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chas442
February 26, 2015, 18:48
I just acquired a used cetme built by Century. I need some advice on a repair. If this has been covered please point in the direction to find it. The rear tube that the butt stock takedown pins pass through in the receiver is separated on the right side. Has anyone had to deal with something like this? I have access to a mill, mig welder, gas welder and a tack welder.

Any and all help will be greatly appreciated.

21HK
February 27, 2015, 16:19
That little tube can be tacked to the inside of receiver, it acts a guide for the push pin.
You may get away with using a MIG but a TIG would be better...cleaner weld and no splatter.

Pull the stock off, remove the bolt and carrier assembly, insert the push pin to line up the tube and give it a quick tack. Depending on your welding skills you may want to substitute the pin with a copper rod, if you burn through the tube you'll end up welding the push pin in.

You may want to put some anti splatter on the inside of the receiver just in case... you don't want anything in there that could bind the bolt carrier.

You will more than likely end up with a burn mark on the outside of the receiver. You can touch it up if you want, once the stock goes on it will cover that.

chas442
March 03, 2015, 08:59
Thanks 21HK.
Do not have a tig but do have a mig. The Weld is a little sloppy. Had to do a little dremeling. Its ugly but functional. It started out as a Century so i'm not too concerned about interior appearance.

gunplumber
March 03, 2015, 09:24
It's indicative of overpressure - I'd do a close examination of the parts - sometimes the drunken monkeys and angry beavers at CAI set the bolt gap by grinding the back of the bolt. It also happens with a defective or no buffer - had a DOE 33 - non-buffered carrier & non-buffered stock. Sheared the rear of the receiver off at the pin holes. Made a replacment section from an uzi mag.

chas442
March 03, 2015, 17:20
Gunplumber you really hit nail on the head. The bolt is ground down to 1.822". I compared it to a non ground bolt head which measured 1.834".
The cocking tube gap is way to large. It is difficult to unlock the action unless I place a washer in the cocking tube. The gap is correct with the washer in place and the cocking lever lays flat on the nub on the tube.
The bolt gap is 0.013" but the bolt is ground approximately 0.012". That tells me that the actual bolt gap is 0.001".
Knowing or least suspecting 0.012" was ground off, can I address the bolt gap as a 0.001" gap. Can I install rollers that would bring the measured gap to 0.16" to 0.032" taking into account the 0.012" that was ground off) without making the rifle dangerous. The rollers are 8.05mm(sorry about mixing in metric).
What is the appropriate roller size to bring the bolt gap within spec?
What I would like to do is correct the bolt gap with appropriate rollers and then correct the cocking tube gap by tacking a washer/spacer at the front end of cocking tube. I would mark the bolt head as being 0.012" short for gap checking. I have a bad habit of keeping my guns forever.

Any help would be greatly appreciated

gunplumber
March 03, 2015, 17:25
Bolt gap first. RTG has oversize and undersize rollers, but you'll need a new bolt head.

The cocking handle extension is not worth the effort. You'd have to cut the cocking tube off and weld it back on - this is a critical dimension. End of extension to beginning of bolt carrier 0-.022 (box cutter blade) and the closer to zero the better. as long as it can wiggle.

Work around is just to solder a washer/build up end with weld (on the extension, not the carrier).

The opposite problem - not enough gap, causes it to (false) headspace off the cocking tube and usually will crack the tube.

Might be more cost-effective to part it out and buy a PTR, but it will be close.

chas442
March 04, 2015, 00:25
Is it necessary to replace the bolt head. I feel I know how much has been removed with grinding? it appears that the only requirement of bolt length is to be able to check gap. It doesn't appear to change the function of the rifle. It doesn't seem to have changed the function of the rifle other than splitting cases

chas442
March 04, 2015, 08:59
Ordered a bolt head from apex.

gunplumber
March 04, 2015, 09:35
I don't know if it's a safety issue.

I speculate that the firing pin depth would be increased possibly causing pierced primers.


But I'm not sure it won't.

chas442
March 04, 2015, 11:53
My thinking is this and please correct me if I'm wrong. The area that was ground never makes contact with the adjacent flat of the carrier. The distance the firing pin travels remains unaltered.

On a side note. What size rollers would you recommend using to increase bolt gap from 0.001 to 0.011-0.016

chas442
March 04, 2015, 11:54
Existing rollers are 8.05mm

gunplumber
March 04, 2015, 12:06
I really don't know on the bolt. I'm not comfortable reusing it, but I can't articulate why.


