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Changing cyclic rate

Discussion in 'NFA Firearms and Accessories' started by o Unforgiven o, Aug 30, 2010.

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  1. o Unforgiven o

    o Unforgiven o Member

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    How do you go about changing the speed of a machine gun? I know that when building them the designers can to an extent change the rate of fire. How?
     
    Last edited by a moderator: Aug 30, 2010
  2. zoom6zoom

    zoom6zoom Member

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    The speed you refer to is called the cyclic rate. How it can be changed varies depending on the design of the gun. Many things can affect it, including weight of the reciprocating parts, spring strengths, size of gas ports to name a few... you really have to understand how the particular weapon system works first.
     
  3. Sam1911

    Sam1911 Moderator

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    Evan, I've taken the liberty of moving your "slightly off topic" post in the belt-fed-thread to a separate thread of it's own, as I believe it is an interesting question and one deserving of some good answers.

    I can think of several answers right off. One is that shortening the bolt travel raises the cyclic rate, in general. If you play with submachine guns much, you can get "buffers" that insert behind the bolt and reduce how far back it can travel. Of course this can negatively affect reliability -- but to a point, with many guns, you can get away with a noticeable reduction in bolt travel distance. The bolt doesn't go back quite so far, thus it doesn't take so long to go back and come forward, thus it all gets done quicker and the cyclic rate rises.

    More traditional ways of regulating the cyclic rate would be lockwork adjustments that hold back firing of the next shot until "something" happens. The AKM has a device that acts as an out-of-battery fire prevention safety but it is more commonly thought of as a cyclic rate reducer or hammer retarder.

    There are probably just as many different solutions to the question as there are gun designs. Hopefully some more knowledgeable members will chime in to explain some of them.
     
  4. Sam1911

    Sam1911 Moderator

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    Here's a link to a thread on UZITalk.com regarding the effects of buffers in an Uzi (what else? ;)) with video of the results. http://www.uzitalk.com/forums/showthread.php?t=52517

    Note, there's enough room in the receiver of an Uzi to reduce the bolt travel distance by 3/4", 1", and even 1-1/4"!
     
  5. jmorris

    jmorris Member

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    Weight is the easiest. Here are the differences in bolt weight between a PS M10/9 bolt and a Cobray M10?9 bolt.

    DSC01917.jpg
    DSC01921.jpg
    DSC01922.jpg
    DSC01923.jpg
     
  6. KingTiger

    KingTiger Member

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    Those are some good examples jmorris. For my SWD M11/9, I have 4 different 9mm bolt weights that vary the cyclic rate between 1200 - 550 rounds per minute, and also a .22 LR bolt that runs between 800-900 RPM.

    A suppressor tends to increase the cyclic rate due to back pressure.
     
  7. taliv

    taliv Moderator

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    for m16 pattern, you can use a pneumatic buffer
     
  8. Carl N. Brown

    Carl N. Brown Member

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    For the Thompson M1928, the actuator (the part of the bolt with the bolt handle) was made heavier than that of the M1921.
     
  9. SDC

    SDC Member

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    As you can see above, it really depends on the particular design; you can use lighter or heavier bolts, heavier or lighter springs, smaller or larger gas ports, thicker or thinner (or more or less resistant) buffers, and on and on. Did you have a particular design in mind?
     
  10. Blakenzy

    Blakenzy Member

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  11. rcmodel

    rcmodel Member in memoriam

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    The early M16 had the cyclic rate changed (too fast) by accident when they changed from stick to ball powder. They changed it back with different powder again.
    But it was still too fast, so the buffer weight was increased.

    rc
     
  12. gun guy

    gun guy Member

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    First, unless you are engaged in some mission specific operation, why on earth would you want to change the rate of fire. Already the rate of fire of the mac/cobray style weapons is an insane speed of 1,200+rpm. At this rate, hit probabilty is near 0, while ammo expanduture is horrific. In a nutshell, by the time you get your finger off the trigger, the gun will be empty, you will have missed your target, and have to call a time out in a gunfight to reload. 500 rpm is near perfect for a smg, if you wish to actually acomplish something other, than a fireworks display.
     
  13. jmorris

    jmorris Member

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    Most of the time you want to change the rate of fire to make it slower. Why is hit probability near 0? Even with the light PS bolt you can "single" an M10 on auto. They certainly don't go jumping all over the place. Click on this photo.

    th_VID00032.jpg

    He doesn't single but 3 round bursts the first two pulls.
     
  14. PTK

    PTK Member

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    So, gun guy... you have precisely zero experience with any Military Armament Co. made firearms, and you've gleaned that from what other people have said here and there?
     
  15. MrCleanOK

    MrCleanOK Member

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    M240 machinegun rate of fire is varied with a 3-position gas regulator between the gas port and the gas tube.
     
  16. TexasRifleman

    TexasRifleman Moderator Emeritus

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    I guess that's been shown so many times on TV and in movies, and repeated so often on gun forums, that it's become Gospel.

