Bolt Lug Broken Off

[TJNewton]

From the first image, the metal looks porous; reminds me of pig metal.

Went back and looked and didn't realize you could zoom...  I don't believe these bolts are pot metal.

TJ -- did you lose material in the groove for the ejector or just off that lug?  Looks rather dark down that central channel as if some material was lost there as well, but hard to tell due to pic quality...  Now I know that some of the later gen VZ2008s have rails that fit a little low.  On there return to battery there shouldn't be any major ejector to bolt interference, but recoiling out of battery, the bolt could possibly have snagged on the extractor enough times to cause damage if there was inadequate clearance there, and the bolts can tilt/move slightly as well due to combloc tolerances on these rifles... 

Worth investing at least.  And as I look at the zoomed in pic, metal being torn out of that center groove and diagonal out towards that lug (looks to fragment further back on channel than lug) would be a plausible scenario.

Admittedly those pics aren't the best.  I looked in the ejector groove of the broken bolt and there's no unusual wear in that channel.  The break is clean, doesn't involve the channel, and the broken lug fits back without any (visible) gaps.  The ejector in the rifle is rounded and shiny on that side, but there are numerous shiny parts where the bolt and receiver interact, the wear being similar to my other VZ20008's.  I put the broken bolt into the receiver and while there is some lateral wiggle, it traveled smoothly and there was no palpable interference with the ejector while being moved back and forth under just light finger pressure.

Lateral movement isn't the concern.  It's the degree to which vertical movement of the bolt is possible. Hypothetically, if the internal rails are too low and top right at right height, that would allow for more vertical tilt.  I'll need to make some time to visually inspect to confirm, but hypothetically and given enough vertical travel, the bolt could tilt towards rear on recoil (not unlike AR carrier tilt) whereby the front of the bolt lifts up, forcing rear down, and continuing to the rear, the near front of the bolt impacts the ejector in a fashion that begins a fracture within the metal.  Then repeated enough times, it breaks. 

To test, try lifting the front of your bolt up 1/4" or so when testing and see if clearance w/ the ejector changes.  Lift up the rear 1/4" as well and try.  And to be clear, where the impact occurs could be part of a wave like motion whereby the front comes up and then the rear does before the bolt settles down.  Unfortunately, I don't have a high speed camera or a way to ensure entirety of bolt movement is visual.

As far as orientation, I'll be referring to the parts as though looking down the firearm from the rear sight to the front, e.g., the charging handle being on the right, the mag release on the left.

RSR -- I tried what you recommended on both my VZ2008's.  I also interchanged the bolts the between the two for experimentation.  I used the replacement bolt as of course the broken one doesn't have the lug that would catch on anything.  With both bolts and rifles, in both combos, the bolt, when pushed forward completely flat, does have minimal contact with the first ledge of the receiver that holds the ejector.  The contact is very, very light; a barely noticeable tick.  It takes no pressure to overcome it and is merely feedback.  With all combos of bolts and rifle, if the rear of the bolt is lifted even a millimeter, the front lugs will not clear that first ledge.  Continuing forward with the rear of the bolt lifted, the wider, right-side lug will be stopped by the circular recess that houses the mag release/bolt release split pin.  No amount of pressure will over come those two obstacles.  It seems that in order to lift the rear of the bolt 1/4", the rails would have to be equally higher -- an amount that I don't think exists in any VZ58 variation.  The carriers do have some scant up and down play in the receivers (about 1/100th of an inch), but I don't see any opportunities for the bolt to tilt either forward or back during actual cycling or firing.  The flat travel of the carrier in the rails would prevent that.

RSR, are you able to lift the rear of the bolts on your VZ2008's even the slightest and clear two the obstacles mentioned? Anyone else able to?

What I find curious is that while the top and both upper sides of the ejector are shiny and marked by contact with the two lugs, and the floor of the receiver to the right of the ejector that contacts the wider, right-side lug has a shiny strip of wear from front to back, there is zero wear on the receiver to the left of the ejector, the area that should contact the lug that broke.  Those marks are consistent in nearly all pics I've seen of VZ2008's.  While all variants of VZ58's have the bilateral gouges along the receiver to some extent, that singular strip to the right of the ejector seems to occur only with VZ2008's.  Below is a picture:

https://imgur.com/a/Ky5G3

The only contact the broken, left-side lug seemed to be making was with the left-top of the ejector, which based on other pics is normal.  No contact with the receiver, unlike the wider, right-side lug.

The Go gauge is on the way and I'll be doing some swapping around to see what effect the locking piece has on head spacing.

[RSR]

Offhand, my B&R machine VZ2008 from Centerfire does not (or does to a much lesser degree -- my first VZ58/variant, I lubed it well and have kept it fairly wet internally so minimal shine), but later gen VZ08PMs (or whatever the serial is) from Palmetto and AIM do exhibit this behavior.  I think it was ForcedMarch (or maybe CitizenPete?) who did a write-up on modding your bolt and ejector for adequate clearance due to the low rails on these receivers. 

[TJNewton]

Offhand, my B&R machine VZ2008 from Centerfire does not (or does to a much lesser degree -- my first VZ58/variant, I lubed it well and have kept it fairly wet internally so minimal shine), but later gen VZ08PMs (or whatever the serial is) from Palmetto and AIM do exhibit this behavior.  I think it was ForcedMarch (or maybe CitizenPete?) who did a write-up on modding your bolt and ejector for adequate clearance due to the low rails on these receivers.

Those are good write ups and I'll refer back to them.

