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Twist Rate Chart?

This is a discussion on Twist Rate Chart? within the Ruger Bolt Action forums, part of the Rifle & Shotgun Forum category; JohnDoe, The twist rate chart is set up by bullet diameter. Your 300 Win Mag shoots .308" bullets so that's the chart you use. Several ...


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Old October 26th, 2010, 08:30 AM   #16
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JohnDoe, The twist rate chart is set up by bullet diameter. Your 300 Win Mag shoots .308" bullets so that's the chart you use. Several cartridges share the same bullet diameter such as a 308 Win, 30-30, 30-'06, 30 Carbine plus many more commonaly known as 30 cals. Not all manufacturers follow the chart but they are always close. In your case, the chart shows 1:10 but your rifle has an actual twist rate of 1:9.5. Your M-77 should stabilize bullets well from 170 to 220 gr.

Optimum accuracy depends on several things with bullet spin rate near the top of the list. Bullet spin is dependent on three attributes ... bullet weight, velocity, and the barrel's twist rate. Because the barrel's twist rate is "fixed", the only way to vary the formula is to use different weight bullets or different velocities. When loading heavy bullets, less powder is used so chamber pressure won't exceed maximum levels, which means lower velocity. With lighter bullets, velocities can be increased by using more powder without exceeding chamber pressure limits.

It turns out that 3000 fps is the optimum velocity for a 1:9.5 twist rate to create the optimum bullet spin rate. That velocity is achieved by using a 180 gr bullet.

Good luck testing your loads and I hope your shoulder holds up to the punishing recoil.



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Old October 26th, 2010, 11:32 AM   #17
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you sir are a book of knowledge, thanks ...

I had found several charts that listed velocity and "punch" over "xx" distances for the .300 and was basing my info from them ...

suppose I will buy several different boxes of 180 gr ... and give them a try first ...

as for the shoulder, lets hope this Hogue stock takes some of the bang outta this baby, it's not too bad with the original boat paddle, but we'll see if it softens some ...

I'll post back after I get some range time setup ...

thanks Iowegan
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Old October 28th, 2010, 01:47 AM   #18
 
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Quote:
Originally Posted by Iowegan View Post
mjr350, Yes, if you just toss a load together from a some source, it may work and it may not. If you use the "factory load" concept, it always works ... then you can tweak a little to optimize. Although there is some merritt in your post ... I truly believe if you stack the odds in your favor, good things will happen. In this case, matching bullet weight to twist rate is an excellent starting point that will result in optimum bullet stability. So ... for JohnDoe's rifle, a 170-200 gr bullet, with the center being 180~190gr. If you start there and take advantage of intense factory ammo testing, you will find the optimum velocity is 3000 fps for a 180 gr and 2900 fps for a 190 gr. I would look at loads in the reloading manual that come closest to emulating factory ammo.
Yea that twist rate chat is a great start to give you a good guideline as to where to start.
For instance, my 22-250 with 1:14 says max 55gr and thats a well known max for a 22cal with a twist rate of 14.
But im not going to take any joe blow's advice on his sweet load unless it falls under the max powder load in my reloading book. Only then after making sure its safe will i certainly take it into consideration.
I should have made my self clearer as there are some loads out there either miss typed or totally out of the ball park. Just research them a little first, thats all im going to advise but thats common sense.
Sorry if i came across a little harsh
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Old October 1st, 2013, 01:33 AM   #19
 
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You might consider the Barnes TTSX in 180. Being homogenous metal, it's longer than a lead core bullet, therefore better BC. The lighter weight provides greater muzzle velocity. These combine to provide a fine long distance round with good terminal performance.
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Old October 1st, 2013, 01:34 AM   #20
 
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Did you ever manage to get access to the twist rate table?
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Old October 1st, 2013, 01:34 AM   #21
 
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I'm still trying
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Old October 1st, 2013, 01:35 AM   #22
 
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Would someone who can access it just post the twist rate for M77s in 300 Win Mag?
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Old October 1st, 2013, 08:51 AM   #23
 
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Quote:
Originally Posted by Frogowar View Post
Would someone who can access it just post the twist rate for M77s in 300 Win Mag?
.308 / 7.62mm 1:15 up to 150 grains
1:14 150 168 grains
1:12 168 170 grains
1:10 170 220 grains
1:8 220 grains or more
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