Do they have any marks on the top? A standard is 8mm. An 8.04mm (two lines) is a +4. If it's already a +4 (largest factory) you may have to go to an aftermarket +8/+10.

http://www.robertrtg.com/store/pc/showsearchresults.asp?pageStyle=H&resultCnt=32&keyword=HK+roller

chas442
March 04, 2015, 12:22
current rollers Have 2 lines etched on flat

chas442
March 04, 2015, 12:27
I've got a replacement bolt head ordered. I will recheck bolt gap when it arrives. I will then get bolt gap within spec. Then I'll try to deal with Cocking tube gap.

Thanks for your help.

gunplumber
March 04, 2015, 12:31
Those are already +4 (8.04mm).

You can try the aftermarket ones linked above, but your headspace is way off.

It's a nightmare, but you may need to pull the sling mount, triple frame, and barrel. Rotate barrel 180, and press it back in for a bolt gap of .118". Remount tripple frame and pin with sling mount.

But how can you measure the bolt gap with the back of the bolt ground? That's why, even if the ground bolt itself isn't dangerous, you have no way of knowing what it should be.

I suppose you could measure a spec bolt, and subtract your bolt measurement, then subtract the difference from your measured bolt gap.

chas442
March 04, 2015, 17:08
I've Researched on other sites and they would indicate that a new bolt is 1.835" in length. My other rifle Has an unground bolt length of 1.834". This gives me a bit of confidence that approximately 0.013" was ground off the bolt head.
I plan looking deeper on whether the firing pin protrusion may be increased due to the Grinding.
As a side note, I did put 3 rounds of milsurp 7.62x51 thru this rifle before the action could not be opened. In hindsight that was caused by excessive gap at the cocking tube. I inspected the brass. No pierced primers and 1 case separation with nothing noticeable vented back at me.

gunplumber
March 04, 2015, 17:17
As a side note, I did put 3 rounds of milsurp 7.62x51 thru this rifle before the action could not be opened. In hindsight that was caused by excessive gap at the cocking tube.

The only thing the cocking handle extension gap would cause is difficulty in charging the rifle, as the rollers would not be fully unlocked when the handle is cammed outward.

No affect on firing it.

chas442
March 04, 2015, 20:16
GP I appreciate all your advice. Do you have any interest in hearing about future feedback on my progress? It'll be a week or so before I can do anything with bolt head gap.

gunplumber
March 04, 2015, 20:19
I'm subscribed to this thread.

chas442
March 05, 2015, 15:58
On a whim I swapped out the bolt and carrier from my CETME that is within specs. Bolt gap became 0.014 and cocking tube gap became 0.010. Rollers are also marked +4.
There may be more going on than just a ground bolt.
I will know more once the replacement bolt head comes in.

djfin
March 05, 2015, 16:26
Just my two cents but I have read on several sites that the bolt and carriers are not interchangeable between Cetme's and Hk rifles. RTG Parts used to have and interchange list but it is not on his site anymore. I would not fire that setup. If you are near the western burbs of Chicago you can contact me and we can check the bolt gap with my in spec HK bolt group ( New rollers and locking head) to see what you get. PM me if interested

chas442
March 05, 2015, 17:04
DJ
Thanks very much for the offer. I am going to wait for the replacement bolt head to come in.
Do you ever shoot at article 2 in Lombard? That is the indoor range of choice for me. I used to work for them part time back when they were Gun World in Bensenville.

gunplumber
March 05, 2015, 17:49
The CETME carrier extends into the handle extension - like a telescope. The HK carrier butts up against it's cocking handle extension. I don't know if the bolt heads and locking pieces interchange because I've never tried.

chas442
March 05, 2015, 18:32
It appears that the Trunnions, Bolt heads and carriers do not interchange between HK and CETME

21HK
March 05, 2015, 18:32
From RTG parts:

Cetme - HK G3 Compatibility page!
(are HK parts a match for your Cetme?)

