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Thread: Hornady says no non monolithic supersonic bullets in MCX 1:5 twist .300blk with can

  1. #11
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    So, here's a new wrinkle:

    Someone on another forum just shared with me a formula for calculating bullet RPM. 12 / twist rate * velocity *60

    Based on what little chrono data I've been able to find on 110gr .300blk, it looks like 1950fps muzzle velocity would be very optimistic on a 6.75" bbl, with something in the 1900-1850 range more likely. According to the formula shared with me (12/5*1950*60), that works out to 280,800 RPM, worst case. The Hornady guy was only worried about RPM above 300,000.

    Was the Hornady guy calculating based on muzzle velocity for a 16" barrel? It looks like it. I've seen 2300 FPS listed as the MV for 110gr V-max. 12/5x2300x60=331,200 That's almost exactly the figure the guy quoted.

    It's looking more and more like the two incidents I've found documented on the internet were caused by first, a specific 125gr all-copper "slotted" HP bullet and second, a frangible bullet (which I've always read should not be used with a suppressor, in any caliber).

  2. #12
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    Here is a link to the Hornady 110gr Vmax 300 black out ammo. 2375 FPS out of a 16" inch barrel. https://www.hornady.com/ammunition/r...gr-v-max-black
    What kind of RPM would I be getting out of my 9 inch 1:5 twist blackout barrel ?
    Last edited by Biggy; 03-14-18 at 02:14.
    "A free people ought not only to be armed and disciplined, but they should have sufficient arms and ammunition to maintain a status of independence from any who might attempt to abuse them, which would include their own government."
    - George Washington

  3. #13
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    Quote Originally Posted by Biggy View Post
    Here is a link to the Hornady 110gr Vmax 300 black out ammo. 2375 FPS out of a 16" inch barrel. https://www.hornady.com/ammunition/r...gr-v-max-black
    What kind of RPM would I be getting out of my 9 inch 1:5 twist blackout barrel ?
    110gr Vmax from a 9" bbl is around 2190 FPS.

    12 / 5 * 2190 * 60 = 315,360 RPM

    2100 FPS gets you down to 302,400.

  4. #14
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    Quote Originally Posted by Bret View Post
    Is such a fast twist really required to stabilize the bullets? I've never heard of a twist that fast.
    No......at least with the Rattler the twist rate is a factor of the barrel length. You need at least one full rotation of the bullet before it leaves the barrel to achieve stability. Hence the 5 twist in a 5.5 inch barrel.

    The RPM of the bullet is not just a factor of the twist rate, velocity is the second part of the equation. The faster the bullet travels down the barrel, the faster the rpm.

    With the Rattlers shorter barrel I'd be surprised if it could reach the RPMs required to spin apart most conventional bullets. Maybe some weird pre fragmented designs might have problems.

    It's a pretty simple test. Take your suppressor off and shoot a couple of mags of your ammo at a big piece of white poster board.

    You'll know if your bullets are slinging apart.

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