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Thread: Cetme Locking Pieces for Suppression?

  1. #31
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    That is a very interesting article and he does have a point about the complications involved. Some I hadn't even thought of like the time available to grab data. Nice to see he listed all the material and tech specs. The big problem comes in when you have to write your own software. I can type on this computer but no way I can program it.....

    Rather than going with the set up he has high speed video might tell you more. Bolt velocity will be affected by the locking pieces and if you can measure that you can get the info you need, maybe?

    Frank

  2. #32
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    Yeah they over complicated it. if you can do basic algebra or trig no special computer software needed, just run everything to the O Scope and set your triggering value accordingly. the scope will pick up the shot from the accelerometer and give you a voltage over time the sensor manufacturers specs will call out what voltage means what in g force, and you write a spread sheet with your data point in it, you apply you r formula to go from voltage to G force and have Exel spit out a graph. done deal. All that crap they have laying around is not needed. well it's needed for how they did it. There was a college science team that did this same test a few years ago. But still yes money, Oscilloscope = $500-$900, accelerometers = $50-$200, + time and ammo. It adds up quick. See you need a scope that has a high frequency 100mHz is about right, then you need one with a rise time in the nanoseconds so when the shot goes off you don't loose half your data waiting for the scope to trigger

  3. #33
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    Holescreek was nice enough to send a 35* locking piece my way to test in my C308. For the specifics, this is the same C308 I had to send back to Century a few times to make right. Finally they replaced the carrier group with a later CETME C carrier that appeared to be only lightly used. With the new part the bolt gap measured at .016. With Holescreek 35* locking piece I measured the gap at .008.

    The rifle is running a YHM brake, and a Form 1 titanium can with baffles from Rusty's Services. I recently had him swap the endcaps to work with the YHM QD mount, and a nicer front cap. Here is a pic of the baffle design and the old end cap before sending it in for the upgrade.


    New brake and end cap design, and the monstrosity this is with the can hanging off the end.



    I didn't have a ton of time, but was able to run my 42.5gr H4895 under a 155 HPBT, and some ZQI through it. With the can in place the handload ran great, and was very soft shooting. The ZQI also ran with no issue, but I did notice an increase in felt recoil. Then I decided to test my luck without the can. I didn't run the handload, but the ZQI all cycled fine. Recoil was a soft push. I did have a double, which could be chalked up feathering the trigger to get good groups off the bench.

    When time allows I will get setup out back again and I would like to test more rounds, and different loads unsuppressed.

    Here are pics of the cases.
    Handload suppressed


    ZQI suppressed


    and the ZQI unsuppressed

    the cases look almost usable.

    It's interesting that this rifle runs unsuppressed when Holescreek's rifle wouldn't. I am wondering if perhaps my recoil spring is worn or weak.

  4. #34
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    Even if the recoil spring is weak and the rifle runs ZQ1 without discomfort I'd just go with it.

    The odd part of the puzzle is that same 35LP added one or two thousandths to my bolt gaps (two different rifles) but was .008" short in your rifle (Still in spec though). I need to think about that one for awhile.

    Just out of curiosity, we're you able to hear the recoil spring noise transfer through the stock? I still remember the first time I noticed it, kind of sounds similar to the spring noise in an AR15 butt stock.

    The fired cases look like you'd benefit from a plastic port buffer (for reloading).
    Last edited by holescreek; 09-12-2018 at 06:12 PM.

  5. #35
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    Quote Originally Posted by holescreek View Post
    The fired cases look like you'd benefit from a plastic port buffer (for reloading).
    I was just going to say the same thing, a port buffer is definitely needed.
    14EH AIT Instructor-PATRIOT Fire Control Enhanced Operator/Maintainer

  6. #36
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    Quote Originally Posted by holescreek View Post
    Even if the recoil spring is weak and the rifle runs ZQ1 without discomfort I'd just go with it.

    The odd part of the puzzle is that same 35LP added one or two thousandths to my bolt gaps (two different rifles) but was .008" short in your rifle (Still in spec though). I need to think about that one for awhile.

    Just out of curiosity, we're you able to hear the recoil spring noise transfer through the stock? I still remember the first time I noticed it, kind of sounds similar to the spring noise in an AR15 butt stock.

    The fired cases look like you'd benefit from a plastic port buffer (for reloading).
    I don't recall hearing anything like that, but will look for it the next time I get out back. I will also recheck the bolt gap with this piece and the original.

    Quote Originally Posted by scottz63 View Post
    I was just going to say the same thing, a port buffer is definitely needed.
    I will add that to my "to do" list. This rifle really does a number on brass.

    Edit:
    So I think there was some end user error in that bolt gap measurement. I was just down stairs and was getting inconsistent measurements. One time it was .008, and the next it was about double that. I swapped my locking piece, slap the handle, dropped the hammer and it measured .016 5 times in a row. I did notice that with the original locking piece it is much easier to charge the rifle. Then I checked the cocking piece gap to make sure my carrier wasn't riding on it. No issue there either.

    I swapped the 35* piece back in and it measured it again 5 different times, slap the handle, drop the hammer, and measure. Now I am seeing .017/.018. This is when I realized the dummy with the tool screwed up. It appears that the .009 was sticking to the back of the .008. I am going to bring my feeler's with me the next time I am out back just to ensure that is what is going on, and will check it at the end of every mag just for kicks.
    Last edited by zer0daze; 09-13-2018 at 06:34 AM.

  7. #37
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    Sounds like the gap question might be resolved then. One of the reasons I hesitate making LPs for others is the uncertainty of the condition of their rifles. As you can see, zer0daze rifle will run unsuppressed with a 35 where mine wouldn't, regardless of barrel length. It's a plus for him but it could've gone the other way too. I had another instance years ago where a customer said his gap grew .018" to a .036". It took many emails to get him to look into his bolt head where he discovered a piece of brass lodged.
    It's very hard to get LP length spot on because the ratios of the trunnion angles, wear of the bolt head and rollers vary so much.

  8. #38
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    I loaded up a couple of mags with a box of my handloads and a box of ZQI. Both full mags functioned with no issue without the suppressor. With the can I ran a handful more of each flavor and did not hear the carrier hitting the buffer. There was no AR sproing.

  9. #39
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    Good to hear!

    As I get more rounds through the pipe on the bullpup I'll keep trying different LPS to see if it'll function with smaller ones. Same with my other Cetmes. My test gun hasn't been shot a lot, maybe a couple hundred rounds.

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