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Published Muzzle Velocities..accurate or not?

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  #1  
Unread 05-31-2009, 10:23 PM
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Published Muzzle Velocities..accurate or not?

Hi,

I just ordered a Speed Dial for my Nikon Monarch X 2.5 x 10 x 44 Scope.

I'm mounting it on an X-Bolt 7MM WSM. I'll shoot Win. Supreme 160 Gr. Accubond.

My question is how reliable are the Factory MV's on winchester short mags?

This round has a published MV of 3050 fps. Since I got a 23" tube, my ballistics program put my MV at 3020 fps and that's what I used on the order form.

Just wondering if there is some "Blue Sky" in the factory published MV's. and if I screwed up by not running the stuff through a chrony?

Thanks,

Dee
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Last edited by Seven Oaks; 06-01-2009 at 03:20 PM.
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  •   #2  
    Unread 06-01-2009, 06:47 PM
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    Re: Published Muzzle Velocities..accurate or not?

    Depends on your rifle. There could be as much as 300 fps difference.
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      #3  
    Unread 06-01-2009, 07:29 PM
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    Re: Published Muzzle Velocities..accurate or not?

    In most cases using a factory rifle AND factory loads together the published data is very close, like around 50-65 FPS worst case. Bear in mind this is NOT in all cases, just most. Now if youre using a custom bore and chamber, then all bets are off. I have seen factory loads completely seize a bolt down in a custom barrel. My 308 Hart barrel shoots Federal GMM 168's ant just under 2800 FPS and are published at 2600. In factory sticks, 2600 seems to about right +/-. In every case, shooting loads over a chrony is by far the best method regardless of ammo type.
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      #4  
    Unread 06-01-2009, 09:16 PM
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    Re: Published Muzzle Velocities..accurate or not?

    Thanks for the replies fellas.

    Dee
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      #5  
    Unread 06-01-2009, 10:54 PM
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    Re: Published Muzzle Velocities..accurate or not?

    Quote:
    Originally Posted by Seven Oaks View Post
    Hi,

    I just ordered a Speed Dial for my Nikon Monarch X 2.5 x 10 x 44 Scope.

    I'm mounting it on an X-Bolt 7MM WSM. I'll shoot Win. Supreme 160 Gr. Accubond.

    My question is how reliable are the Factory MV's on winchester short mags?

    This round has a published MV of 3050 fps. Since I got a 23" tube, my ballistics program put my MV at 3020 fps and that's what I used on the order form.

    Just wondering if there is some "Blue Sky" in the factory published MV's. and if I screwed up by not running the stuff through a chrony?

    Thanks,

    Dee
    Most factory muzzle velocities are hard to match in factory rifles because they are tested in
    custom barrels. and are the highest velocity reached not an average of all shots fired.

    And most of the barrels are 26", most factory hunting rifles are 24".

    The only ammo I have ever seen that reaches or exceeds listed velocity is the factory
    Weatherby ammo in Weatherby calibres.

    If you have a slick Custom barrel they will make up about 50 ft/sec from the 50 ft/sec lost
    in a standard factory barrel, so they will be close to listed velocities.

    Always verify velocities with a good chronograph and use the average, if the highest velocity
    matches the factory that's fine but use the average for trajectory calculations.

    J E CUSTOM
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      #6  
    Unread 06-02-2009, 08:23 AM
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    Join Date: May 2009
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    Re: Published Muzzle Velocities..accurate or not?

    I have a chrony. It got dropped and is in for repair.

    Using the chrony previously for other calibres using Factory ammo, the variance I got off of 7MM Mag. stated velocites avg. about -55 fps below.

    My .308 avg. about -10 fps below published MV.

    My 7-08 avg. was right on the money of published data.

    I verified that the published MV for the 7WSM was from a 24" Bbl.

    This is a new hunting rifle. Won't be shot past 500 yds. I know there was alot of Marketing hype on the WSM's and was hoping the MV variance wouldn't be any worse than the above cartridges, as I could live with that.

    I ran some numbers using 2966 as MV, which is 60 ft. less than published after you deduct 1" for the shorter Bbl. It had me low 2.5" @ 500 yds. That's better than I can shoot. I hope the MV isn't much lower than that though.

    Thanks for the help.

    Regards,

    Dee
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    Last edited by Seven Oaks; 06-02-2009 at 08:30 AM.
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      #7  
    Unread 06-02-2009, 08:50 AM
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    Join Date: Feb 2009
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    Re: Published Muzzle Velocities..accurate or not?

    A guy really needs to be a reloader to shoot long range. Factory ammo is just that.....made in a factory (not to mention expensive). Unless a guy can buy an entire lot, with the same lot #, he is asking for trouble. The factories don't use the same powders available to the reloader. Powder lot numbers can vary, bullets can vary (heck I just compared two different bullet lot, same bullet/brand and the length was different by .026". So if you want to shoot factory fodder at long range, do yourself a favor and buy same lot #, otherwise you'll have to re-sight and re-do your ballistic table for every box you shoot.
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