this is pretty unsettling. those lugs impact on the barrel below the chamber.
I see three possibilities -
1. the bolts are old, worn parts
2. the design of the bolt is inadequate - more reinforcement is needed for those lugs. the cause of the failure could be repeated pressure from expanding cartridge cases
3. headspace is too tight, putting extra stress on the bolt
one thing is for sure - the CSA .223 version of the rifle has new manufacture bolts
I did an extensive web search and could find only one other account of this breakage beside Centrone22's and mine. That seems to make three total. I suspect that it's excessive wear-and-tear. If it were a design flaw, I think the problem would be more widely reported, perhaps on the level of broken SKS firing pins or Beretta 92 locking blocks. I've read more accounts of VZ58 strikers or firing pins breaking, but those are also rare, fewer than a half dozen. I've seen just one account of a VZ58 locking piece breaking from being dropped onto the floor.
It could be that these three broken bolts were all subjected to tens-of-thousands of rounds of automatic fire in their previous rifles. It could also be that there was a bad shift at the foundry one Monday, Wednesday, or Friday anytime from 1958 to 1984, producing the faulty bolts from these three accounts. It could also be the few hundredths or thousands of an inch of variances between the several surplus moving parts and the American-made receiver that created cumulative stresses on that one lug. Impossible to tell, of course.
It seems that despite the generous tolerances of the VZ58 design, there are some incompatibilities between parts made at different times from different factories. In swapping parts between my VZ2008's and surplus kit, I've found that most interchange, but some have or would need fitting to be transferred. One of my dust covers won't snap down tightly on one of the other rifles; it would fit with some minor filing. I've experienced that with hand guards as well. Some front sights are loose in some block sights and require Loctite. Some strikers drag very slightly in some receivers, etching a pair of shiny strips in the receiver, while in others the more forward completely freely. Forced March put up a video a while back going into detail on some differences between the moving parts.
I know it's been brought up before, but I'd like to know the significance of the stamped numbers on the locking pieces. Mine have a sideways "3", and vertical "06", "07", and "11". Do they account for correcting worn head space? If so, that would be ingenious. Are they irrelevant if the head space is good? The bolts have different numbers etched into the sides, some with a with a circled "T". Considering the difficulty of research due to the time and language barriers, theses questions will probably remain rhetorical.
