VZ 58 Gas Piston Diameter

Steve07

Steve07

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Has anyone put a caliper on the head of a replacement piston in a VZ 58 223 Rem that has had the piston replaced for the excessive ejection pressure issue?

Piston diameter on both of mine is 0.473". Need a rough idea what these are being replaced with beyond "a slightly smaller" piston as in the note from CSA. How much is slightly?
 
Just measured mine came in at 0.466. Mine was replaced although I believe they may of just took it to a lathe and shaved it down. Could be wrong but the head of the piston was way to dirty and caked on for only 20 test shots.
 
Hmm, interesting. Wouldn't surprise me you are bang on with your suspicion.

In the category of good guesses, I turned mine down to 0.465" and am going to go see what happens. Just haven't had a chance to try it yet.
 
Just to add, cz858 7.62x39 is same as op 0.473" unaltered. It appears that is the stock diameter in both the 7.62 and .223 models.

Edit- I see you guys already knew that haha so my post is pointless! Too many beers last night I guess
 
I would guess that the piston is pretty standard, as by my fuzzy logic, the issue comes from incorrect gas port size on some barrels. So hopefully, the piston-swap fix is easy and reliable.

But again, it's my guess...
 
MY VZ chucks brass over 5 meters away I have been considering doing something to the gas piston myself. I have a mini lathe and decent machining skills but I had been thinking of boring a small recess into the face of the piston. How well is the under sized piston working?
 
Well I gave it a go this morning at reducing the diameter of the piston slightly. Worked really well. I went to the range with my calipers and cordless drill and a oil stone. I'd take a couple thou off and then fire a few rounds. Started off at .472" and ended up at .466". Now it chucks the brass nicely 3-6 feet away and they aren't dented to uselessness. I can easily reload this brass, and FIND it.
 
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