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Thread: CETME woes

  1. #1
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    CETME woes

    First post, been lurking for awhile reading hours upon hours here and I've learned quite a bit. Just wanted to throw out some concerns on a newly acquired CETME.

    I purchased a CETME from a not so local shop. I had been looking for a wood furniture surplus looking CETME for some time. I even bought a parts kit from SARCO with the intention of building one, learning along the way, kind of a winter project. Anyways, one came up and the price was right so I got it.

    After a good cleaning I loaded a mag and hit the range. First shot locked the gun up. It did not cycle, extract, nor eject the brass and I couldn't cock the rifle. With a block of wood and a smaller hammer, I tapped the charging handle back to retrieve the brass. The case mouth looked like a torx bit and the brass itself had obviously floated into the flutes leaving defined, raised lines down the first third of the case.

    After some reading, I cleaned the chamber some more, cycled the rifle manually about a hundred times and headed back to the range. I loaded another magazine. This time the rifle fired 3/5 times and when retrieving the brass for inspection, I found that I had a case head separation. Luckily the front half of the case was not stuck in the chamber. After that, I decided to do some more reading.

    So, checking things over, one of my concerns was the ammo. I had used my reloads that I use in my M14/FAL's etc just a plain jane 150gr FMJBT loaded in LC brass with CCI #34 primers doing 2,600fps

    This particular batch according to my records was on its 3rd loading. For a rifle that is notoriously hard on brass, maybe I should stick to once fired or just factory rolled?

    Bolt gap. I didn't even know what bolt gap was until I started reading here. But in checking my bolt gap, ,I had .002 bolt gap. The rifle locks up fine, cocks fine and at first impression seems OK.

    I took my bolt from my parts kit and tried it for grins and now have a bolt gap of .009. Is this OK? Does this affect my headspace? I'm still learning the nuances and characteristics of DRB rifles so please excuse my ignorance here.

    Inspection of the bolt, bolt carrier and locking piece all look like typical lightly used parts. They don't look brand new with a fresh parkerizing, but not worn down chrome either. Best I can tell is that neither of my bolts have been ground down. The rearward portion of my bolt heads are chamfered and have what looks to be OEM finishing on them.

    I tried to measure the cocking tube gap from the information provided in the sticky written up by bladerunner(?) but the pictures are gone and not being 100% on the nomenclature of the parts I cant be certain, but I think its good based on the writings of what and how the cocking action should feel like. The handle comes out about 1/2" and engages, then retracting the handle to 90 degrees unlocks the bolt without any unusual force.

    So, sorry for the wall of text here fellas, just excited to find a place with so much knowledge.

    My questions are:
    1. Does changing a bolt to achieve proper bolt gap affect anything negatively

    2. What else should I be looking for

    3. Are these rifles that sensitive to ammo? Ive heard some will chew through anything, and others saying only run commercial 7.62x51 through them.

    Thanks for your time in advance, really looking forward to learning more and getting this rifle safely up and running.

    r/ Stape

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    holescreek's Avatar
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    Bolt gap. I didn't even know what bolt gap was until I started reading here. But in checking my bolt gap, ,I had .002 bolt gap. The rifle locks up fine, cocks fine and at first impression seems OK.
    The spec for bolt gap is .004"~.020". Assuming (at this point) your barrel isn't loose, you can compensate for worn parts by putting larger diameter rollers in the bolt head. You'd need to remove your existing rollers to see what size you have now to know what you need to buy.

    the lever on your carrier that holds the bolt has a ramp on it that rides on a ramp on your bolt head. The bolt gap spec is what it takes to keep the two parts in the proper place to work together.
    The fact that you're down to a .002 as purchased, and got a .009 with another BCG suggests the original parts are pretty worn. There are specific areas to check including the locking piece shoulder angle, the front window of the bolt head where the roller rests when locked in place, and the face of the carrier where the locking piece skirt rests.

    This particular batch according to my records was on its 3rd loading. For a rifle that is notoriously hard on brass, maybe I should stick to once fired or just factory rolled?
    These rifles eat anything but soft brass. When troubleshooting, steel case is preferred to eliminate issues with chamber flutes. If you have bad flutes, even steel case won't extract. I've reloaded brass from my Cetme's over a dozen times, the exterior flute marks on the brass don't cause problems for me.

    There will be lots of questions until you get it running correctly and we're going to need clear focused photos to make decisions on where to look next.

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    Much appreciated info Sir. To be exact, I swapped the bolt head only, to achieve the .009 bolt gap. I haven't fired it yet with this new(er) bolt, but would that be ill advised? If you could explain what you need a picture of, I'll take them tonight and post em up. I'll also take out the rollers and measure them. What other measurements could I take that would be helpful?

