Cetme Bolt Gap and Headspace


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Drakejake
October 10, 2006, 02:39 AM
I am familiar with two of the Cetme discussion groups, but I know this topic has been discussed here as well. I am new to rifles and new to Cetmes. I know that you check headspace on the Cetme by checking the bolt gap with feeler gauges. I know the proper range of this gap and my rifle falls within that range, but it has a ground bolt head. And yet I am unsure of the relationship between bolt gap and head space. Does larger bolt gap mean less headspace or more headspace? I take it that the danger is that there is too much headspace and so the case is unsupported and could burst. Right or wrong? Grinding the bolt head is supposed to give a false reading of larger bolt gap, but does this mean that headspace might be unsafe?

Thanks,

Drakejake

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ceetee
October 10, 2006, 09:41 AM
As the gun is worked, the parts will wear. As the parts wear, that gap gets smaller. When the gap runs below proper specs, the gun's not safe to fire. As I understand it, "headspace" is not exactly the proper word for it. It also has to do with the timing of the bolt head unlocking and the bolt coming out of battery too fast.

jklinstein
October 10, 2006, 10:14 AM
Drakejake,

Ceetee has it right. This isn't "technically" a headspace issue. It has to do with the ability of the rifle to "lock up" and the timing of the unlocking. In essence the ground bolt can lead to the locking piece coming to rest on the bolt head instead of being fully supported by the rollers. When this happens it's become an unsafe rifle. The worst case scenario is that it will begin ejecting too soon, allowing the unsupported (soft) brass case to explode, tearing up your rifle and maybe some parts of your body.

My CETME is at Century, waiting to be looked over. I bought it in '02, but have been hesitant to shoot it for the last 3 years, ever since I found out that I had a ground bolt head. I purchased an unissued bolt & carrier assembly (new from an armorer's kit), put in the largest rollers available (+4's), and still had less than .003" bolt gap. If you send me an email I'll let you know how Century responds to my out of spec rifle.

If Century offers less than $300 I'll ask for the rifle to be returned, or for a substitute that is at least as valuable as a working CETME.

Thin Black Line
October 10, 2006, 10:22 AM
I have seen some very scary looking CETME and G3 copies recently. One
actually had a "break" through the left side of the receiver where it looked
like the stamped bolt guide had been taken in too far and split. It was not
far behind the trunion area. I told the salesman at (big box spotrting goods)
"this is a major problem and should be sent back." They sold it the next
week anyway.

If you really want a semi 308 and must have a G3 copy, there are still
HKs out there, but also used Springfields and new PTRs. Likewise, there
are a lot of good FALs --DSAs and decent builds using Imbel receivers.

Drakejake
October 10, 2006, 05:35 PM
WHAT CENTURY JUST TOLD ME AND FURTHER COMMENTS

A new bolt head is about 1.835. Century's minimum spec is 1.825. My bolt head measures 1.816, using digital calipers from an auto parts store. I talked to the Century gunsmith Keith. He said there was a safety issue and the bolt head needed to be replaced. Otherwise there could be case separation, although this would not be an explosion. They have new bolt heads but will not send one to me. I must return the rifle and pay for shipping to them. I think I will buy a new bolt head and try to solve the problem myself. I am told that the bolt head comes with the rollers installed. I believe these can be replaced to get the correct bolt gap. I have just ordered a complete new bolt assembly from Makarov.com, about $81 including shipping.

I think I understand the headspace issue now. With an unground bolt head, and following the procedures for checking bolt gap described elsewhere, a gap of .005 to .019 gives safe headspace at the other end of the bolt. If you grind the bolt head to get a decent bolt gap, you have a false reading because the front of the bolt head does not extend as far towards the chamber. The proper gap reading indicates head space only if the bolt is normal length, about 1.835. Grinding the bolt increases headspace with the Cetme operating system. So I suppose there are operating issues that could lead to case separation, but my main concern is excessive head space. I examined a number of fired cases and did not see anything out of the ordinary. If I had been shooting .308 instead of surplus 7.62 by 51, I might not have been so lucky with my out of spec rifle. My intention is to try the replacement bolt head and see if that solves the problem.

Those who know more about this than I, please correct me.

