Is the tab needed because the gun is changed to a semi auto only mode with a different trigger group part or two?
No, it has more to do with a slight shift in trigger components, slight variances in them due to fit or wear, and to flexing of the trigger mechanism feather. Basically, the fire control group fails to reset correctly when the bolt carrier slides to the rear of the receiver, resulting in a misfire and /or jam. It may be remedied by flexing or shimming the trigger mechanism feather upwards or figuring out how to fix the amount of shift or wear in the fire control group. The tab seems like a more solid and sure method of avoiding the situation, whereas the shimming of the trigger mechanism feather with a small spring underneath it could be less permanent. Various other fixes have also been used, but involve filing the striker or trigger components, which I would not consider doing myself because they could be unsafe.
The tab is a piece of metal that is mig welded onto the bottom of the bolt carrier, which ensures that the disconnector resets, because it hits it when it slides backwards. You can see the tab on this bolt carrier CzechPoint sells. It is the rectangular metal piece on the right hand side of the photo. You may have to compare the photo to your own bolt carrier to see the tab welds.
http://www.czechpoint-usa.com/products/spare-parts-and-accessories/vz-58-parts-and-accessories/bolt-carrier/I had followed the gremlin subject with interest for about a year on the canadiangunnutz forum, just in case I ever had to deal with it personally. It seemed there was a higher incidence of gremlins on the Canadian VZ58?s than those in the US and they were working on ways to address it. It wasn?t until I purchased an aftermarket bolt carrier from Neit Arms that I noticed how it differed slightly from the CzechPoint carrier. In other words, I had not noticed that CzechPoint had permanently attached a tab to their carrier before assembling my rifle and had always assumed the rifle was constructed of stock components entirely. I had been waiting to see if the gremlin would somehow appear, but it was always highly unlikely due to the tab.
The Canadians cannot import the CzechPoint pre-tabbed bolt carriers from the US by mail, but can add tabs to their own carriers or find other ways to fix the problem. Some people have offered the tabbing service in Canada, but not in the US that I know of. I don?t know if Century or Ohio Ordnance uses tabbed carriers, but regular kit builds would not, because the bolt carrier is in a stock configuration.
I don?t have a clue how the military units have dealt with this problem before. Maybe the armorers and soldiers make a practice of pre-bending the trigger mechanism feather as part of regular maintenance. I do not know who first invented the tabbing fix or when either, but it seems to work. While I do feel that I am being somewhat paranoid about this, but would never want my weapon to misfire when I needed it to fire, and the means to avoid it are available.
