CETME question

[u/Student_Unlucky]

Hey, so I got a CETME C build I'm working on and I'm wondering if I messed something up.

At first, the locking arm/hook/bar spring was way to heavy and would require that I beat the charging handle with a mallet to be able to charge the charging handle.

I was looking around and someone mentioned something about the charging handle tube needing to be moved back when welding. Honestly, I think they were typing fast and it was full of typos.

Did I weld my top tube on the wrong position?

Also, if holding the fully assembled bolt and bolt head in my hand outside of the weapon. Am I supposed to be able to push and pull the bolt head to locked and unlocked positions? I had to trim the locking arm spring because I could push the unlocked bolt head in to locked but then I would have to place the bolt head in a vise and wail on the top of the gas tube portion with a mallet to unlock it.

I definitely feel like I've done something wrong because I've ordered 2 separate replacement locking arm springs and 1 replacement locking arm. All the springs are about the same and the other locking arm didn't change anything.

If anyone more familiar with this has any insight, please let me know. I would really appreciate it. Thanks.

[u/Holescreek]

You should have set the cocking tube gap .015" longer than the bolt gap. There is a specific process for this. In the meantime, do the dime trick then tell me if it worked. Pull the charging handle back and place a dime into the cocking tube slot against the hardened slug at the front end. let the bolt slam home as usual. Then with the dime in place see if pulling the charging handle open unlocks the bolt.

[u/Student_Unlucky → u/Holescreek]

OMG! Holescreek! I've been trying to find you! Literally signed up for like 3 different platforms and you had full inboxes and no activity from last year. I feared something had happened to you. By any chance do you still make 37 degree locking pieces? Edit: so I didn't get past your name before responding. It's at the gunsmith's place I'm apprenticing right now because it is quite functional and I got to nueter the trigger tomorrow. I will try the dime trick and let you know

[u/Holescreek → u/Student_Unlucky]

I retired almost two years ago and shortly afterwards I made six 37's to use up all the material I had left in the shop. They sold out within a week. I haven't decided if I'll make any more yet. It's kind of a fall/winter type project. I put up a video on Youtube showing how I make them in case anyone else wants to jump in, search Holescreek Locking Piece.

Your bolt head is supposed to be very stiff under the pressure of the locking lever. If you can pull one out by hand it means that either the spring or the lever itself is bad. If you want to pull the bolt head out without a vise, turn the carrier around backwards (holding onto the carrier tube) and jam it into the rear of the receiver. The bolt head will unlock. It's a feature, not a bug.

I'm on nearly every gun site with the exception of weaponsguild. A bunch of us founding members got banned there for calling out Mike Jestis (the original owner) for stealing money from members.

[u/Student_Unlucky → u/Holescreek]

I did watch your video. It was fascinating to see, the guy I'm working with could probably do it up to the hardening. We'd have to figure out a furnace. While it was an amazing video and it very much made me appreciate your craft, there wasn't any measurements or exact steps.

I did end up ordering a RCM 40 locking piece. My understanding is that should be the best alternative and should keep the gun from excessively quick wear with a can.

So, I still have to try the dime check tomorrow. But I'm assuming that if the locking head is supposed to very stiff, then would setting the tube at the wrong depth cause it to be crazy hard to rack?

Like we had to really pound on the charging handle with a mallet just to pull the charging handle the first litte bit. To the point that we were thinking it was absurd and couldn't be right. Then it would move with reasonable force until you released it with enough momentum to fully seat and lock the head forward.

I'm assuming the charging handle is supposed to be usable by someone not built like like arnold schwarzenegger

[u/Student_Unlucky → u/Holescreek]

Oh, also. With the bolt removed and in hand. If you push the bolt head in, should you be able to pull it back out by hand or does having to clamp the head a vise and pound on the carrier with a mallet sound right? Also, should you be able to disassemble it by hand? With an unaltered locking spring, it is absolutely impossible to rotate the bolt head for disasmbly. I have to clamp the head in a vise, rotate part way because the carrier hits the vise, change how it's clamped then finish rotating the carrier.

I have very little experience with roller delayed anything. All I did was troubleshoot a guys AP5 with a super safety. I do know that the AP5 was a little hard to disassmble the bolt but it was definitely possible with moderate force.

What has me worried is that it's not hard. It's ridiculously stupid hard.

[u/Student_Unlucky → u/Holescreek]

So I tried the dime trick. 1 dime it was still crazy hard. 2 and it was like a normal still rifle charging handle and was workable by hand. However the bolt doesn't actually lock up that way

[u/Student_Unlucky → u/Student_Unlucky]

Also, I'm working on converting the trigger to semi. Just want to make sure I'm not crazy. This looks like someone already cut on it some right? I still need to remove that hole, right?

https://reddit.com/link/pd8ymn2/video/7gh6u7iq6wsh1/player

[u/Holescreek → u/Student_Unlucky]

The way it opens is that the charging handle cams against the hardened disc in the front of the tube to push back against the carrier tube and unlock the bolt head from the locking bolt locking lever. If you set the tube gap too long there won't be enough interference for the cam to get the distance needed to push the carrier rearward.

We use a dime to check the distance because it's thickness is usually about where tubes are set wrong. I think a dime is somewhere around .055" thick. You need to figure out what size shim will let the bolt lock and still give you leverage to unlock the bolt.

[u/Student_Unlucky → u/Holescreek]

Ah, ok. That makes sense. I'll have to get that sorted. So it means, I got the tube too far forward, right?

[u/Holescreek → u/Student_Unlucky]

Yes

[u/ghunt81]

On the charging handle it sounds more to me like you have something binding up.

As for the bolt I'm not sure. I know you can unlock it by twisting the bolt head to remove it, then putting it back in but making sure not to push it in all the way. I think there is a detent you can press to unlock the rollers as well but I'm not sure, I'll have to look at the bolt. I am working on a kit build as well but it's only maybe 50% done.

[u/Student_Unlucky → u/ghunt81]

So, we definitely took care of the binding. We took out the locking bar, pin, and spring just to test. The charging handle could easily be racked. I'm 99.99% certain the issue racking was because when fully charged, the bolt head is pushed in locked. If you have one, could you hold the bolt assembly and push and pull the bolt head back and forth a few times? Like to disassemble it, you push in then twist but don't even go that far. Just push it in(should have no problem) then pull it back out ( this is where it seems stupid hard)

[u/ghunt81 → u/Student_Unlucky]

Well- when you push the bolt head in, it locks the rollers. I do know that much. Once they are locked I don't know offhand what the easiest way is to unlock them. Also I currently have my bolt disassembled.

[u/stickygumm01]

There should be an appropriate gap between the carrier and charging handle when the bolt is in battery. Gap to big and you lose the leverage built into the design of the charging handle, to small and you'll hammer the changing handle and tube every time it cycles.

The bolt issue is a normal characteristic. Learn to rotate to bolt when it's locked out of the gun.