How Century could have sold a rifle that is not even up to their minimal standards puzzles me, given the liability issues involved. My rifle is only a little over two years old.

Drakejake

Thin Black Line
October 10, 2006, 05:43 PM
How Century could have sold a rifle that is not even up to their minimal standards puzzles me, given the liability issues involved.

And the last one I saw with light shining from the ejection port through the
other side of the receiver should not have left the factory. IMHO, somone
there was asleep when it has come to the QC for the CETMEs.

On the flip side, the Yugos and FALs they're sent out have been nicely
put together......different subcontractors???

Ian Sean
October 10, 2006, 07:54 PM
and FALs they're sent out have been nicely
put together

Ummmm, in short...no.

An FAL assemled by Century is and has been a 50/50 crap shoot. The recievers (poor quality or out of spec), the builds themselves (headspace, barrel timing etc...)had have many documented errors and bad builds. I wish they would get out of the business, for OUR sake.

If there is ever a successful lawsuit against a manufacturer for hurting or killing THE GUNS OWNER SHOOTING IT it will be against them in my opinion.

Century got the nickname "angry beavers" for a reason. Please check the FalFiles for full info on Century products over the years.

Drakejake
October 11, 2006, 03:30 PM
The idea that a ground bolt indicates excessive headspace and an unsafe condition really assumes that the barrel was accurately pressed into the receiver. One might assume this if the Cetme were in its original condition and had not been reassembled to a new receiver. My concern is the possibility that Century ground the bolt head, not to cover up worn parts/excessive head space, but to compensate for inaccurate pressing of the barrel into their new receiver. If the barrel was pressed slightly too far into the receiver, this could cause inadequate headspace so that rounds could not be chambered and fired. To compensate for this problem, and to make the rifle functional, Century may have increased headspace by grinding the bolt head. So my rifle could be safe despite the ground bolt head. I suspect that replacing the ground bolt head with a new one may prevent the rifle from firing and may cause other problems. Am I totally off-track or do I make a valid point? Comments?

Drakejake

Thin Black Line
October 12, 2006, 12:48 AM
An FAL assemled by Century is and has been a 50/50 crap shoot. The recievers (poor quality or out of spec), the builds themselves (headspace, barrel timing etc...)had have many documented errors and bad builds. I wish they would get out of the business, for OUR sake.

Guess I'm just lucky with my Century Israeli HB on an Imbel lower that
shoots 1" groups. Then again, I've read a lot of complaints about FALs
UNTIL the new owner learns how to adjust the gas tap and uses
some good mags......but, sure it's a "bad build" until then.

MD_Willington
October 12, 2006, 01:53 AM
A friend has a century cetme, rips cases apart all the time... I've seen the century cetme, maybe not all, accept the TSR trigger groups that are available in some places... something I'd really stay away from.

Ian Sean
October 12, 2006, 02:25 AM
Guess I'm just lucky with my Century Israeli HB on an Imbel lower that shoots 1" groups. Then again, I've read a lot of complaints about FALs
UNTIL the new owner learns how to adjust the gas tap and uses
some good mags......but, sure it's a "bad build" until then.


I'm glad you have a good one, usually when Century builds them on Imbels they are known to be better.

I currently have 3 (2 G-1's on Imbels and 1 Argie on a Dan Coonan) all are home builds and I have built 7 total, and helped with many repairs. Over the years I have bought and returned 2 century recievers. One had the gas piston hole drilled off center about 1/8" the other had the ejector block installed and pinned too high to function.

I have helped several others fix under and over timed barrels and the worst was one that wasn't properly headspaced, seems someone at Century decided instead of replacing the locking shoulder they decided to grind away on the bolt.:uhoh:

The recent spate of poor Cetme builds is no suprise considering thier history with FAL builds.

Drakejake
October 12, 2006, 12:55 PM
MY PLAN:

When I get the new Cetme bolt assembly parts set, I will install the unground bolt and see if I can chamber a round (firing pin removed). With unground bolt, bolt gap should disappear completely, but I will install new locking piece to increase bolt gap. If with these changes rounds cannot be chambered/ rifle will not go into battery, I will probably assume that bolt was ground to INCREASE headspace to working spec rather than to give false reading of proper headspace. Does this make sense?

