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Dr Zero
Moderator



USA
2694 Posts
Posted - 02/08/2005 : 6:08:22 PM
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I have dug through the threads and this combo of info from Perro seems to put it out there simple enough.

What is the consensus?



What difference does a Ground Bolt make?

It mask the fact that the parts are worn out.
Its not the grinding of the bolt head thats important to all of this, its the fact that the parts are worn out and need replaced and when hacker arms grinds the bolt head, it takes away your ability to guage the wear of the other parts. THATS the dangerous part



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SIRUS
Gunboards Premium Member



USA
156 Posts
Posted - 02/08/2005 : 7:01:29 PM
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Its very nice to see photos of the crime that was done. After viewing the pictures many will pop out their bolts "just to make sure". I did and was found-unground. Thanks.


Jacobite
Moderator



USA
6102 Posts
Posted - 02/08/2005 : 7:03:20 PM
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Doc,
I have become board not being able to do any moderating so I made this a sticky as I feel it should.

We need to post what an unground bolt measures so those with ground bolts can compare. I know mine is ground but have mine in spec acounting for the amount removed.

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Don Nelson:

Git-R-Done!





Dr Zero
Moderator



USA
2694 Posts
Posted - 02/08/2005 : 7:59:21 PM
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Go for it Jacobite flex that mod power LOL

This is just the beginning of the ground bolt portion of the FAQ I have the other stuff to add.
I'm building it here so folks can have some input as it goes along.



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SIRUS
You are welcome! Kinda nasty when you look at it.

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www.drzero.org/coa
The Original CETME manual's Free for DL at www.drzero.org/cetme
Along with G3 manual's and now 21 AK and SKS manuals


Mecha
Moderator



USA
772 Posts
Posted - 02/09/2005 : 4:37:21 PM
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quote:
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Originally posted by Jacobite

Doc,
I have become board not being able to do any moderating so I made this a sticky as I feel it should.

We need to post what an unground bolt measures so those with ground bolts can compare. I know mine is ground but have mine in spec acounting for the amount removed.

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gave us these powers for good and evil and this board is so laid back and no in fighting of late no moderating to do is there? lol

Cake job

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FMP/HK 91
Beretta 92FS "UNITED WE STAND"
M1A National Match





http://www.thesabregroup.com
http://www.blueyscustomalloys.com



Jacobite
Moderator



USA
6102 Posts
Posted - 02/10/2005 : 8:00:35 PM
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That is what I have been thinking Mecha. Don't worry KA will show up sometime.

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Don Nelson:

Git-R-Done!





runtz
Starting Member



USA
1 Posts
Posted - 02/14/2006 : 08:05:52 AM
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Hi I was wondering is this a ground bolt? it looks a little diffrent than the example pic but it dosent look original either? If so where can i find a replacement?

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ADjam5
Starting Member



USA
6 Posts
Posted - 03/16/2006 : 2:39:39 PM
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How are they allowed to sell guns with a flaw like this?
Its like putting heavier oil in a car to stop the lifters from tapping, just so you can sell the car.

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NYSRPA member
NRA member
Lifetime NAHC member


jklinstein
Gunboards Member



USA
20 Posts
Posted - 07/25/2006 : 11:48:05 AM
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My bolt head looked ground, but the edges were still rounded. I think the critical factor is bolt length as noted by Dr. Zero. My bolt length is 1.820, which means it's .015 shorter than an average new bolt - so I think it's ground even though the edges are rounded.


Drakejake
Gunboards Member



89 Posts
Posted - 10/09/2006 : 12:53:00 PM
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My bolt has slight rounding on the sides. Is this the chamfering? I do not have a micrometer and so cannot measure the bolt. The bolt gap is .010. Fired cases show no bulges or other problems. Rifle works perfectly.

Thanks,

Drakejake


Dr Zero
Moderator



USA
2694 Posts
Posted - 10/09/2006 : 1:17:20 PM
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quote:
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Originally posted by Drakejake

My bolt has slight rounding on the sides. Is this the chamfering? I do not have a micrometer and so cannot measure the bolt. The bolt gap is .010. Fired cases show no bulges or other problems. Rifle works perfectly.

Thanks,

Drakejake

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Its kinda hard to tell without a pic but if you can take the bolt head off and stop by some place like NAPA or a machine shop and they can measure it for you to be sure.


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www.drzero.org/coa
The Original CETME manual's Free for DL at www.drzero.org/cetme
Along with G3 manual's and now 21 AK and SKS manuals


Drakejake
Gunboards Member



89 Posts
Posted - 10/09/2006 : 4:27:12 PM
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OK, I just bought digital calipers at an auto parts store. The bolt measures about 1.816. What's the verdict?

I take it this is .015 to .02 short. What's the problem or danger?

Thanks,

Drakejake


Dr Zero
Moderator



USA
2694 Posts
Posted - 10/09/2006 : 6:27:59 PM
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quote:
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Originally posted by Drakejake

OK, I just bought digital calipers at an auto parts store. The bolt measures about 1.816. What's the verdict?