Are you able to tilt your bolts as suggested and still able to clear the receiver and split pin recess?

[TJNewton]

The SAAMI Go gauge arrived today and I went to work.  Of my three VZ2008's, two closed on the SAAMI gauge, but one would not.  That rifle has 1200 rounds on it and I haven't noticed anything out of the ordinary.  The cases on random inspections have always looked fine.  On one of the two rifles that would close on the SAAMI, one was an easy, loose close, and one was tight.  None of them closed on a No-Go. 

I found that CIP gauges were much more forgiving and everything closed on the CIP Go gauges with much less pressure, some with no resistance at all.  None of them closed on CIP No-Go.  Back in 2014 I verified with Century that their VZ2008's are made to SAAMI specs, but either their chambers are extremely tight, or they are instead actually made to CIP specs.  Since the production of the barrels was farmed out, it's possible that the Century tech at the time didn't have the correct information, or that maybe some batches were SAAMI, and some CIP.

Then I went about switching around carriers, bolts, and locking pieces among the three rifles.  Every single item, as well as the barrel itself, has a huge effect on head spacing.  Different combinations of the pieces will yield completely different results.  I have six total locking bolts, and they varied widely in tightness.  I have four carriers and they also greatly affected head spacing.  One combination of carrier, bolt, and locking piece was so loose that it caused the action to close on the CIP No-Go gauge, although it was still fine with a CIP Field gauge.  Some combinations were so tight that they would not even come close to closing on a SAAMI Go gauge and were very tight on the CIP Go gauge.  I rechecked several times to make sure things were consistent.  I also checked the difference between having the bolt stripped or fully assembled, and as long as the gauge was carefully guided into the chamber, the results were the same.

I don't know exactly how forgiving these rifles are.  I did unwittingly fire one for 1200 rounds with no problems even though it didn't close on a SAAMI Go gauge.  Regardless, I didn't feel good about that and spent some time switching things around until I got all three rifles to close on the SAAMI Go gauge (easily on the CIP), while not closing on the SAAMI No-Go (and neither on the CIP No-Go).  Clearly, it's important to be careful when exchanging parts other than just the bolt. 

[Centrone22]

TjNewton your lug that broke off  is the same one that broke off of mine. I scared to think it may be a reoccuring problem

[TJNewton]

TjNewton your lug that broke off  is the same one that broke off of mine. I scared to think it may be a reoccuring problem

Centrone22, I did an extensive search and found only one occurrence other than yours and mine.  Considering that there are only three reports among thousands of posts online regarding the VZ58, and considering that the VZ58 has been in service for sixty years while retaining its reputation for reliability, I don't think it's a big problem and probably isolated.  Everything eventually fails and it's possible that either these three failures came from the same subpar batch of bolts, or just had several thousands of rounds of punishment, most probably in full-automatic fire.

I re-headspaced my three rifles and have tested fired two of them, including the one with the replacement bolt.  So far, so good.  The spent cases and primers have no abnormal wear and accuracy is where it should be.

[MeatAxe]

TjNewton your lug that broke off  is the same one that broke off of mine. I scared to think it may be a reoccuring problem

As I posted in your thread, if you could post the first 4 or 5 digits of your gun's serial number, somebody here might have a CSA rifle in your range that might have some additional info.

[Centrone22]

Update: i picked up my rifle today as it came back from warrenty and they replaced the bolt and piston. The reasoning for replacing the piston according to the factory was that the rifle was being overgassed and it put extra pressure on my bolt leading to the lug shearing off. The new piston they gave me has a concave piston head where i had a flat piston head before.

[TJNewton]

Update: i picked up my rifle today as it came back from warrenty and they replaced the bolt and piston. The reasoning for replacing the piston according to the factory was that the rifle was being overgassed and it put extra pressure on my bolt leading to the lug shearing off. The new piston they gave me has a concave piston head where i had a flat piston head before.

Thanks for the update.  Good information.

Approximately how far did your VZ58 throw casings before the bolt broke?  Mine throws them about 4-6 feet, pretty much straight up or slightly to the right.  It would be interesting to see if the new set-up throws them differently.

[TJNewton]

Checked my gas pistons.  I have four Century US-made, and four Czechoslovakian surplus.  The Century pistons are all concave, and three of the surplus are flat, with one being concave.

Were the concave pistons regularly used by the Czechoslovakians to tune individual rifles?  Also, how to determine if a VZ58 is over-gassed?  All of mine throw spent shells as though they were secondary projectiles of attack.  My SKS's throw them just as violently, but I noticed that their gas pistons are also concave.

[Centrone22]

My shells were also ejecting about 4-6 feet but i have fired my rifle with the new piston yet so ill have to let you know on that one

[TJNewton]

From what I've experienced and seen online, every V58 variant ejects cases violently.  I'm not sure what the measurement or threshold for "overgassed" may be.  The new concave piston may be a safeguard, just in case. 

I may consider switching back to the concave Century pistons; they worked without problems and I switched to surplus mostly for the chrome benefit when cleaning.  I believe the problems with Century pistons were with an earlier generation.

[Centrone22]

Went to the gunrange last weekend spent five hours shooting my vz58 sent hundreds of rounds down range with the concave piston and it performed flawlessly same 4-6 foot shell ejection as my friends surplus cz58 with the flat piston.

[TJNewton]

Thanks for the report.  I also went to the range and tested different pistons:  Concave Century and both flat and concave surplus.  It wasn't a completely scientific comparison, but I didn't notice any difference in the ejection distance or force either.