Checking Headspace on a VZ.58 - Procedure / Variations?

[CitizenPete]

Recently a user posted that they returned their VZ2008 to Century because of improper head space. So, this got me thinking that I have never checked head space on ANY of the VZ.58s in my collection, or any that I have sold in the past.  Therefore, I ordered a set of CLYMER - GO/NO-GO GAUGE SETS from Brownells:

184-000-039WB
7.62x39 Headspace Gauge Kit
Mfr Part: GONG762X39
http://www.brownells.com/gunsmith-tools-supplies/measuring-tools/headspace-gauges/go-no-go-gauge-sets-prod26876.aspx

I have 7 VZ2008 carriers at a shop to be tabbed, so I couldn't check them yet, so I tried a CSA (Czechpoint) and an OOW VZ2000.

I checked head space the same way on both
The chamber and carrier/bolt face were wiped cleaned and the striker was left out. It did NOT remove the firing pin or the extractor from the bolt.  No magazine was on the bench or involved in any manner.

The carrier, bolt with locking lug were put into the receiver and moved forward just past the ejector.

Then I carefully inserted the GO gauge rim under the extractor on the bolt face and slowly guided the gauge into the chamber and closed the carrier/bolt on the barrel.  The locking lug tabs were in place in the rail slots and the carrier went all the way forward.

Then I did the same with the NO GO gauge and the locking lug tabs were in place in the rail slots.  Why? I would think the locking lug would NOT drop into the slot in the rails with the NO GO gauge.  ALSO, the carriers would not close all the way forward in the receiver with the NO GO. The front of both of the carriers had an open gap of approximately 5/16" between the front of the carrier and the block on the receiver where the gas piston hits the carrier face.  I did NOT try to force it forward but applied enough forward pressure that it should have closed if it could.

What is the proper method for checking the head space on a VZ.58? Why does the locking lug go into the slots with the NO GO gauge?


 

[Enthusiasm]

Tag.  This is one area were I am lacking in knowledge. I just fire three rounds and then look at the caseings, if they look normal I assume this rifle is working.

[muggia59]

That site had me wondering the same. Last time I used a go/no go gauge was on the 50 cal in the late 80s, early 90s.

[RSR]

The bolt locks tighter as the locking piece falls down.  So it's possible it didn't drop all the way down but caught enough to catch...

These two posts are pretty good:

http://www.projectguns.com/vz586.html

http://www.czfirearms.us/index.php?topic=49281.0

And there is a lot of other info on checking headspace on the ORF self-builds as well.  Looks like you use the bolt and locking piece by itself...

[CitizenPete]

The bolt locks tighter as the locking piece falls down.  So it's possible it didn't drop all the way down but caught enough to catch...

These two posts are pretty good:

http://www.projectguns.com/vz586.html

http://www.czfirearms.us/index.php?topic=49281.0

And there is a lot of other info on checking headspace on the ORF self-builds as well.  Looks like you use the bolt and locking piece by itself...

Thanks for the reply.

I had already reviewed the (ibid) post in your second link earlier today, but it offered no answers to my questions.

As for the Project Guns link, it does not answer the question as to why the locking lug still goes into the slot when the NO GO gauge is used.  They are setting the barrel position with a GO gauge or round with some tolerance (.004) left intact for settling back after operation. Not certain if this pertains specifically to a GO/NO-GO gauge check of a completed rifle. Certainly the GO gauge works.

The best I can tell the lug is as low into the rail slots with the NO GO as it is with the GO gauge.  I flipped the gun upside down visually examined that carefully, however it could be off a small amount since I did not measure it in any way.

In any event, lets just say for a moment that the locking is not going (dropping down) into the receiver the full depth as with the GO gauge, and because it is curved and not straight that it is holding the bolt back slightly. Certainly that does not explain why the carrier is held back from closing against the front receiver block (and end of gas piston) by a full 5/16".

Perhaps you can not use the NO GO gauge on a VZ.58 in this manner?

I have read several references within this forum and other sources regarding locking lugs. Evidently they are marked with different "code" numbers and others have surmised that they are different dimensions allowing them to me installed to adjust the bolt position or match the rail slots after the barrel has been installed and head spaced to the bolt,  however how does that make sense since the barrel position is set, pressed in place, drilled and pinned -- not based on the bolt by itself, but with the bolt and locking lugs setting the bolt face position.

