Bolt carrier diet and an adjustable gas system

[Samikoo]

As I use my VZ-58 in competition, I started wondering if I could lighten the bolt carrier a bit. The results from a diet on AR and AK bolt carriers are great, so why not do the same with the VZ?

So, has this been tried before? If so, what were the results?

I know I will need to adjust the gas system and use lighter recoil springs if I intend to take full advantage of the lighter carrier.

[ReverendOlaf]

Never heard of anyone doing that.  What's the benefit?

I did polish my bolt carrier to help it work better with my railed slide cover. 

Good luck!

[Samikoo]

Never heard of anyone doing that.  What's the benefit?

I did polish my bolt carrier to help it work better with my railed slide cover. 

Good luck!

Lighter reciprocating mass means quicker follow-up shots. And the felt recoil turns from a long push into a short snap, allowing the sight(s) to return to target faster.

If the bolt carrier is lighter and the gas system is left alone, the lighter carrier will be moving a lot faster than it did before. Therefore it is necessary to restrict to amount of gas getting to the piston.

If the carrier has had a succesful diet and the gas system is tuned properly, the stock recoil spring will send the carrier back to battery with too much force, making the rifle "nod".

From the three modifications listed above, making an adjustable gas system would give some benefit if done alone, especially if a suppressor is used. These battle rifles are usually over-gased, in order to work properly when really dirty and so on.

So, there seems to be a lot of "excess" material on the bolt carrier, I'll just have to see where it can be removed safely. Can anyone confirm if 7.62x39 and .223 recoil springs are different? Or if the bolt carriers have some major differences?

And you can always try to make a new gas piston, or mess with the old one, to save some weight.

[RSR]

In addition to the recoil spring hole, striker hole, the bolt carrier already has two parallel lightening holes between those two...

Not sure what else you can do there?  There are some different generations of bolts and strikers that might save you a little weight in their construction, but as far as the bolt carrier itself, I'd be hesitant to do much tinkering...

Maybe widening slightly the existing lightening holes?  But this rifle is a very well engineered weapon, and seemed to have placed a premium on as light as weight as possible throughout its construction...

[Samikoo]

I'll see if I can find pictures of a modified ak bolt carrier just for reference of what can be done...

E:


Picture stolen from the internet.

An AK bolt carrier, bolt and gas piston weighs a massive 503g. VZ-58 bolt carrier, bolt and gas piston combined, 548g. The gunsmith who performed the diet on the AK parts removed 229g, so the parts ended up at the weight of 274g. So I think there is material to be removed, safely. If not more than a hundred grams.

I did notice the new style bolt would be lighter than the one I'm using, but not by much. Since gas pistons can be had from the Czech Republic for a couple of bucks, I think I'll experiment with those too. I would also need a new bolt carrier since I'm hesitant to sabotage the one I have now.

[zukiii]

I believe CAI also did this with there Centurion C39 rifles.

[CitizenPete]

Darn it! ... And here I am adding weight to my carriers by getting them "tabbed".   

[Samikoo]

Here are some photos of the AK carrier, just to show much thinking outside the box it may take to actually achieve something. If you click the pictures, they may suddenly appear larger.









Those pictures show the unfinished product, with some deburring and polishing to be done.

The upper gas tube was made of aluminum tube with a wall diameter of 1mm, just to see what it could take, but it bent after about 1000 rounds. It was replaced with a stainless steel tube.

So, I think our VZ carriers have some excess material, too.

[Samikoo]

I decided to try if I could take a little weight off the carrier. Who uses stripper clips anyway?



This modification netted only 13 grams of weight loss, so I doubt if 100 grams is a reasonable goal. Maybe if all the weight (to be) taken from the locking piece, gas piston and bolt carrier combined would add up to that it might be done. We'll see.

[RSR]

Another option: http://canadatargets.com/products/vz/vzbuff.html

Vz58/Cz858 Buffer

Like many of you we are big fans of the cz/vz58 platform. The ammo is cheap, readily available in bulk, and the rifle is robust (no finicky little springs to deal with).

We had a chance to play with a buffer add-on for the cz/vz platform.

The buffer can be installed in less than 5min with no tools. Based on our tests with a shot timer the rate of fire increased by 40-50%.

The gentleman that presented these to us also says that it reduces felt recoil; but we don't find much recoil with the 7.62x39 to begin with and had no objective way to measure it.

[Samikoo]

I've never seen one of those. I wonder if it increases malfunctions? The buffer seems really thick, and I know my bolt carrier slams against the receiver covers rear face. The buffer I had in mind was like one third of that. That buffer should be sending the carrier forward quite fast...

Since I can't adjust the gas system yet, I won't be taking any more material of the bolt carrier. Based on comments from AR and AK-guys the biggest single modification is to cut the amount of gas. And if I have a lightweight bolt carrier and standard amount of gas, things will be moving along a lot quicker... That's why I wan't to be able to start from barely being able to cycle the action, and then giving it more gas to find the sweet spot.

I know my bolt carrier isn't light enough to cause problems (yet), but I like to stay on the safe side. Then, as I remove more material, I can just shut the gas and start adjusting from scratch.

[Samikoo]

Since there is a short break from competitions I decided to get the adjustable gas system done.



Tools I used were a cordless drill, a 4.2mm drill bit, an M5 tap and a small adjustable wrench. And some cutting oil. Did the work in my bathroom, to maximise the possibility of a screw-up.

Next I need to modify the M5 hex bolt since with the tap I had I was unable to thread the hole until the very bottom. I should be able to shoot the rifle on Tuesday to see how it works.

[armoredman]

That's interesting. Looking forward to seeing how this works.

[Samikoo]

This is what the bolt looks like. Now I can shut the hole for good, so shooting subsonics will be quiet since there will be no movement of the bolt etc.



And finally I got it all done. I won't paint it untill I have testfired the bleep thing tomorrow.

[Samikoo]

So I got to the range today, and shot 90 rounds. At first I tried if I could keep the action from cycling, and I did. The bolt carrier did move a bit, but not enough to eject the spent case. So further modification of the screw would be in order.

Next I opened the screw a bit, and shot a short drill. The spent cases flew a foot high, and I encountered one stovepipe. So I opened up the screw a little more, and had zero malfunctions.

Then I tried the rifle with gas port fully open. The difference was quite big, as I was able to get back on target faster with the gas restricted.

Now I can continue to remove material from the bolt carrier to see if there is anything to be achieved.