affects slide velocity is a function of force x distance, in this case the distance the spring compresses. However, any resistance to unlocking will cause the muzzle to rise a bit. In an iron sighted gun it probably isn't noticeable, but with a dot it's different.

A flat bottom stop pushes on the hammer lower and a rounded stop pushes higher. Imagine those two contact points on the hammer and the arc they would scribe if you could use the hammer like a compass. The flat stop/lower contact point would scribe a smaller diameter circle. Let's assume the hammer gets cocked over 90 degrees of travel, it's not but it works for a visual. That means in my example the distance the slide has to travel to cock the hammer is equal to the radius of that circle. The key thing is the slide velocity is the same at the start of the cocking regardless of stop shape, so the flat bottom stop will cock the hammer faster. Since it's doing the same work (spring compression) over a shorter period of time it will slow the slide more. Work over time is the same equation that gets you horsepower in your car (in that case torque over rpm). It's also a slightly stronger lever delay (really tiny difference here, remember the recoil dwarfs the force difference).

My thought is that by dropping the firing pin stop edge and lightening the hammer spring (assuming you still get reliable ignition) you'd have the same overall power and muzzle rise. But since the hammer starts cocking as soon as the slide starts back, you'd move more of the hammer spring compression cycle into the part of slide travel before the barrel drops out of the slide.

The pain in the butt part is that a flat bottom stop isn't enough, you really need the hammer to sit flush with the stop when the hammer is down. If the hammer is touching the stop only up near the firing pin, that's the leverage point when the cocking cycle starts, not the bottom.

I don't know if that actually helps. I'm also not sure it's really 100% correct. I tried to actually model this mess a couple months ago and gave up when I realized I'd need to do a bunch of math I forgot how to do.

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What weight springs are you using for recoil and hammer springs?

I think the hammer spring/firing pin stop angle might have more to do with the break in the picture.

I'm just starting to experiment with firing pin stop angles, but I think the 2011 guys are way ahead of us in that department.

i am using the stock springs that came with the gun. not sure about the weight, i did some research some time ago but nobody could give me an answer

i have bought two recoil springs from CZ at the last EEO but havent even unwrapped them yet, and not 100% sure they are specific CM springs or just standard TS springs, the guy at the shop spoke very poor english

i am sort of aware that there is a weakness in that area in the browning-petter locking system but i was very surprised to see the barrel fail as it not used much, it was originally the barrel coming in the gun (it is shinier than the others and have a B serial number as the gun) and at some stage last year i replaced with one of the spare barrells. the spare barrel i had on has a lot more rounds through it.

the spare barrels have a A serial number and a /1 and /2

wonder if A and B serial barrels are in any way different, apart that the A ones are not polished.

very interesting discussion about springs.

a harder main spring would increase the trigger weight, i assume?

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here you can see the different look of the barrel originally in the gun and the spare one

http://gianmarco.dyndns.org/brokenbarrel/IMG_0033.JPG

http://gianmarco.dyndns.org/brokenbarrel/IMG_0050.JPG

different material or just polished? i cant tell

here you can see that the slide lock does not seem to contact at all the front of the cam at the end of the recoil cycle

http://gianmarco.dyndns.org/brokenbarrel/IMG_0039.JPG

http://gianmarco.dyndns.org/brokenbarrel/IMG_0036.JPG

http://gianmarco.dyndns.org/brokenbarrel/IMG_0037.JPG

http://gianmarco.dyndns.org/brokenbarrel/IMG_0034.JPG

http://gianmarco.dyndns.org/brokenbarrel/IMG_0035.JPG

here you can see that the contact area between cam and slide stop is different in the two barrels

result of shooting with a broken cam? dont know

http://gianmarco.dyndns.org/brokenbarrel/IMG_0055.JPG

http://gianmarco.dyndns.org/brokenbarrel/IMG_0056.JPG

i guess the ramp hits something at the end of the cycle if the cam is broken

http://gianmarco.dyndns.org/brokenbarrel/IMG_0057.JPG

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i have checked the replacement springs i have, the wire is 1.1mm while the original spring is 1.0mm, same as the original spring of my shadow.