Tomorrow I will reach out to OOW to see if they will donate the time on the phone to give me an explanation (that I can hopefully understand). 
I will also send an email to Czechpoint, however Dan is at HQ in the Czech Republic this week for meetings, and will have limited email access or time.
One other possible source of info on this topic might be my contacts at MARCOLMAR Firearms, who built my UK VZ-59.  They recently adjusted the head space on that gun for me because I found a NOS bolt assembly and NOS heavy barrel.  The UK59 carrier and bolt have a similar design to the VZ-59 only much larger and inverted.  (On a side note: the originally open bolt UK59 has removable barrels locked in by a top cover cam, and a carrier which includes a short piston pinned to the front of the carrier, similar to the AK carrier.) However, the locking lug piece looks almost exactly the same as the VZ.58, just bigger and there are also similar slots in the receiver rails.  So, I wonder if a 7.62x54R NO-GO gauge would show the same thing in the UK VZ.59?  Also, there are codes on the UK59 locking lugs as well.

Anyone have an inside source number at Century they could call?

If anyone has any additional insights on the NO-GO gauge test with the VZ.58 please post.

[r2d2]

Gonna go out on a limb here...

Just because the locking lugs lock with the NO GO doesn't necessarily mean the round will fire. What position was the striker in during these tests?

[Varickm]

Recently a user posted that they returned their VZ2008 to Century because of improper head space. So, this got me thinking that I have never checked head space on ANY of the VZ.58s in my collection, or any that I have sold in the past.  Therefore, I ordered a set of CLYMER - GO/NO-GO GAUGE SETS from Brownells:

184-000-039WB
7.62x39 Headspace Gauge Kit
Mfr Part: GONG762X39
http://www.brownells.com/gunsmith-tools-supplies/measuring-tools/headspace-gauges/go-no-go-gauge-sets-prod26876.aspx

I have 7 VZ2008 carriers at a shop to be tabbed, so I couldn't check them yet, so I tried a CSA (Czechpoint) and an OOW VZ2000.

I checked head space the same way on both
The chamber and carrier/bolt face were wiped cleaned and the striker was left out. It did NOT remove the firing pin or the extractor from the bolt.  No magazine was on the bench or involved in any manner.

The carrier, bolt with locking lug were put into the receiver and moved forward just past the ejector.

Then I carefully inserted the GO gauge rim under the extractor on the bolt face and slowly guided the gauge into the chamber and closed the carrier/bolt on the barrel.  The locking lug tabs were in place in the rail slots and the carrier went all the way forward.

Then I did the same with the NO GO gauge and the locking lug tabs were in place in the rail slots.  Why? I would think the locking lug would NOT drop into the slot in the rails with the NO GO gauge.  ALSO, the carriers would not close all the way forward in the receiver with the NO GO. The front of both of the carriers had an open gap of approximately 5/16" between the front of the carrier and the block on the receiver where the gas piston hits the carrier face.  I did NOT try to force it forward but applied enough forward pressure that it should have closed if it could.

What is the proper method for checking the head space on a VZ.58? Why does the locking lug go into the slots with the NO GO gauge?

The locking piece can partially drop on a no-go. Even if it drops completely on a no-go, it might still be ok to shoot. A field gauge determines whether or not a rifle is safe to shoot. It's also important to note that metal expands when heated. Manufacturers might find it beneficial to set headspace a little loose in order to compensate for this.....

[CitizenPete]

What position was the striker in during these tests?

Already covered...

I checked head space the same way on both
The chamber and carrier/bolt face were wiped cleaned and the striker was left out.

[CitizenPete]

One reply so far: On the UK VZ.59 head space and locking lugs:

With the Go gauge in the chamber the bolt should close completely, locking lugs fully engaged and the bolt carrier should go all the way forward til its up against the back of the bolt.

With the No-Go gauge in the chamber the bolt may go almost all the way forward and the lugs appear to be fully engaged but the bolt carrier won't fit tight up against the back of the bolt. The difference between the gauges is .003" which is a very small amount. This is not enough to keep the locking lugs out of the slots in the receiver and you may not note any difference in their location visually.

Lastly, headspace is normally checked with the firing pin and extractor removed as they can interfere. You need to be careful about slamming the bolt and carrier forward as the gauges are hardened and brittle. The extractor can break the rim off the gauge quite easily. Broken parts of the gauge can damage the bolt face and chamber as well.

SO, guessing that the VZ.59 is similar, I'm wondering if you could somehow use a .004 feeler gauge at the front of the bolt? to measure the gap while the NO GO gauge is in place with just the bolt (carrier removed?). ...or between the bolt and carrier somewhere?  WTH? I'm guessing here???

