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Thread: Can a Open Bolt Parts Kit Work in a M16 without Modification?

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    Can a Open Bolt Parts Kit Work in a M16 without Modification?

    Hello all:
    There was a open Bolt M16 that Colt made years ago and it had a slower rate of fire and the Guns were Full Auto and Safe only, no semi setting
    There is a kit for sale as pictured below and I wonder if you can drop in the parts without drilling anything into a M16
    I wonder if the M16 sear is different than this one?
    Also does anyone know what the part in the lower left corner is?
    Thanks for looking
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    It's a drop-in w/o modification to an M-16 spec lower.......the part in the lower (L) is the connector / connector link. The auto sear is completely different....as are the rest of the components

    Last edited by Villafuego; 01-20-2021 at 02:51 AM.

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    It seems to me, a big part of the reduction of the ROF is that as part of the open bolt package Colt used a hydraulic buffer for a rifle stock. There has been several threads from the member "amphibian" as to using a Tubbs flat wire spring and Kynshot hydraulic buffer.

    Tactical Innovations sells a open bolt fire control kit for use with their American 180 based upper. Their .22 kit fire control just releases the bolt. The auto sear is missing the part that releases the hammer. There is a picture https://www.tacticalinc.com/catalog/product/00531 of the open bolt .22lr kit. It is my understanding that the open bolt firing system is harder on the hammer pin. The hammer stops the bolt group such that the hammer has a shearing effect on the hammer pin. I would think that is why Tactical Innovations doesn't sell that part or a modified carrier as they would be liable for receiver damage. Open bolt fire control is a cool concept for the M16, but damage to a $20,000.00 M16 RR is why the open bolt system didn't become popular.

    Scott

    ETA at over $1,100.00 with shipping it does seem to have all the parts required for open bolt function. I would want a set a set of stainless steel fire control pins.
    Last edited by A&S Conversions; 01-20-2021 at 06:29 AM.

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    Quote Originally Posted by A&S Conversions View Post
    Open bolt fire control is a cool concept for the M16, but damage to a $20,000.00 M16 RR is why the open bolt system didn't become popular.

    Scott
    +1....I would never use the Colt open bolt fire control in a transferable lower.
    In this video, he talks about it being around 650-700 RPM https://www.youtube.com/watch?v=ZYO3soKONHg
    This document mentions 600-750 RPM. http://www.sadefensejournal.com/wp/the-colt-lmg/2/

    Don't think I've seen someone actually clock an open bolt LMG with a timer.

    I have clocked my friend's LMG in closed bolt though.




    You can see here that just by using my recommended buffer tube/buffer and spring recommendation, I'm getting what you expect from an open bolt LMG w/ a hydraulic buffer....all without worrying about damaging a transferable lower.
    Also note that I'm not resorting to a fixed rifle stock w/ rifle buffer tube like you would see on a factory LMG complete setup. Pretty sure if I used the Kynshot rifle buffer, it would drop it slightly more due to additional mass but I doubt it would be more than 30-40 RPM slower.


    Now this is my 16" Rifle gas upper running at 564 RPM w/ A5 buffer tube, hydraulic Kynshot RB5007 and 556 Tubb flat spring.


    Same upper with Surefire OBC, A5 buffer tube, Kynshot RB5005, spacer and 556 Tubb spring - 535 RPM.


    Same as above and even running on a 10.3" MK18, I'm getting in the low 600's. 625 RPM.


    So as Scott mentioned the hydraulic buffer is one of the main components that slows down the cyclic rate. The flat springs make a huge difference as well. I suggest you read this article I have on my website:
    http://www.c3junkie.com/?page_id=977
    Last edited by amphibian; 01-20-2021 at 09:43 AM.

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    Villafuego,Scott and Amphibian...Thanks so much for sharing your knowledge with me. Thats great!!
    Any One Who Thinks The Pen is Mightier Than The Sword
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    You should also see this video interview with Jim Sullivan (one of the engineers that worked with Stoner to downsize the AR10 to the AR15) https://www.youtube.com/watch?v=gOUKXIrDE0I&t=740s

    He is the inventor of the Ultimax and several other guns.

    He is the inventor of the Surefire OBC.

    The Surefire OBC and the LMT Enhanced carrier are the only two that I know of that are using a modified cam pin path.
    The LMT has an additional gas port hole which I'm not sure but I'm guessing may cause it to not work properly in rifle gas length configurations.....while you can see in my posts, I have no issues with any length gas system with the Surefire OBC.

    Then the Surefire OBC also has the spring loaded carrier weight and the extended stroke length with the shortened carrier key that you really don't have to take advantage of you don't want to...

    Then consider that the Surefire is around half the price of an LMT, I think it is a no brainer to get the Surefire if you are into this sort of thing.

    I also don't see any downside to going with the Tubb flat springs.

    Lastly is the hydraulic buffer which I think is worth it but I do certainly understand some people's hesitation to using them in case of failure.

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    Amphibian, how do you like the RB5005 setup with the surefire bcg? Worth it? Maybe not / too slow, and/or “chuggy”?

    Also, which spacer did you use? I’m just curious because I was thinking about a similar setup, but based on my measurements, if you didn’t have a spacer, the bcg would definitely bottom out with a A5 tube + RB5000 (what I bought for the setup).

    Unrelated, I need to get your new email address now that the old one doesn’t work. I’m the guy who worked with you on the ejector spring issues with banshees last year. I hope all has been going well, by the way.

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    Quote Originally Posted by lllest View Post
    Amphibian, how do you like the RB5005 setup with the surefire bcg? Worth it? Maybe not / too slow, and/or “chuggy”?
    I like it. It isn't too slow or chuggy/bouncy.

    Also, which spacer did you use? I’m just curious because I was thinking about a similar setup, but based on my measurements, if you didn’t have a spacer, the bcg would definitely bottom out with a A5 tube + RB5000 (what I bought for the setup).
    I'm using a custom spacer made from Delrin but I think it is equivalent to 2 or 3 quarters.

    Also you mentioned the RB5000 which I personally don't like. I'd rather use the RB5005 for when I need a carbine length equivalent hydraulic.

    The downside is other than price is whenever you want to switch to a different upper that uses a proprietary carrier like a Shrike, belt fed FM9 9mm then you need to remember to change out your buffer / spacer.

    Unrelated, I need to get your new email address now that the old one doesn’t work. I’m the guy who worked with you on the ejector spring issues with banshees last year. I hope all has been going well, by the way.
    Hit me up on IM regarding email.

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