I take it this is .015 to .02 short. What's the problem or danger?

Thanks,

Drakejake

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What difference does a Ground Bolt make?

It mask the fact that the parts are worn out.
Its not the grinding of the bolt head thats important to all of this, its the fact that the parts are worn out and need replaced and when hacker arms grinds the bolt head, it takes away your ability to gauge the wear of the other parts. THATS the dangerous part

If it was me I would get a new bolt head a new locking piece and order some +4 rollers and just rehab the whole system and then you would have years of enjoyment and not be wondering about wear.

That is just my opinion on what I would do in the same situation.


--------------------------------------------------------------------------------

www.drzero.org/coa
The Original CETME manual's Free for DL at www.drzero.org/cetme
Along with G3 manual's and now 21 AK and SKS manuals


Drakejake
Gunboards Member



89 Posts
Posted - 10/09/2006 : 11:59:04 PM
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Would getting an unground bolt eliminate my current .010 bolt gap, or would the plus 4 rollers take care of that issue? Will these renovations require the barrel to be "repressed?" Bottom line: my rifle has too much headspace, the case is not adequately supported, and the rifle is dangerous to fire? How can Century get away with faking correct headspace and selling dangerous firearms? Does anyone know how many blow-ups have been caused by excessive headspace in Cetmes?

Thanks,

Drakejake

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Edited by - Drakejake on 10/10/2006 01:02:57 AM


Drakejake
Gunboards Member



89 Posts
Posted - 10/10/2006 : 11:26:16 AM
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WHAT CENTURY JUST TOLD ME:

My bolt head measures 1.816. Century's minimum spec is 1.825. I talked to their 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 set from Makarov.com.

Thanks for your information and advice,

Drakejake

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Edited by - Drakejake on 10/10/2006 11:39:27 AM


Dr Zero
Moderator



USA
2694 Posts
Posted - 10/10/2006 : 6:40:45 PM
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When you get the whole bolt carrier try swapping out the parts first the bolt carrier may be too long to be a direct drop in.

Sounds like you are on the right track keep us posted and we will be happy to help!



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www.drzero.org/coa
The Original CETME manual's Free for DL at www.drzero.org/cetme
Along with G3 manual's and now 21 AK and SKS manuals


Drakejake
Gunboards Member



89 Posts
Posted - 10/11/2006 : 2:31:09 PM
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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. Comments?

Drakejake


Drakejake
Gunboards Member



89 Posts
Posted - 10/12/2006 : 11:46:47 AM
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MY PLAN:

When I get the new 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


Dr Zero
Moderator



USA
2694 Posts
Posted - 10/12/2006 : 6:50:28 PM
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quote:
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Originally posted by Drakejake

MY PLAN:

When I get the new 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

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Before you try that measure the length of the carriers if its a tad long it will bottom out in the charging handle cup and will give you a false reading and may not lock up at all.
Try swapping bolt heads and locking pieces to get the best measurement on the old carrier and there where you stand.


--------------------------------------------------------------------------------

www.drzero.org/coa
The Original CETME manual's Free for DL at www.drzero.org/cetme
Along with G3 manual's and now 21 AK and SKS manuals


Drakejake
Gunboards Member



89 Posts
Posted - 10/13/2006 : 12:49:33 AM
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OK, will do.

Drakejake


Drakejake
Gunboards Member



89 Posts
Posted - 10/14/2006 : 5:38:28 PM
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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


Dr Zero
Moderator



USA
2694 Posts
Posted - 10/14/2006 : 10:09:56 PM
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Try a new locking piece and some +4 and it might put you in spec the locking piece can make a big difference if the other is getting worn.
Check with arnaiz in spain he sells them or ask shari he might have one

--------------------------------------------------------------------------------

www.drzero.org/coa
The Original CETME manual's Free for DL at www.drzero.org/cetme
Along with G3 manual's and now 21 AK and SKS manuals


Drakejake
Gunboards Member



89 Posts
Posted - 10/15/2006 : 01:24:47 AM
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But I tried an unused locking piece--no wear at all.

Thanks,

Drakejake


Dr Zero
Moderator



USA
2694 Posts
Posted - 10/15/2006 : 11:26:13 AM
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quote:
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Originally posted by Drakejake

But I tried an unused locking piece--no wear at all.

Thanks,

Drakejake

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Put all the original parts back in there and do what Century asked and send it back to them for the warranty work seems to be the least expensive all the way around.

--------------------------------------------------------------------------------

www.drzero.org/coa
The Original CETME manual's Free for DL at www.drzero.org/cetme
Along with G3 manual's and now 21 AK and SKS manuals


Drakejake
Gunboards Member



89 Posts
Posted - 10/15/2006 : 2:11:33 PM
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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?

People have stated that Century may confiscate the rifle as unrepairable and offer the wholesale value (c. $200) as reimbursement. I can't risk that.

Drakejake


Dr Zero
Moderator



USA
2694 Posts
Posted - 10/15/2006 : 4:51:46 PM
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I would try century, I have heard of them keeping one rifle so far I have heard them sending out whole replacement rifles also.