don

i have installed that, will test it soon

1mm = 0.0394" and 1.1mm = 0.0433"

Here are the spring diameters I measured on my CZ recoil springs:

10# - 0.0385"

11# - 0.0390"

12# - 0.0400"

13# - 0.0405"

14# - 0.0415"

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KA, on a 1911 (45ACP) a smaller radius on the firing pin stop slightly increases the cycle time because there is less mechanical advantage to cock the hammer. The effect on felt recoil is significant. It is reduced, as is muzzle flip. The only down side is manually cycling the slide is a lot harder. Little changes make big differences. Using a square stop, it is really, really hard to rack the slide, but the recoil/flip reduction is significant. A 1/16" radius makes a world of difference, but you still have to grip the rear serrations hard. Moving to a 3/32" radius makes things easier, but you give up more of the felt recoil reduction. Anything past 3/32" and you might as well stay with the humongous radius the put on standard stops.

The radius on the factory stop on my TS is significantly larger than what I use on my 1911s.

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I have had the exact same issue with my two Czechmates. They break the barrel in the exact same spot. I have relayed this information to CZ and they are aware of the issue. They do have a new barrel design with more meat in that area where the barrels are breaking. I just received those barrels and will have them fitted by a gunsmith. Hopefully that helps the issue. The gun still breaks slide stops which great frequency so it is obvious that there is a lot of energy being placed on that area. It also appears that the slide stops have uneven wear on them so they are being loaded up on smaller points instead of the energy being spread across a larger area.

I am no engineer, but it is obvious that a solution is needed to lessen the impact to the slide stop and barrel peanut. I thought maybe a heavier hammer spring would help but I have no idea how much of that comes into effect during the part of recoil that loads up the front of the peanut.

Edited by flgcwpg
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.

I guess I'm mixing my desire to reduce muzzle flip with gianmarko's wish to protect the lower lug of the barrel. To that end I think reducing the weight of the comp could reduce the stress on that area.

I have an extra comp and was thinking the same thing. A lighter comp would mean less energy being transferred right? Of course, less weight off the end of the barrel means more flip as well. Suggestions?

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I'm a big fan of light comps; Limited guns use weight to reduce muzzle flip, but Open guns can use comps and ports to do that.

IMG_20150103_134803992_zpsczbv9lha.jpg

I opened up the first port of the comp a little (a fantastic mod by the way, I highly reccomend it), so the factory comp may weigh a hair more than this one, but I think if you hack the bottom off it, and put some ball cuts in the sides and bottom, you might shave an ounce off it, which would make it feel significantly lighter in the transitions. I also recommend using a plastic guide rod instead of a steel one to lose another ounce out of the nose. My next CZ open gun will use a custom comp made from either Ti or Aluminum.

19207_zpssue0b7pu.jpg

Edited by kneelingatlas
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i have emailed CZ but still no answer...

KA, wont the compensator unscrew itself from the barrell without the guide part?

regarding my barrels, the spare barrel i have used in the last year and half shows no sign of wear or contact in the front of the cam, i suspect that could be a factor. also slide stops do not show any sign of wear, just the black surface treatment wears out somewhat.

the original slide stop with the hold open did not last long, the spare slide stop without hold open that came with the gun is still ok after at least 10k rounds.

of course now i need more details about the 1st port mod :-)

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You would need to use thread locker to keep the comp on although I'm working on mods to permanently fix the comp to the barrel and pull it out the front like a Tanfoglio.

I don't have a good picture of my CZ comp handy, but this Tanfoglio picture shows it well between the stock three port in the center and modified one on the left. Since the first port does the bulk of the work I've found slightly enlarging to helps the effectiveness of the comp.

Tanfo%20Comps_zpsoytnv5ko.jpg

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