    It's simply not true of course. Like any firearm the Mac's require skill and proper technique to be used effectively. In the hands of someone with experience shooting them I would not want to be on the receiving end. They can be quite devastating things.
     
  17. gun guy

    gun guy Member

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    Actually, I have probably fired more automatic weapons, (I could go into everything from 3 in naval guns, the 40 mm with and without amplidyne power drive,on down to small arms made in the usa/europe/and comblock countries etc, but it would take quite awhile) than you have seen ptk, and in combat situations. You will notice the weapon in the picture has the added weight of a suppressor/extension, this does hold down muzzle flip, but you are adding more weight to an already morbidly obese handgun. At this point, a thompson with the stock removed is about the same size, and a far better weapon. I have found the best hit probability is with slower cyclic rates such as the uzi, or the h&k mp5 series. IMO the mac/cobray weapons look great on filim. In a tactical situation, the best use of those high cylic rate weapons, is to tie a string on them,,and toss them into the rooom. The results are about the same as trying hand fire them. But then, that was just my observation, after actually trying to use one, in combat vs standing on a range on a sunny day. We used to have a saying, never assume your safe from a machinegun, just because you are standing in front of one. As far back as ww1 Alvin York proved this by using aimed fire, to knock out machine gun nests that were hammering rounds at him. In a tactical setting, one man, with a mac can pour fire while the rest of the team takes targets of oppertunity. In a solo setting, only a fool, would attempt to engage a skilled opponent, with a full auto weapon, he would be out of ammo about the time things got truly interesting.
     
    Last edited: Sep 1, 2010
  18. jmorris

    jmorris Member

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    It’s a machine gun not a pistol even if it were semi auto it would be an SBR under NFA. In any case the obese MAC weighs less than either the Uzi or almost all of the variations of the MP5 (some of them even weigh more than the Uzi). I will agree with your last comment, heavier and/or slower rates of fire can help with accuracy, but then again we are talking about MG’s.

    The MP5 SD is a very controllable SMG at almost 8 lbs but I have bolt action rifles that weigh less (including optics), talk about slower rate of fire and a noticeable increase in accuracy…
     
  19. PTK

    PTK Member

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    Frankly, gun guy, I don't believe you.

    For what it's worth, here's his original message, sent via PM:

    Everyone please note that this "expert" just said that "Corbay" (would that be Cobray?) MAC styled SMGs have hammer failures. Open-bolt guns do not have hammers. ;)

    Furthermore, what year are you alleging that you were running a covert op from a freaking missile submarine?

    Or are you just that super-secret, that you had this firearm with a team of men prior to it being developed?

    For what it's worth, most SMG matches I've been to recently have been won or at the very least had extraordinary competitors (placing in the top 5, which is usually extremely close) using just the family of guns you're trashing. Or are they not skilled, or under stress? ;)


    EDIT: Additional information, apparently he's quite the expert.

    My bad, I suppose that the mistakes about simple operation of firearms you're familiar with is due to vast experience.






    EDIT 2: I would like to publicly acknowledge my mistake - the Grayback was used, post-1967, as a SEAL "Swimmer Delivery Vehicle". No offense intended or slight meant on that account. :)
     
    Last edited: Sep 1, 2010
  20. Sam1911

    Sam1911 Moderator

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    This just doesn't make sense, and is DEMONSTRABLY untrue.

    In fact, the video posted up in post 13 shows it being done.

    That technique is pretty simple. I've taught it in two minutes to middle-aged houswives who'd never fired a sub-gun before.

    Of course, that's the sort of thing you'd do on a range, but not in the jungle ... supposedly. :scrutiny:
     
  21. PTK

    PTK Member

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    I'm still at a loss as to why you wouldn't use controlled bursts in combat...
     
  22. jmorris

    jmorris Member

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    I have absolutely zero combat experience but controlled bursts are a better method for popping balloons floating across the pond than just hosing.
     
    Last edited: Sep 1, 2010
  23. JamisJockey

    JamisJockey member

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    You're using your "experience" as a stick, with which to beat down any opposing viewpoint on the use of an SMG. And nobody cares about your "stuff". Also, your stuff doesn't prove anything.
    By the way, are you perhaps a bodybuilder?
     
    Last edited: Sep 1, 2010
  24. KingTiger

    KingTiger Member

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    Here's a friend of mine shooting my M11/9 w/Lage Slow fire bolt. He had never shot a MG before. The first shot is a single, and there's another one further into the clip. Looks like he's doing the "impossible". :neener:

    th_Creekside6_20_08008.jpg
     
  25. JamisJockey

    JamisJockey member

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    Your video is obviously a fake, because an "Operator" said that it can't be done! Don't you see all the money he's spent on cars and motorcycles to prove you wrong? I'm sure that super long 4 round burst in the middle of the video made the weapon uncontrollable.
     
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