Drakejake

Thin Black Line
October 12, 2006, 02:32 PM
I'm glad you have a good one, usually when Century builds them on Imbels they are known to be better.


I've heard there are no more Imbels coming in....true?

ceetee
October 12, 2006, 03:15 PM
Drakejake:

As I understand it, t's not really a case of the bolt head moving rearward to increase the size of the chamber. If you think about the way it locks up, the locking piece presses the rollers outward with a good amount of force when in battery. If the parts are worn, the bolt gap diminishes. If the bolt gap is zero (or worse, less than zero) then the rollers won't have as much force behind them, pressing them into the trunnion recesses. Therefore, when you shoot, there won't be as much force delaying the bolt from moving. The bolt will move rearward earlier. If the bolt moves rearward earlier, the casing can (possibly) begin to be drawn out of the chamber before pressure has dropped enough.

The result is a blown case.

Along with a new bolt, and locking piece, you should get some +2 and +4 rolelrs to keep around, just in case. If the new locking piece alone doesn't give you a decent bolt gap, try the oversized rollers. They're very easy to replace.

Regarding the barrel being pressed back too far into the receiver... that is a real problem. I don't know how you could tell that, but I know there are HK-specific gunsmiths that can take it apart and repress it so that it's correct.

Maybe somebody else knows how to tell if our barrels were pressed properly...

Ian Sean
October 12, 2006, 07:01 PM
I've heard there are no more Imbels coming in....true?


That is correct :mad: , as with barrels the Imbels are banned also (reciever ban and barrel ban...non-sporting purposes :barf: ), a few are still out there, but you will pay a premium for them. Best alternative is the DSA or if DC Industries gets to making recievers again.

ceetee is right on describing the bolt gap issue and the locking roller operation and danger of no gap (blown case).

Drakejake
October 14, 2006, 06:47 PM
OK, today I got a complete unused bolt assembly from Makarov.com. As expected, with the full-size bolt head in the rifle, the bolt gap, which was .010, disappeared. Adding the new locking piece did not create a bolt gap. Adding the new bolt carrier made it very difficult to open the cocking piece handle and cock the rifle. Then I put the new bolt head and locking piece into the old carrier without the firing pin and loaded a live round into the chamber. The round seemed to chamber. My bet is that with plus four rollers, rounds would not chamber and the rifle will not fire.

So, with the ground bolt my rifle has a suitable bolt gap and works perfectly with no sign of case or primer bulging. With an unground bolt head and new locking piece, the bolt gap disappears. Now, as I understand it, adding plus four rollers will increase bolt gap only .004, not enough to meet standards. As I further understand it, my only recourse beyond replacing the rollers is to "repress" the barrel--basically reconstruct the rifle at a cost of several hundred dollars. My conclusion is that it is best to fire the rifle as it came to me and look from time to time for signs of excessive headspace. Or sell the rifle. I have another Cetme, with stainless receiver, on the way.

Drakejake

Drakejake
October 15, 2006, 03:16 PM
Using the new locking piece with the old, ground bolt head caused bolt gap to increase from .010 to .013. Is this good? Does this mean that headspace is smaller?

Drakejake

W.E.G.
February 21, 2008, 11:56 AM
Old thread revived...

Here is a bolt head I pulled out of a cosmoline enschlobulated kit from Centerfire Systems.

Notice the marks on the rear of the bolt head.

http://i227.photobucket.com/albums/dd7/rkba2da/rifle%20pics/CETME/boltheadfromkit.jpg

Here is how it measures.

http://i227.photobucket.com/albums/dd7/rkba2da/rifle%20pics/CETME/boltheadfromkitground.jpg

And here is a bolt head from a NIW bolt/carrier assembly

http://i227.photobucket.com/albums/dd7/rkba2da/rifle%20pics/CETME/boltheadNIW.jpg

W.E.G.
February 21, 2008, 11:58 AM
...and here is a pic "borrowed" from http://www.militaryfirearm.com/Forum/showpost.php?p=63326&postcount=5

http://i227.photobucket.com/albums/dd7/rkba2da/rifle%20pics/CETME/bolthead-groundbolt.jpg

Destructo6
February 21, 2008, 06:14 PM
There's a video on youtube that explains bolt gap very well.

http://www.youtube.com/watch?v=MFESb8TK7ZA&feature=user

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