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4000 fps in a 7mm STW w/140 Bullet?

 
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  #50  
Old 03-11-2013, 05:47 PM
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Re: 4000 fps in a 7mm STW w/140 Bullet?

Crap, only one of the win pics posted. Oh well, it is representative; the other one was the same peak pressure... 70 KPSI.
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  #51  
Old 03-12-2013, 06:00 AM
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Re: 4000 fps in a 7mm STW w/140 Bullet?

That load of 76 grains of 7828 has a peak pressure spread of about 6,000 psi. I didn't see what the muzzle velocity spread was about the 3375 fps average. Such spreads with slow powders are very normal and usually cause greater muzzle velocity spreads than a faster powder at the same average peak pressure.
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  #52  
Old 03-12-2013, 06:47 AM
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Re: 4000 fps in a 7mm STW w/140 Bullet?

78 grains 7828 with the 140 sierra was my standard load for quite a few years until rl25 came along. I switched because rl25 gave me the same basic speed (3350 fps- vs 3375 fps for 7828) with significantly less pressure peak and a bit better uniformity. It is also just as capable accuracy wise; both handloads were 1/2 moa average.
Some of the peak pressure spread on the handloads was likely mixed trim lengths. I was using borrowed equipment at the time so I was more concerned with getting the ammo loaded than it being perfect. As long as the brass was usable and the charges/ bullet seating were correct it went home.
Part of the reason I asked my brother in law to help put a gauge on my rifle was the fact that there was NO data for rl25 at the time as it was a new introduction. I was very concerned that I was getting the charge weight to correct levels.
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  #53  
Old 03-15-2013, 08:25 PM
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Re: 4000 fps in a 7mm STW w/140 Bullet?

Update: 90 grains of powder and a 35 inch barrel. Possible?
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  #54  
Old 03-15-2013, 08:40 PM
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Re: 4000 fps in a 7mm STW w/140 Bullet?

I think the ultra-slow powders are producing more repeatable pressure curves these days. That's good for accuracy.
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  #55  
Old 03-16-2013, 05:10 PM
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Re: 4000 fps in a 7mm STW w/140 Bullet?

Quote:
Originally Posted by gilmillan1 View Post
Update: 90 grains of powder and a 35 inch barrel. Possible?
You will likely hit the point of diminishing returns around 30 inches on barrel; just guessing here though. I'd query some of the threads on the bug 338's for more info on that. They've been playing with long pipes for as while.

I'd guess 3700- 3800 fps top even pushing to 65,000 Kpsi+ peak and using slow enough powders for compressed charges.
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  #56  
Old 03-16-2013, 07:01 PM
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Re: 4000 fps in a 7mm STW w/140 Bullet?

Quote:
Originally Posted by Lefty7mmstw View Post
65,000 Kpsi+ peak?
That's 65,000,000+ psi ;)

Those extra zeros means the barrel's gotta be at least half a mile thick around the chamber.
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