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Thread: Cetme L build planning

  1. #171
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    Looking good! Keep the pics coming.
    14EH AIT Instructor-PATRIOT Fire Control Enhanced Operator/Maintainer

  2. #172
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    So after test assembly, the rifle will not go into battery with the trigger group installed. It seems the ejector is putting too much upward pressure on the bolt carrier, and it hangs if you bring it all the way back.

    Second problem is feeding from the magazine. I didn't heed Holescreek's warning and the feed chamfer on the rear of the barrel is just a tiny bit too small, or the feed ramp on the trunnion is a tiny bit too wide. About 25% of cartridges feed correctly, most just ram into the edge of the chamber and stuff the bullet back down the casing. Once the cartridge is shortened, they usually feed ok.

    Seeing as the barrel is at the bottom of a deep dark hole, and it is NOT coming out, I plan to use a countersink on the end of a drill extension and turn it with a tap handle to open up the chamfer on the barrel. It will take very little more to get it feeding properly, but I worry about having toouch unsupported chamber.

    On a positive note, by single-feeding it, it does fire and cycle the action with fairly mild recoil!

  3. #173
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    Quote Originally Posted by Xnke View Post
    On a positive note, by single-feeding it, it does fire and cycle the action with fairly mild recoil!
    That's a good thing!
    14EH AIT Instructor-PATRIOT Fire Control Enhanced Operator/Maintainer

  4. #174
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    I gotta admit that your comment about the Ls having small chamfers concerned me, but not having seen one in person I wasn't in a position to press the issue. The Cs have a 120 degree chamfer 5/8" in diameter around the chamber and a slight radius into it.
    Last edited by holescreek; 01-12-2019 at 08:59 PM.

  5. #175
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    Yeah, they have a pretty small chamfer from what I have seen. I've got an 82* countersink here, but I may need to make something 110-120 degrees to get this to work without weakening case head support.

  6. #176
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    Been working on this in between snow showers and other projects. I chamfered the rear of a stub barrel to see how deep the 82* countersink was going to cut before I got the diameter out large enough to fix the feed problem, and it's marginal at best. I think I have a 100* around here somewhere and I bet that would do the job. Shoulda done it in the lathe before I pressed it in place, but it is what it is. Just gotta fix it now.

    carrier sticking issue was solved with a cut down .308 case in the buttstock. Fixed that right up.

  7. #177
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    Slightly shallower is a lot better so a 120deg countersink would be best. Using the original gun as a guide is a bad idea....they had some serious issues with feeding. The magwell is floppy loose with STANAG mags and the original chamfer was very small and shallow. This means a lot bullets jammed into the back of the barrel stopping the action. You don't want to go too deep however so a flatter angle is going to help more. It doesn't take a lot to get the bullet sliding up the breech face into the bore instead of stopping and pushing the bullet into the case. You need to get the bullet to hit the chamfer though so go wide.

    If you are using the original mainspring you don't want anything behind the spring. The buffer spring works by having its rear platform sit against the stock while the mainspring coil binds and pushes the whole guide rod back against the front of the buffer spring. Its easier to visualize with a spring in your hand. If you don't have the right locking piece and bolt combo the buffer is really important. If you really don't have the right setup the buffer is critical. One of the biggest problems with these is the setup on the bolt. Excess velocity is a serious problem and the buffer spring is the only thing that will keep damage to a minimum. I'm not sure what the recoil of the 6.8 will do in this system but I guess you'll find out. If your carrier is binding in the receiver a set of spreader pliers is a big help.

    Hope something there helps. Keep up the program and let us know how its going.

    Frank
    Last edited by biffj; 01-22-2019 at 10:39 PM.

  8. #178
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    After building a LOOONG chamfer tool, I was able to cut a 110* chamfer in the back of the barrel and it feeds perfectly most of the time-but it acts like the recoil spring is not strong enough about half the time to fully strip a round out of the magazine. Shooting the rifle, it will fire, extract, and eject no problem. But there just isn't enough push forward to strip and lock forward on the next shot.

    In other areas, I'm looking at how to fit the handguard back in place, and this is where I'm at. I have no idea where that front handguard pin got to, but it's gone. Can't find another one either.



    The plan is to weld that front sight block to the end of the cocking tube, I'll build up the end of the cast steel sight block to close up the gap and neatly file it to fit snug, then weld the two together. The barrel band has been removed as the barrel diameter is 0.750 from just after the extended length trunnion, all the way up to the 5/8-24 threads on the last 1/2" of the muzzle.

  9. #179
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    It's been awhile so I just scanned back over the build from the beginning.

    On the missing pin, what is the diameter and length needed? Is the size anywhere close to an HK pivot or hand guard pin size? (I've got lots of those!)

    On the chambering problem, I'm sure you've cleaned the burrs off and polished the edges of the barrel chamfer you just added so you likely have a weak recoil spring. What is the free length, wire diameter and number of coils on the original recoil spring? Anyone know what the compression force is for a good spring?

    It goes back to my original statement regarding a gun (build or buy) where there are no spare parts on the market.

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