[CitizenPete]

One more reply by phone:

Everything I outlined in my original procedure is correct ( * ) and the results I saw actually show proper head spacing.

So... From what I understand:

GO Gauge should allow bolt and gauge (round) to close fully on the barrel chamber, and the locking lug to fully engage into the receiver slots. The locking lug being fully engaged and thus not obstructing the carrier in any way, the carrier face (where the stripper guide is located) can fully close on the receiver block to meet the gas piston.

NO-GO gauge will allow locking lugs to engage (but not fully), but the bolt will have a .004 gap on the chamber and the carrier will not go forward fully.  The locking lug not being fully engaged into the receiver prevents the carriers forward motion, resulting in that 5/16" gap between the bolt carrier face the receiver block where the gas piston hits the carrier.

( * ) Noted that extractor and firing pin should be removed, as the hardened steel gauge can easily be damaged and they can interfere.

I guess when head space is OFF, you would see the locking lugs close fully and the carrier all the way forward with the NO GO gauge (ex. barrel not in receiver far enough), and possibly with the GO gauge you would see that the carrier does not close fully (ex. barrel too far into the receiver).

A while back Dan at Czechpoint mentioned that on rare occasions swapping carriers might affect head space.  Now that makes more sense to me.

[JohnEd]

 The difference between the gauges is .003" which is a very small amount. This is not enough to keep the locking lugs out of the slots in the receiver and you may not note any difference in their location visually.

I remember this from my distant past.....the difference between a go and a n o-go was supposed to be .003.  We made a "No-Go gauge" by adding a couple thicknesses of Scotch Tape to the bottom of the Go gauge.  That is adding .004 to the Go and that worked in bolt guns.

I just tried a Go in my 58 and it closed and the trigger fired.  I added the tape to the gauge and it still fired even though I had added, supposedly, .001 MORE than the required amt to make a No-Go gauge.  I chambered a NO-Go gauge and the gun still fires.  By fires I mean that the striker drops.  The locking lugs appear to be fully engaging in all cases.  There is a story out there that the Go Gauge needs a .004 shim installed during the barrel pressing operation to ADD SPACE to allow for somthing to settle in and this seems to cancel proper head space....sorta.

Would it be useful to keep adding tape layers to the Go gauge to determine when you get a No-Go condition?

My brass and primers look good and the gun runs fine.

The no-go is marked "CIP 12/14 MANSON" but the Go isn't and has "PTG 3/12" on it.

I am building two new guns and i need this information to do it safely.

Thanks,

John

Pete....many thanks for all the info and spending time with me.

[RSR]

ORF might still have some tools/directions to assist in this seeing as how they're still selling the receivers.  They did offer and probably still do, some jig that helps when pressing in the barrel.  Imagine it has a headspace component to it as well...

[CitizenPete]

ORF might still have some tools/directions to assist in this seeing as how they're still selling the receivers.  They did offer and probably still do, some jig that helps when pressing in the barrel.  Imagine it has a headspace component to it as well...

ORF is long out of business, no?  Assault Weapons of Ohio took their inventory I believe, but are mostly sold out of everything - at least thats what they told me a few weeks ago.  But I could be wrong.

[tubee1]

Try checking the headspace with the carrier and striker installed. When the headspace is correct the striker will travel all the way forward with the go gauge installed but not with the no go gauge. It is a little tricky to get just right as very little barrel movement changes how far the locking lugs drop down into the receiver. Also it is easier to feel when it is correct with the extractor removed. If the headspace is slightly tight I find it easier to use marking compound and file the receiver rails to obtain the proper headspace as opposed to pressing the barrel out. If the headspace is excessive the only remedy is to press the barrel in further or try swapping bolt and locking pieces around.

[CitizenPete]

Try checking the headspace with the carrier and striker installed. When the headspace is correct the striker will travel all the way forward with the go gauge installed but not with the no go gauge. It is a little tricky to get just right as very little barrel movement changes how far the locking lugs drop down into the receiver. Also it is easier to feel when it is correct with the extractor removed. If the headspace is slightly tight I find it easier to use marking compound and file the receiver rails to obtain the proper headspace as opposed to pressing the barrel out. If the headspace is excessive the only remedy is to press the barrel in further or try swapping bolt and locking pieces around.

Just to confirm:

"Filing the rails" refers to the "opening" the two slots larger by filing in the rear of the openings for the the locking lug.