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Old March 12, 2010, 04:48 PM   #1
riverwalker76
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What Bullets ..... 1:12" Twist Rate **UPDATE**

I'm trying to work up a good load for my Remington 700 SPS Varmint .308.

The bullets I have are 178 gr., 168 gr., 165 gr, and 150 gr.

What would be the best bullet for a 1:12" twist rate barrel?

Also, will a load recipe that was shot through a 1:10" barrel be ok for the 1:12" barrel?


Last edited by riverwalker76; March 12, 2010 at 05:58 PM. Reason: Update content
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Old March 12, 2010, 08:01 PM   #2
riverwalker76
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Any takers?
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Old March 12, 2010, 09:06 PM   #3
Brian Pfleuger
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You need to measure the lengths of your bullets then go here and enter the appropriate info.

JBM may, in fact, have the bullet lengths in their database


As for a 1:10 load fired in a 1:12 gun, I assume that you mean will there be a pressure problem? Reasonable changes in twist rate do not normally effect pressure to an appreciable degree in typical "civilian" firearms. Regardless, 1:12 is less than 1:10 so the pressure would be LOWER, if anything.
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Old March 12, 2010, 09:32 PM   #4
riverwalker76
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I'm not worried about pressures.

I'm worried about which bullet would be the most accurate in my barrel.

For instance ... some rifles like lighter bullets while others like heavier bullets. I didn't know if there was a correlation between rifling and bullet stability.

Thanks for the websites.
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Old March 12, 2010, 09:37 PM   #5
Brian Pfleuger
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Alrighty, well, in that case those two links will be your friend. I assume that you have a set of calipers to measure the bullet length, which would be better than relying on the database. The loads listed will be close enough to the correct speed to give you an idea of stability using the calculator. After that, you'd have to poke holes in paper to say for sure which of the stable load combinations will shoot better in your gun.


I believe that you'll be fine with the 3 lighter bullets but may have trouble stabilizing the 178gr.
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Last edited by Brian Pfleuger; March 12, 2010 at 09:42 PM.
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Old March 12, 2010, 09:52 PM   #6
Jim243
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Quote:
I'm worried about which bullet would be the most accurate in my barrel.
That is a completely different can of worms! You asked in your post about twist rate (stabilization). Accuracy is more dependent on your rifle and how it is set up. Bullet type & mfg not just weight. What range are you shooting? Is your rifle bedded. Are you shooting sighters or just single for hunting? Depending on range, what are the wind conditions? How long is your barrel(20 inch or 22 inch or 24 inch)?

Also which powder you use is going to be a factor. Are you setting your oal to be on the line & grooves or are you going to use a 0.020 inch jump.

Actually here is a better place to go to get your answers.

http://www.6mmbr.com/308Win.html

Jim
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Old March 12, 2010, 09:52 PM   #7
riverwalker76
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I punched in the 178 gr. and it came out at 1.433 on the Miller Scale. Is that good or bad? I'm going by the military standard of 1.3 - 1.5 vs. his standard of 1.3 - 2 .
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Old March 12, 2010, 09:57 PM   #8
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The rifle is a 26" free floating barrel. Bedded action, and I am using a US Optics SN-9.

Wind conditions would be 3 - 5 mph and distance is 500 yds.

Powder is either Benchmark or IMR 8208 XMR.

I like to practice out to 500 yds. so that I can easily shoot below that during deer and elk season.

I guess what I'm asking, and I don't mean to confuse you all, is this ......


If I have a worked load that is known to be exceptionally accurate in a DPMS Md. LR-308, 24" barrel, 10" twist could I attempt the same cartridge in my Remington 700 SPS Varmint .308, 26" barrel, 12" twist With similar results?

Last edited by riverwalker76; March 12, 2010 at 10:05 PM.
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Old March 12, 2010, 10:05 PM   #9
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Wind doesn't look like a factor, 500 yards, you are best off using the 168 grain bullet for your twist rate and distance. Not sure how stable the 178 .
will be but it could go to sleep at 200 yards out. (which is good).

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Old March 12, 2010, 10:17 PM   #10
riverwalker76
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By " going to sleep" do you mean .... hitting the dirt or stabilizing? Which do you mean?

So ... are you also stating that I should stay between 150 & 168 gr. on a bullet at that distance?
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Old March 12, 2010, 10:44 PM   #11
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s=1.433 is an excellent number. Harold Vaughn likes 1.4 best. Don Miller likes 1.5 best, so you are in the slot. Rotation slows more gradually than frontal velocity, so the bullet gets more stable as it travels.

Going to sleep means the slightly helical path caused by bullet jump at muzzle exit and the settling of coning motion of the tip has completed and the thing is flying with its best, most settled configuration. That produces best accuracy. You'll find, in general, that flat base bullets are disturbed less at muzzle exit than bottails, so they give the best accuracy in the 100 to 300 yard (when there is no wind) range. Beyond that the boattails win.
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Last edited by Unclenick; March 13, 2010 at 03:50 PM. Reason: typo
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Old March 12, 2010, 10:55 PM   #12
Jim243
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Yes - Stablizing

Yes - 150 to 168 grains

It is a trade off - weight for speed (fps).


Jim

What unclenick said.
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Old March 13, 2010, 01:26 AM   #13
Zak Smith
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In my 1:12 (24"- AWP), I have shot 125's up to 210's with excellent accuracy. My long-range match load is a 155 Lapua Scenar at about 2920 fps.
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