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Twist Rate Effect on Load Data

 
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  #1  
Old 03-16-2013, 12:44 AM
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Twist Rate Effect on Load Data

In nearly every reloading manual I see the test barrel for a 223 Rem is 1:12 twist 24". In my Stevens and by buddies Axis the twist rate is 1:9 twist 22". I would like to know how this will effect the Velocity and the safe max load of the cartridge. I don't want to spin any bullets until the fly apart, but I would like to get as much velocity as I can get accurately/safely.
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Old 03-16-2013, 04:01 AM
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Re: Twist Rate Effect on Load Data

That is difficult to say exactly.
Generally a faster twist will increase pressure a small amount all else being equal .
With factory ammo I can't see that the extra twist will do any harm especially using the longer heavier bullets that may need the extra stability . With very light short bullets in a fast twist you may see some extra precession at long range .
When you reload you are watching the pressure signs anyway and you stop at a sensible load point anyway .
Don't think the 223 has enough powder room to push them too hard but stay away from varmint grenades and very light explosive bullets .
When you have a certain twist rate you should stay with the bullet length and type that suits the twist rate give or take but in the ballpark .
If twist rates were a big factor on safe pressures then the load manuals would be quoting twist rates too .
Just develop a safe load to suit your gun and don't worry too much about what anybody else is doing as it may not be suitable to your gun .
Wether a bullet blows up or not is governed by many factors and you don't know until you run the load /gun combination .
Some of the factors in bullet blow up are.
High pressures for cartridge , High velocities for cartridge , Long barrels , rough barrels , deep "cut rifling " , thin bullet jackets , over hard or very soft bullet jackets , light weight bullets , bullet rotational instability , loose bullet cores , hot burning powders , fast twist rates , tight bore diameters .
Put some of them together and the bullet can explode in the air .
However it would be extremely rare to see so many faults or circumstances in one gun.
Some old Berger bullets were blowing up due to thin jackets , high velocities , deep cut rifling , long barrels , rough barrels , tight bores. Thicker jackets fixed the issue.
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Old 03-16-2013, 08:16 AM
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Re: Twist Rate Effect on Load Data

+1 for Bullet Bumper. Yep...them Aussie's know a thing or two. Probably cause they live upside down. Their brains get more oxygen than ours do. :-)
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Old 03-16-2013, 05:54 PM
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Re: Twist Rate Effect on Load Data

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Originally Posted by azsugarbear View Post
+1 for Bullet Bumper. Yep...them Aussie's know a thing or two. Probably cause they live upside down. Their brains get more oxygen than ours do. :-)
Thanks mate for the kind words. Down here we have to do a lot for ourselves because our arms industry is crap compared to the US . We do make excellent smokeless powders though but not much else for small arms .
If we were really all that smart down here we would be a lot bigger stronger country by now .
We unfortunately have never had people with the foresight , dedication and patriotism of the calibre of John Dickinson, Governor Morris, Thomas Jefferson, John Adams, Thomas Paine, Edmund Randolph, James Madison, Roger Sherman, James Wilson, and George Wythe. Who wrote the Constitution to form our national pride .
My Grandfather was an early settler in Hood River Oregon and I still have his citizenship papers. The wording of the document sends a tingle up my spine , it just exudes patriotism and national pride .
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Old 03-16-2013, 06:36 PM
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Re: Twist Rate Effect on Load Data

My 5.56 M6 has a 16.1" 1:7 RH twist CHF barrel and 55gr bullets don't fly apart coming out of it... I have some 77gr bullets to try next. Being a 1:7 I bet it'll love them.
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  #6  
Old 03-17-2013, 06:49 PM
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Re: Twist Rate Effect on Load Data

Thanks for the responses. I'll just keep at it watching for pressure signs.
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  #7  
Old 03-19-2013, 09:11 AM
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Re: Twist Rate Effect on Load Data

ShowMeShooter,

The effects of twist alone on pressure is negligable, usually on the order of about one-half of one percent. If there's pressure signs appearing, they're coming from other factors within the barrel, chamber or load. Twist alone isn't something to sweat as far as pressure is concerned.

Here's an example; the original M16s were 1x14" twist barrels, which was later changed to 1x12". The standard ammunition (M193) is some fairly warm stuff; 55 grain FMJ @ 3,250 fps from a 20" barrel. When the military upgraded to the M16A4s and M4s, they went to a 1x7" twist, precisely doubling the twist fro the original issue M16s. Yet, the M193 remains in service as training ammo, and there's no problem whatsoever shooting it in the newer, fast twist rifles.

It's not a problem.
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