MV Cal differences

gasrat

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Don’t know if this is the correct section or not, but here goes.

My rifle chronos at 3115 on Magnetto Speed V3. I’m running a 6mm Creedmoor with 105 Hybrids and 41.0 grains of RE16. I shot it today at 725, 813, 905 and 1000. Shooting at a water line painted through the middle of the Target. I had to adjust the MV to match what it doing at distance in the Kestrel. It trued to 3178 MV. I was holding 6.5 mils at 1000 yards.

My question is does that big of a jump seem right? I mean I know it’s good info in as I was able to hit center at all distances. Any information is appreciated.
 

Ledzep

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    I've heard of magneto speeds being up to 30-40 fps different from labradars depending on how they were attached to the gun.
     
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    gasrat

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    Been Thinking of selling the magnetto speed and investing in a lab radar.
     

    1moaoff

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    Truing dope is not always a trip deal. Once you get to 800 and 1000 mirage and light can play with vertical.
    At 600 yds how close was your dope
    At 800 yds how close was your dope
    If you were close there you should true bc at 1000
    All other data also starts to be more important the further out you get.
    Headwind or tailwind or crosswind
    Its also the time of year guys will be shooting in cooler weather.
    Is your zero spot on
    Is your bc data correct
     

    Ledzep

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    The other thing to consider is that MV spread among other things can account for .2-.3 mils worth of variance at 1000yd. Don't change your calculator on 1-5 shots. When I set my stuff up it's 10 shots at 100yd, 10 shots at 500-600, and 10 more at 800-1000 on clean steel/paper, and measure it all out to get real numbers I can believe in.
     
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    gasrat

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    Was on at all distances. Looked to be maybe .1 low at 400 on a barricade based on the grouping of 8 shots.

    I was running the bc on the box of the hybrids. I could put the FPS back at 3115 and adjust the bc of what I was running at 1000, which was 6.5 mils
     

    Steel head

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    Truing dope is not always a trip deal. Once you get to 800 and 1000 mirage and light can play with vertical.
    At 600 yds how close was your dope
    At 800 yds how close was your dope
    If you were close there you should true bc at 1000
    All other data also starts to be more important the further out you get.
    Headwind or tailwind or crosswind
    Its also the time of year guys will be shooting in cooler weather.
    Is your zero spot on
    Is your bc data correct
    This!
     

    gasrat

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    It was on at all distances. However, I just can’t see the speed being 3178fps. Mag V3 showed it at 3115 over 10 shots. I ran 275 G7. When I put the FPS back to 3115 and adjust the BC to get me 6.5 mils at 1000, the G7 is 293 and I can‘t see the 105 Hybrid having that either.
     

    NWnewguy

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    I know that people do it all the time with success but it seems odd to me to change the factor (muzzle velocity) that you know to be true in order to true your data.

    B.C changes for a lot of reasons, not limited to, but including: velocity, humidity, spin rate. I would think that if you could get it to line up, you would probably be better of truing your BC and that BC should be your actual BC in that barrel at that speed.
     

    seansmd

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    Don't get locked on the MV being right, you need to lie to the solver one way or another.

    The guiding information is true your MV at 600y(BC has very little effect all MV) then with BC 800-1000y.

    Ballistic curves are not perfect, neither are MV devices, it's just variables you are providing to an equation that estimates based on average rifles, average barrels, average bullets, etc.
     

    lte82

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    It was on at all distances. However, I just can’t see the speed being 3178fps. Mag V3 showed it at 3115 over 10 shots. I ran 275 G7. When I put the FPS back to 3115 and adjust the BC to get me 6.5 mils at 1000, the G7 is 293 and I can‘t see the 105 Hybrid having that either.
    I ran 105 hybrids over the Applied Ballistics Doppler (again) this weekend. Last year with a Bartlein I got a .286 G7, this year with a Hart barrel I got a .285 G7. I bet if you plugged in .285-.286, and bumped your velocity a hair you would be about right.

    Are you by chance shooting a 7 twist barrel? The faster twists tend to give the 105 hybrids an increase in BC judging from the Doppler data I’ve seen. An 8 twist will generally be in the .275 range, 7.5 would go .279-280, and 7 is typically .285-286. The 109s ran .295-.305.
     

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    sea2summit

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    Just gonna throw this out there but magnetospeed only says their units are 99.5-99.9% accurate so if we use 3178 as the actual velocity worst case they should still read ~3140-~3220. Going another .5% velocity on top of errors for correction seems slightly high to me. It would be interesting to throw that load against a few other chrono’s and see what they say.
     
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    Dthomas3523

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    I know that people do it all the time with success but it seems odd to me to change the factor (muzzle velocity) that you know to be true in order to true your data.

    B.C changes for a lot of reasons, not limited to, but including: velocity, humidity, spin rate. I would think that if you could get it to line up, you would probably be better of truing your BC and that BC should be your actual BC in that barrel at that speed.
    Your theory of not changing a known only works if the software is perfect.

    Software varies from manufacturer to manufacturer and it’s not an exact science yet (if it was, they would all use the same algorithms).

    So, yes, you might have to change a known quantity, because that’s one of the only options we have to change. We can’t mess with what’s under the rest of the hood of the calculator.
     

    1moaoff

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    Was on at all distances. Looked to be maybe .1 low at 400 on a barricade based on the grouping of 8 shots.

    I was running the bc on the box of the hybrids. I could put the FPS back at 3115 and adjust the bc of what I was running at 1000, which was 6.5 mils
    Don't true based on positional shooting
     

    Dthomas3523

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    For example, I have absolutely zero idea what my actual MV is for my vudoo with this lot of sk ammo. I used the box velocity and the BC provided by AB.

    I then used the dsf (since subsonic) to true the software to the real world dope. It’s been spot on at matches out to 350 yds for almost 5,000 rounds.

    I don’t give two shits what the inputs are as long as it spits out the right solution.

    If you find over time it’s not accurate all the time, start digging into the weeds. If not, who cares.
     

    1moaoff

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    And don't forget all the other variables... is your zero 100% at 100yds 100% scope height, clicks, atmosphere,,, each on its own is miniscule... but errors add up!
     

    gasrat

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    I ran 105 hybrids over the Applied Ballistics Doppler (again) this weekend. Last year with a Bartlein I got a .286 G7, this year with a Hart barrel I got a .285 G7. I bet if you plugged in .285-.286, and bumped your velocity a hair you would be about right.

    Are you by chance shooting a 7 twist barrel? The faster twists tend to give the 105 hybrids an increase in BC judging from the Doppler data I’ve seen. An 8 twist will generally be in the .275 range, 7.5 would go .279-280, and 7 is typically .285-286. The 109s ran .295-.305.
    Yes, I am running a 7 twist barrel.
     
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    gasrat

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    Just gonna throw this out there but magnetospeed only says their units are 99.5-99.9% accurate so if we use 3178 as the actual velocity worst case they should still read ~3140-~3220. Going another .5% velocity on top of errors for correction seems slightly high to me. It would be interesting to throw that load against a few other chrono’s and see what they say.
    I’m gonna check it with my friends Lab Radar when time allows.
     

    gasrat

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