YES, the below HK parts will work perfect on a Cetme
Barrels Yes
Barrel Retainer Pins Yes
Firing Pin Yes*
Spring, for firing pin Yes*
Rollers Yes
+2, +4 Rollers Yes
Retainer Plate and Roll Pin Retainer for Rollers Yes
Extractor Yes*
Extractor Spring Yes*
Recoil Spring Yes*
Backplate or Complete recoil Assembly Yes with minor fitting to the plastic sleeve at the end of the spring guide rod
Complete Stock set Yes with minor fitting to the plastic sleeve at the end of the spring guide rod
Collapsible Stock Yes with minor fitting to the plastic sleeve at the end of the spring guide rod
Buttstock Yes with minor fitting (needs the buffer hole matched to use the cetme buffer)
Grip Frames Yes
Complete Trigger Pack Yes (but no individual parts)
Rear Sight Yes (but only if entire sight base is swapped)
Handguards, Slim Yes
Handguards Wide Yes with minor fitting. Just like the old style HK triple frame, the cetme has a bipod retaining ring that prevents the wide from installing
Pistol Grip Yes
Triple Frames Yes
Flash Hider Yes
Eyeloop for triple frame Yes
Cocking Handle Yes*
Spring for cocking handle Yes*
Pivot Pin for cocking handle Yes
Mag Catch parts Yes
Paddle mag release Yes
End Cap, Dust Cover Yes (but cetme will not fit g3)
Bayonet Adapter Yes*
Bayonet Yes* (only when using adapter)
Retainer Pins Yes*
Blank Firing Adapter Yes
Claw, Stanag Scope Mount Yes
POF Carry handle and Port Buffer Yes (carry handle slight modification to cetme handguard)

*these items not only interchange but are an improvement over existing Cetme parts. Over the years some items have been strengthened or improved by HK.

No, the below HK parts will not work on a Cetme:
Trunions No
Bolt Carriers No
Locking Lever for bolt carrier No
Bolt Head No
Locking Piece No
Cocking Tube No
Support for Cocking Handle No
Recoil Buffer No unless using HK buttstock
individual fire control group parts like trigger, sear, hammer: No

21HK
March 05, 2015, 18:33
chase, you got me by a second or two:wink:

chas442
March 05, 2015, 18:40
It looks like HK changed the design of the trunnion which would require a bolt head change. I've seen receiver flats that would work for CETMEs HKs and PTRs.

chas442
March 05, 2015, 18:41
Damn. We're responsive

djfin
March 06, 2015, 11:10
DJ
Thanks very much for the offer. I am going to wait for the replacement bolt head to come in.
Do you ever shoot at article 2 in Lombard? That is the indoor range of choice for me. I used to work for them part time back when they were Gun World in Bensenville.

While my shop is only about 15 minutes from them I have not shot at Article 2 yet. I do most of my shooting on the weekends near Galena

chas442
March 07, 2015, 19:02
DJ
I'm not familiar with the Galena area. What range is out there? Public or private? Distances?

chas442
March 16, 2015, 11:06
I installed the replacement bolt head today. It came with standard rollers. I checked bolt gap and there was none. I installed the +2 rollers from the original bolt head and the gap came up to0.004". It is within specs but the cocking tube gap is too small. Can I use +10 and still stay within specs? I prefer to be at the upper edge as that will allow for future wear. I am hoping that the increase in bolt gap will also give me more of a cocking tube gap.

chas442
March 16, 2015, 11:09
Will increasing bolt gap have any affect on cocking tube gap since there is a 0.004" gap now?

gunplumber
March 16, 2015, 12:08
I don't have a spec for cocking tube gap, but from experience; if you can wiggle the handle and make the cocking handle extension move freely, it's fine (and ideal).

If it is larger than 0.5mm (test with a .022" box cutter blade) you may have problems.

If it is less than 0, you will get a flase bolt-gap reading and eventually the weld on the cocking tube at the receiver, will crack. The cocking handle extension is now the impact surface of the bolt carrier returning.

In this case, the closer to zero, without reaching zero, the more unlocking occurs when camming the handle outward.

Too much, and camming the handle outward does not completely unlock the rollers and causes the retraction of the bolt carrier to be difficult.

On bolt gap, the spec is 0.1 (.004") to 0.5mm (.020"). The larger the gap without going over 0.5 mm, the lower the unlocking force on recoil.

One of these days, I'd like to document the amount of bolt gap increase for each .02mm increase in the locking rollers. From thinking about it (but not testing it), I figure a .02mm diameter change in the roller would equate to a radius of .01mm, and therefore a +10 will increase it by .05mm. But I'm not positive that it is a direct correlation.

As I mentioned before, changing the cocking handle gap to make it smaller is major surgery, and to do it correctly, the cocking handle tube has to be cut off and rewelded. The work-around is to weld up, or solder a washer, to the relatively cheap extension ($10?). Likewise, the extension can be shortened slightly if you have no gap. When I do this, I mark the extension to signify that it has been modified. Just so 20 years down the road, there is no confusion.

chas442
March 16, 2015, 23:05
Now that I have a bolt gap of 0.004"with +2 rollers, I have ordered +8 rollers to increase the gap to hopefully bring Bolt gap to the teens. Then I'll tackle cocking tube gap.

djfin
March 18, 2015, 17:03
DJ
I'm not familiar with the Galena area. What range is out there? Public or private? Distances?

