piston blowback issue using different ammo cz858

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dsmart

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Ive shot around 600 rounds of the standard corrosive surplus without a single issue. I tried using some sellier and bellot lead core hunting rounds the other day and the gun doesnt seem to like them. It would fire but the piston would come farther back then normal to the point where every shot would result in the piston popping out of the front gas chamber and jamming itself....resulting in a failure to reload. I should have taken a picture but I hope my explanation makes sense. The bullets are 123 grain which is the same as the corrosive ones but the powder load is not listed. Wondering if anyone else had had a similar experience? Cheers
 
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Sounds like more of an issue with the top cover? I think the top cover has an area machined out to allow the piston to only come back so far and not all the way out.

Did the ammo seem more high pressure? Brass damaged?
 
The ammo did seem to have more power than I remember but its hard to say as I haven't shot the gun in awhile. I haven't had a chance to see if its still mis-firing with the surplus stuff but when I do ill report back.
 
Update today. Had the rifle out and shot the usual surplus stuff. The gun did the same thing which rules out the ammo being the issue. I recently put a aluminum quad rail on which is the only other change. Could it be a worn out spring or bent piston? Everything else about the gun is the same. Ive put 600 plus round through it since new with not a single issue....now it wont cycle without this issue. Have pictures but cant post them basically imagine the piston hung up on the lip of the gas block
 
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Wilks said:
I had this issue, turns out an aftermarket quad rail had slightly deformed the gas block, had to take a file and clean the edges of the gas block then it worked fine.
Click to expand...

Ill have to check out the gas block more carefully. The quad rail I have doesnt attach anywhere to the gas block but maybe there is something going on in there. Here are some pictures of what it looks like when it happens.


 
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To me that looks like the rail that hit the market a year or so back that was sold for the CZ 858 and VZ 58 family but there were issues with the rail not being properly made for this rifles.

Here is what the inside of my NEA upper looks like, that channel allows the piston to move back and forth and I believe it also prevents the piston from doing what yours is doing...

photo%2B%282%29.JPG
 
I'm still fairly new to this weapon system but my money is on the upper being the issue.

Do you still have the stock upper? If so test fire with the factory original upper installed...

If the problems go away you could possibly cut and fit the original upper inner assembly to fit the railed upper.
 
G.Mitchell said:
I'm still fairly new to this weapon system but my money is on the upper being the issue.

Do you still have the stock upper? If so test fire with the factory original upper installed...

If the problems go away you could possibly cut and fit the original upper inner assembly to fit the railed upper.
Click to expand...

Those exact idea's were just being pondered. Thanks for the heads up about the upper being a "piston guide" of sorts....I never would have thought that. Ill report back when I get a chance to go shooting again
 
dsmart said:
Those exact idea's were just being pondered. Thanks for the heads up about the upper being a "piston guide" of sorts....I never would have thought that. Ill report back when I get a chance to go shooting again
Click to expand...

My pleasure.

This is a great place to learn, I'm happy I could help. Hopefully you'll have better luck with the stock upper cover. I'm sure it could be modified somehow to work under that upper rail.

Good luck.

Keep us posted.
 
That upper handguard just looks wrong. I have the BC tactical and it has the 2 prongs that fit snugly under the 2 tabs on the gas block just like the stock one does. It also forms a full cover over the piston at the gas block end. Based on the first picture, does it expose the piston when you have it installed - sure looks like it??

Can you post a pic of the whole upper rail - it almost looks like an AR rail mounted backwards....
 
There is a link on page one to the ebay page that has some pictures of it installed. The rail system clamps to the barrel on the inside. It does expose the piston more than other rail systems ive seen. I never considered that to be much of an issue as I thought the upper hand guard wasn't even needed for proper operation. At the end of the day the price was why I bought it, the plastic fab fore ends are a joke (no offence to anyone who uses them intended) and the other aluminum rail systems aren't worth the $300-400 for me. I wanted the bonesteel set but he couldn't me an idea as to when he would have them back in stock. If I cant get this rail to work then ill go back to stock and wait for bonesteel to ship me theirs.
 
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Im in Canada. At the time I contacted them they had none in stock and didnt know when they were getting more. Im not yet ready to give up on the one I have now...although the bonesteel one would likely allow co-witness which would be a bonus. The one that I have now does allow the use of the irons with the optic removed though
 
Managed to modify and use the original upper (without barf) under the quad rail. There is a small hump under the factory upper that sits right where the piston would slide back into the gas block. Im guessing that's what guides the piston back into the block. Ill update after shooting if all is well. Thanks for all the help on this
 
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