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Thread: 460 rowland mod for vmac 45 - blowback calculations help

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    460 rowland mod for vmac 45 - blowback calculations help

    So im looking to purchase a vmac45 and to fire 45 super loaded to 460 rowland pressures.
    my idea to increase the bolt weight is such
    add a buffer tube adapter and extra long 8.75 buffer tube
    i would use strike industries ar10 flatwire spring in it
    i would use a 1.66 pound tungsten carbide rod in the buffer tube 4 inch long 1 inch od
    i would use a 4 inch long 1/2 od tungsten carbide rod that would sit against the bolt and go through the receiver into the buffer tube. i would need to drill a hole in the receiver and in the buffer and a recess in the bolt, this would be .416 pounds.
    im adding more than 2 extra pounds to the bolt weight.
    also, the bolt travels around 2.8 inches and this rod stick in 1.1 inches into the tube so thats 7.9 inches that the 1 od weight will go into the buffer tube.

    now my question is
    what will my bolt velocity be with 230 grain going at 1350 fps?
    what will it be at 230 at 870 fps?
    what is the bolt velocity with the standard bolt weight?
    also for anyone with an ar15 buffer and stock on there mac 10s, do i have the room and ability to drill that 1/2 inch hole for my rod? and i would like to drill a recess in the bolt just so it stays in place.

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    Registered User Deerhurst's Avatar
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    I have a TASK style setup on my M10/45. It uses a 1/4" op rod to an AR buffer. 1/2" sounds pretty excessive.

    I wouldn't just drill. A mill can go a long way.

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    Quote Originally Posted by Deerhurst View Post
    I have a TASK style setup on my M10/45. It uses a 1/4" op rod to an AR buffer. 1/2" sounds pretty excessive.

    I wouldn't just drill. A mill can go a long way.
    by task do you mean like what i describe? and yes 1/4 would be easier but im trying to add as much weight as i can.

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    Registered User Deerhurst's Avatar
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    A TASK conversion uses an op rod from the bolt to an AR buffer in an AR buffer tube. Removes the spring from the guide rod and uses the buffer spring instead.


    When I added wright to my TASK setup my ROF just went up. You also have to add spring.

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    The guy to talk with would be Jim Weaver. 336-254-8758. taskslowfire@cncgunsparts.com as he is one of the co inventors of the TASK slow fire conversion. He did my M10 TASK conversion. The M10 is a tougher conversion as there is a much shorter throw behind the sear point of the M10 than the M11/NINE.

    Scott

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    Masterpiece Arms did it with a standard bolt.

    https://www.tactical-life.com/firear...a-460-rowland/
    Richard Lage
    Lage Manufacturing, L.L.C.
    www.max-11.com

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    Quote Originally Posted by Deerhurst View Post
    A TASK conversion uses an op rod from the bolt to an AR buffer in an AR buffer tube. Removes the spring from the guide rod and uses the buffer spring instead.


    When I added wright to my TASK setup my ROF just went up. You also have to add spring.
    i wouldnt remove the spring in the bolt.
    id just have the rod go through the buffer and the receiver, it would be touching the bolt and be in a machined recess. the op rod would act against a tungsten weight in the buffer tube/an ar spring.

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    Quote Originally Posted by m11stuff@hotmail.com View Post
    Masterpiece Arms did it with a standard bolt.

    https://www.tactical-life.com/firear...a-460-rowland/
    I wouldnt trust that unless the bolt was made up of almost entirely tungsten, also they dont have anymore bolts left for that and i cant find any for sale.

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    btw i know this will work i just want to know specifically what my rpm will be with 460 rowland and 45 acp
    also, would be good to know if theres enough room to use a 1/2 op rod as i currently dont have a vmac 45, im waiting for more to come into stock.

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    total bolt weight is now 76 oz

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    so what's it use for mags?

    Standard GG mags?

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    Quote Originally Posted by root View Post
    so what's it use for mags?

    Standard GG mags?
    Yes, also the total bolt weigh is gonna be 82.15 ounces. I'm also adding in a ar10 strike industries flatwire spring to the buffer tube. The op rod is gonna be jb welded to the bolt and to the tungsten weight. Im not sure whether or not i will need to cut down on the spring since it may not leave enough room for the bolt to fully cycle.

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    Conservation of momentum is the principle you need to pay attention to. Momentum is velocity times mass. (Not energy, which is 1/2 * mass * velocity ^2 )

    The momentum of the bolt will match the momentum of the bullet and exhaust gas.

    Bolt velocity * bolt mass ~= bullet velocity * (powder mass + bullet mass)

    Bolt velocity ~= (bullet velocity * (powder mass + bullet mass))/ bolt mass

    Once you know bolt velocity and weight, you can calculate bolt energy and use that to calculate the propper spring coefficient for the recoil spring.

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    I believe that you can find most, if not all, the answers to your questions by following the guidance provided in AMC Pamphlet 706-260 (February, 1970), Engineering Design Handbook, Gun Series, Automatic Weapons - available as a free 10.9 MB download.

    MHO, YMMV, etc. Be well.

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    Quote Originally Posted by Fishman View Post
    Conservation of momentum is the principle you need to pay attention to. Momentum is velocity times mass. (Not energy, which is 1/2 * mass * velocity ^2 )

    The momentum of the bolt will match the momentum of the bullet and exhaust gas.

    Bolt velocity * bolt mass ~= bullet velocity * (powder mass + bullet mass)

    Bolt velocity ~= (bullet velocity * (powder mass + bullet mass))/ bolt mass

    Once you know bolt velocity and weight, you can calculate bolt energy and use that to calculate the propper spring coefficient for the recoil spring.
    ive tried firing it and with a clipped flatwire spring its enough the case to partially eject.
    how would i go about calculating my needed spring coefficient?
    Last edited by Hannibalbarca; 11-25-2020 at 07:28 PM.

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    If you know bolt velocity and weight, you can calculate bolt energy.

    This needs to be equivalent to the potential energy of compressing the spring the distance that the bolt travels.

    Bolt energy = (bolt stroke length * (spring force fully compressed with bolt fully rearward + spring force partially compressed with the bolt fully forward)/2)

    The spring force compressed in each position will depend on the length of the spring, the spring coefficient (which changes when you clip coils) and the compression distance in each position.

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    Quote Originally Posted by Fishman View Post
    If you know bolt velocity and weight, you can calculate bolt energy.

    This needs to be equivalent to the potential energy of compressing the spring the distance that the bolt travels.

    Bolt energy = (bolt stroke length * (spring force fully compressed with bolt fully rearward + spring force partially compressed with the bolt fully forward)/2)

    The spring force compressed in each position will depend on the length of the spring, the spring coefficient (which changes when you clip coils) and the compression distance in each position.
    i guess ill need to get the spring specifications from the manufacturer. its strike industries flatwire spring. i know there are calculators for spring force online but i couldnt find one for flatwire springs

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    Just measure how much force it takes to compress it 1 inch

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