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Barrel fluting post build affect accuracy?

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  #15  
Unread 05-02-2005, 08:52 AM
ds ds is offline
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Re: Barrel fluting post build affect accuracy?

One error and one omission in my last post.

Error, the sensor looks to be on the ouside of the barrel not inside.

Omission, calibre I think is .308 Win (AR 10 rifle).

David.
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  #16  
Unread 05-02-2005, 10:27 AM
LB LB is offline
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Re: Barrel fluting post build affect accuracy?

[ QUOTE ]
20 shots up to 152 deg 5 minutes cool down to 130 ambient temp at 82


[/ QUOTE ]

What would be interesting is data on accuracy, for the second half, but 152 is beyond warm, since you cannot grasp the barrel at that temperature without burning your hand. And, that is with a cupcake chambering. Anyone that continues to shoot a hot barrel will eventually be rewarded with an erroded throat and degraded accuracy. I always put my hand on my barrel to judge whether or not I can continue. I hope it is a common practice, especially on warm days? In any case, stainless barrels are the only kind I buy.

What I see from the previous post is that the change in barrel ID is negligible, if at all, and the ID increases, if it does. It does not address fluting a previously manufactured barrel, or the question of uneven expansion in the area of the flutes. Since it does not, I will continue to assume that it is (at best) negligible, and probably not a valid concern.

Good hunting. LB
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  #17  
Unread 05-02-2005, 11:45 AM
ds ds is offline
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Re: Barrel fluting post build affect accuracy?

This I guess is going beyond my means, but an idea would be to have three digi meters with three sensors, one probe type to monitor internal barrel temperature and two external one on the ribs of the flutes and one in the flutes, and monitor temperatures over time over number of rounds fired.

It would show if the fluted areas got hotter than the non fluted areas and if the fluted areas cooled down quicker. Interperating the results is where I am out of my depth.

David.
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  #18  
Unread 05-02-2005, 02:36 PM
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Re: Barrel fluting post build affect accuracy?

The linear expansion of the barrel would be negligible for most purposes.The Thermal Coefficient of Expansion for 416R works out to about 0.00002 per degree starting at 68F/20C (thats the std. reference temp for ISO and ANSI) so a 20 degree increase(88F) would cause the length and dia of the barrel to grow by 0.0004. As to stiffness Varmint AL has a study on that, www.varmintal.com/aflut.htm that looks interesting.
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  #19  
Unread 05-02-2005, 02:50 PM
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Re: Barrel fluting post build affect accuracy?

So, from 68* up to 118*, a 50* increase = .001 larger bore diameter?
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  #20  
Unread 05-02-2005, 02:58 PM
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Re: Barrel fluting post build affect accuracy?

DS,

Infra red laser thermometer, they're pretty cheap these days and you can check the temp at any location, even up in the throat if you're a good aim.
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  #21  
Unread 05-02-2005, 03:07 PM
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Re: Barrel fluting post build affect accuracy?

The thermal expansion coefficient for steel in the temp range of 20C-100C is from (1x10^-5)/C to (2x10^-5)/C. Longtooths post says 2x10^-5/C for 416 steel.
This is a fractional change. So if you went from 20-100C the fractional change is 0.0016.
This means that a 30" barrel lengthens by 0.048 inches. If the barrel is 1" thick, it will become 0.0016 inches thicker.
A .2640 bore will open up by 0.0004 inches (less than 1 thou).
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