    Thank You.

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    holescreek's Avatar
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    A common problem with older CAI built Cetmes is the barrel being loose enough that they get jack hammered forward into the trunnion. Even when pounded flush with the trunnion rim the rifles will still function, but once the barrel shifts below the trunnion rim the headspace goes long and your brass will stretch.
    Headspace in these rifles is set when the chamber is cut by setting the amount of cartridge brass (or go gauge) standing proud of the barrel face. The typical amount of stickout is around .128" and is determined by measuring the depth of the bolt face counterbore and adding .009" so there is an air gap between the bolt face and barrel face when a cartridge is in the chamber.

    Typically I like to see a clear image of the bolt face to see if it's been striking the trunnion rim and if possible a photo taken through the rear of the receiver of the barrel face. A pic of the front window of the bolt head and locking piece shoulder are sometimes necessary, but we're not there yet.

    Cetme parts are completely interchangeable because these were military weapons. Swapping parts is fine as long as the rifle was built correctly, mainly that the cocking tube was properly placed for cocking tube gap prior to welding. If it was set too short, the carrier will strike the cocking handle support with each firing and eventually break the tube off of the receiver. The majority of CAI guns seem to be OK, but we've had a few pass through this site in the last 10 years with visible cracks on the joint. Typically if the rifle cocks fine it's going to be OK.

    A quick check for cocking tube gap is to slap the bolt home then try sliding the cocking handle and support fore and aft inside the cocking tube. If it moves freely a little bit, there is a gap and everything is fine. I'll post some samples of pics I have stored on this site.

    Here's a pic of where the bolt head is striking the trunnion rim:
    2v2JfBipVxAjwmD.jpg

    Worn bolt head window front:
    20170401_151606_zpseuxurk0d.jpg

    Locking piece shoulder angle
    20170401_153653_zpsxvnppe7e.jpg

  5. #5
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    rps20191106_170559.jpg

    rps20191106_170658.jpg

    rps20191106_170739.jpg

    rps20191106_170829.jpg

    Tried to get the clearest pics possible with a phone, then had to reduce them. Man, I'm telling ya, successfully loading photos for me is like performing the first brain transplant, pretty excited lol.

    ETA: my rollers measure out at .314, this and the pics above was the configuration that gave me a bolt gap of .002
    Last edited by Stape; 11-06-2019 at 07:02 PM.

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    The good news is you're not on the trunnion rim, so it's just a matter of getting some new rollers. I can't see any detail in your photos of the bolt window and LP shoulder.

    8mm rollers are standard and are considered "Zero". There are "plus" sizes larger and "minus" sizes lower, designated as +2, +4 ,..., and -2, -4, ... A +2 roller measures 8.02mm, a +4 measures 8.04mm. If you're starting at .314" you should have -2's in place now. I'd start with a pair of +8 rollers if that's the case.

    On the other hand, you can just run your better bolt head for awhile and see how it shoots. That way if you need to buy more parts you can just order rollers for the "bad" bolt head then and save on shipping cost.
    Last edited by holescreek; 11-06-2019 at 08:35 PM.

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    Awesome sauce man. I'll start there.

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    rps20191106_193949.jpgrps20191106_193839.jpg

    Maybe these might help too?

    Just to be clear... Shoot my better bolt head, the one that measures in at .009, as opposed to putting rollers in my out of spec bolt head that measured .002? Either way I'd like to get more range of leeway and not run so close to min-max tolerances. So shoot my better bolt head and see what's up, and soon order new rollers to get it to where it needs to be ideally?
    Last edited by Stape; 11-06-2019 at 08:45 PM.

  9. #9
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    Your better bolt head will be fine, just check your bolt gap about every 200 rounds. If it doesn't change after 400 rounds, don't worry about it.

    If later on you decide to buy rollers for your better bolt head, measure the rollers it has and order a pair at least two sizes larger. Your bolt gap will grow by around .0023" for each size increase. .016" is the gap size that many consider "the sweet spot". When your gap opens up to the higher end of the tolerance (.020") the rifle unlocks too easily and recoil gets dodgy.


    Here's a good photo of a very worn locking piece. You can see the long divot on the left side of the shoulder:
    worn stuff 005.jpg
    Last edited by holescreek; 11-06-2019 at 09:31 PM.

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    Would a new locking piece be a good idea as well? They seem cheap enough and if I'm ordering rollers anyways it seems like a good thing to have.

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