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3750 fps 257 weatherby

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  #1  
Unread 07-22-2013, 07:29 PM
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3750 fps 257 weatherby

Just got to shoot my Hart .257 weatherby mag. Chrono at 25 yards average speed was 3750 fps. Factory115 nosler bt. Very impressed with the speed grouping at 1.23 inches. Gonna do load development this week. Hopefully I can tighten up those groups and still keep it around 3400 fps.
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  •   #2  
    Unread 07-22-2013, 08:23 PM
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    Re: 3750 fps 257 weatherby

    Holy crap!!! That's some serious speed! My .257 Wby load with the Berger 115 VLD's is right around 3,300 MV and grouping very nicely. I'm using 70.0gr of H1000 for it, seated 0.005" shorter than magazine length.

    Might I pry for your load data and COL?
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      #3  
    Unread 07-22-2013, 09:03 PM
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    Re: 3750 fps 257 weatherby

    Man, you got a fast one. I built a custom 28" barrel 257-300 wby. Necked down a 300 wby case to 257, and with 110's was about the same as your 257.

    Jeff
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      #4  
    Unread 07-22-2013, 09:23 PM
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    Re: 3750 fps 257 weatherby

    I would double check this with another chronograph on a sunny day. Two years ago I was with some folks from Weatherby to over pressure the Accumark action. Weatherbys are engineered not to destruct through overpressures. They will route the destructive gasses to go through the floorplate or out the bottom of the stock and away from the shooters face/head. We were using the 257 to do this demonstration. I can tell you that we never reached this velocity before the primer completly destructed and cartridge was done. This design on the action is why Weatherby contracted to Norma to make its brass. The brass is softer than other makes to let the primer go before the pressures spike so high that the engineering to reroute of the the gasses would not work. This post reminds me of a man that guarenteed me that he had a 300 win mag that would do over 3500 fps with 190 Hornadys. He even used my chronograph at the range to verify that his Winchester would out do the Weatherbys I build. He indeed did have muzzle velocitys in the high 3400 range. But when I pulled and weighed the bullets they were only 150 gr! Have you double checked the weight of the bullet? Happy and safe shootin!
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      #5  
    Unread 07-22-2013, 09:32 PM
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    Re: 3750 fps 257 weatherby

    Something is amiss. That is super fast for a 115 grn projectile. Pressure must be extreme. If no pressure signs check your chrono. Light angle, levelness and even external temp can make a difference. Also weatherby factory ammo tends to be very temp sensitive. I had a 30-338 I was shooting factory ammo sighting for a buddy and it blew primers and locked the bolt. It was fresh off the shelf. Contacted weatherby and they replaced the ammo.
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      #6  
    Unread 07-23-2013, 06:04 AM
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    Re: 3750 fps 257 weatherby

    got to agree. I doubt mine would even get to 3400 without leaving primers in the action. You have to be running some real extreem pressures or have a real optimistic chronograph. First thing id try is moving your chrono out about another 10ft. You could be reading the muzzle blast.
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      #7  
    Unread 07-23-2013, 09:07 AM
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    Re: 3750 fps 257 weatherby

    most guys I know of were (or are) getting around 3350fps with a 26" barrel and 115 /117 grain bullets. These rounds were pretty hot!
    gary
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