--------------------------------------------------------------------------------

www.drzero.org/coa
The Original CETME manual's Free for DL at www.drzero.org/cetme
Along with G3 manual's and now 21 AK and SKS manuals


Drakejake
Gunboards Member



89 Posts
Posted - 11/10/2006 : 5:58:50 PM
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I have now gotten a supply of new parts and went to work today. Here is my report on the Cetme with ground bolt and .010 bolt gap:

I tried an unground bolt, new locking piece, and plus four rollers--no bolt gap (.004 wouldn't go in; this is my smallest). Putting plus four rollers into the ground bolt and combining this with a new locking piece gave me a gap of about .015. Perhaps Century had already installed plus fours and I got an incorrect reading with my digital calipers. Maybe we now know why Century ground the bolt: this was the only way to get a bolt gap without repressing the barrel. Century has claimed that bolt grinding is a method of setting headspace approved by a Spanish armory manual of 1975. No one seems to have been able to confirm Century's statement.

I also have a Cetme with an unground bolt and no bolt gap. With plus four rollers and a new locking piece, I got a gap of about .013. So I should be good to go with this one. Next I will take the two Cetmes out to the range to see if they still work with the new parts.

Drakejake


jfowl31
Gunboards.Com Silver Star Member



USA
713 Posts
Posted - 12/01/2006 : 11:37:32 PM
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Since this is a sticky, I feel I need to reply to it so that newbies dont read it and think that what Drakejake did was acceptable by any means. Heres why its unsafe... in addition to masking wear.

Bolt Gap is a measurement which indicates where the rollers are along the locking piece. a high Bolt gap means that the rifle will unlock very fast, as the rifle is just barely into battery, and the gap is left wide open. a low bolt gap means the rifle is well into battery, will take more time to unlock, chamber pressures will be slightly higher, recoil will be less as more pressure is used to unlock the bolt. a bolt gap out of spec on the high end doesnt allow the bolt to sufficiently lock into battery, which eans HIGH recoil, and very fast wearing of parts. Out of spec BG on the low end means that the timing is too slow, and pressures get too high in the chamber, which is why case head separations are common with low BG's... the high pressure is unsafe obviously, and an explosion COULD happen over time as the chamber wears... you get the point.

The REASON grinding a bolt is BAD: It masks the fact that parts are out of spec/worn. By grinding the bolt head, it allows the gap to be bigger, but doesnt not change anything about the timing of the rifles system. All it does is allow a feeler guage to go between the carrier and bolt, the rollers are still in the same place along the LP because the material was taken off the back end of the bolt.

The reason it doesnt change anything about the timing is THIS: The Cetme bolt design does NOT head space like a normal rifle. in fact it doesnt really headspace at all. the bolt face is tight up against the chamber EVERY time, so the headspace is the same EVERY time. technically there is no Headspace on a Cetme or HK. Its just a chamber with a bolt face up against it. changing you bolt gap doesnt change headspace because there is no headspace. changing your Bolt gap changes where the rollers are along the locking piece. Since the bolt is in the same position Every Single time it slams home, the rollers are in the same place as well since they are always the same distance off the bolt face. Adding larger rollers changes bolt gap because they are larger therefor they dont have to press out as far to reach the walls on the trunnion, which makes the locking piece not be able to wedge as far between them so the gap is larger. adding a new locking piece gets rid of worn spots in the old locking piece which does not allow it to wedge as deep into the bolt head, thus increasing boltgap. replacing a worn bolt head reduces slop created by the rollers pressing hard against the walls of the slots which they come out of, which can allow the LP to slide further between them, which reduces bolt gap, so replacing with a new one increases gap.

The main thing to see is THIS: bolt gap is not important because its a gap... its not a cushion of gap which most people think at first sight... bolt gap is a measurement that tells you what stage the bolt group is in. By grinding the back of the bolt, a false measurement is given. It makes it seem as though a rifle is in spec when actually grinding the back of the bolt does nothing to change anything about the rifle except how big of a gap is between the bolt and carrier.

Hopefully this will help out others who come to the form, and read the stickies.

Drakejake was convinced that his rifle was safe, and thats his choice, because its his rifle and his face if it ever does finally wear out enough to explode. But there is a reason that manuals, Cetme armories, and HK experts/gunsmiths/armories all give the same information on how to alter bolt gap. And doesnt it seem a little odd that Century Arms is the only ones who say its ok to grind a bolt...............

If you have a ground bolt, you are not required to get a new one. You can measure it, and compare it to the nominal bolt head length of 1.835". If your bolt measures 1.827", you need to subtract .008" from your bolt gap reading to get an "actual" bolt gap. so if your bolt measures 1.827", your new "spec" for bolt gap is .012" to .028".

If anyone has any questions about how to fix or attack a problem or has any questions on how to check anything on these rifles, PLEASE start a thread and ask your question. And dont be discouraged and think that its going to be "multiple hundreds" of dollars to fix. Most problems are easily fixed on these rifles at a very low cost. Good luck and Happy Shooting to you all.
 
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