I shoot on my own land just outside of Stockton. I have backstops at 100,200 and three hundred yards. There is a public range just outside of Mount Carol that just reopened after being closed for a couple of years. They have ranges up to a 1000 yards with moving targets. I am looking for the flier for the name. I will post it when I find it.

chas442
March 18, 2015, 20:38
DJ

thanks for info

chas442
March 20, 2015, 10:09
I think I finally understand how a delayed roller weapon works. I give credit to bladeworks123 at militaryfirearm.com . He has posted some diagrams that really cleared up a lot of questions that I had. The link is http://www.militaryfirearm.com/Forum/showthread.php?14941-Delayed-Roller-Blowback-Understanding-Actions-Gap-and-Ammo. It will be necessary to have an account to view the illustrations. I hope that it is not a violation of forum rules to reference another forum.

chas442
March 23, 2015, 14:49
Installed the +8 rollers today. I now have 0.010" bolt gap. I replaced +4 rollers that produced a 0.004" bolt gap. Now that bolt gap is in spec I have to deal with Cocking tube gap. I used a gauge from an old carburetor gauge set that has pins starting at 0.005" and goes up in 0.005" increments. I now have 0.035" cocking tube gap. Can't cycle the action without tapping on the cocking lever. I'm planning on welding a bead onto the muzzle end of the tube portion of the carrier and grinding till I get the 0.010" bolt head gap and then grinding 0.020" more off for clearance. Would it be better to gring 0.015" to keep it close to Bolt head gap? I wanted to check here to see if this is a good Idea.
I have access to a digital caliper that measures up to 2 feet so I can get a good read on how much I'm taking off.

chas442
March 24, 2015, 08:32
GP
I just reread your earlier post. I am going to shoot for a 0.011 cocking tube gap. This rifle has very few rounds thru it. There may be some "settling". I'm going to make my adjustments, if it seems like a good idea, and shooting 100 to 200 rounds. I will bring a set of feeler gauges to make sure that the bolt gap doesn't go to zero.

chas442
March 26, 2015, 14:55
Put a bead on the muzzle end of the Bolt carrier. Ground the weld till the Bolt gap came back to 0.010". Continued till I have 0.015 to 0.020" cocking tube gap. Cold blued all the bare metal. There is approximately 1/2" opening at the cocking handle before resistance is noted. Cycles by hand now. I think I'm ready for test firing.

gunplumber
March 26, 2015, 15:07
Put a bead on the $5 cocking handle extension, not the muzzle end of the $125 Bolt carrier. Ground the weld till the Bolt gap came back to 0.010". Continued till I have 0.015 to 0.020" cocking tube gap. Cold blued all the bare metal. There is approximately 1/2" opening at the cocking handle before resistance is noted. Cycles by hand now. I think I'm ready for test firing.

FIFY

chas442
March 26, 2015, 20:15
Where exactly should I put the weld. Excuse my ignorance, but what is the cocking handle extension?

chas442
March 26, 2015, 20:32
I am dealing with a CETME not a G3. The carrier extends into the cocking handle support. The bolt carrier was already shortened. There was no bevel on the leading edge.

chas442
March 26, 2015, 21:13
What does FIFY supposed to mean?

gunplumber
March 27, 2015, 08:57
FIFY = Fixed It For You, as in - I altered your quote.


The part the cocking handle pivots against is the cocking handle extension - a cheaper part to modify. But since you've carrier is already altered, there is no value in it to destroy, so never mind.

chas442
March 27, 2015, 15:32
GP
Thanks for all your input. I just wanted to make this thing work safely without investing a lot of money. I'll update this thread when I've had chance to test fire and recheck gaps.

chas442
April 10, 2015, 18:08
Just got back from the range. Functioned flawlessly. Recoil was not unpleasant but I was using downloaded Indian "junk" ammo. Able to charge rifle with "normal" effort.
Will check clearances on Monday.

chas442
April 15, 2015, 19:15
Shot about 150 rounds at Range. Cleaned rifle. Bolt gap measured 0.009". Cocking tube gap is between 0.015" and 0.020". It seems like I have it fixed. Plan on taking it out again sunday and run another 100 rounds thru it and remeasure.

chas442
April 22, 2015, 22:05
Shot another 75 rounds. Cleaned the snot out of it. Bolt gap using a 0.009" feeler gauge is loose and at .010" seems a little tight. Happy with results.