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Old August 3, 2010, 11:54 AM   #1
DanThaMan1776
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223 Twist Rate and Terminal Ballistics

This is pertinent to me because my HD firearm is my AR 15.. so I look to get the absolute best terminal ballistics out of it.

My understanding of why 223 rounds fragment is because they yaw to about 90 degrees and the surface area exposed to the force of flesh is maximized and it breaks apart under the pressure. So if the bullet needs to yaw in order to fragment, what causes it to yaw?

Flesh is quite a bit denser than air, so when the bullet impacts the spin rate slows drastically and then the center of gravity in the rear of the spitzer-style bullet swings forward.

It makes sense to me that if you use a slower twist (1:9) as opposed to faster (1:7), the round will slow down faster in flesh and therefore begin to yaw in a shorter distance after impact, thereby increasing the terminal effectiveness of the round.

Am I wrong?
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Old August 3, 2010, 12:02 PM   #2
mete
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Instead of wearing yourself out with numbers , it might not be significant at HD range. Instead get the Federal 40 gr load which will penetrate less than any other load so it's better th for HD and it will do the job.
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Old August 3, 2010, 02:15 PM   #3
Bartholomew Roberts
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Quote:
It makes sense to me that if you use a slower twist (1:9) as opposed to faster (1:7), the round will slow down faster in flesh and therefore begin to yaw in a shorter distance after impact, thereby increasing the terminal effectiveness of the round.

Am I wrong?
It has no practical effect on the terminal effectiveness of the round. The difference between a 1:14 twist and a 1:7 twist is like the difference between 5 million pounds and 5 million pounds with a grain of sand on top of it. The 5 million pounds with the grain of sand on top of it is technically heavier and technically will crush you slightly more than the 5 million pounds; but for practical purposes, it doesn't really matter whether the grain of sand is there.

See this: http://www.razoreye.net/mirror/ammo-...r.htm#twistduh for a more detailed explanation.

Also remember that yawing more quickly, while generally a good thing, isn't always a plus if it reduces penetration past a certain point (for example a .223 40gr HP). There are a lot of factors that can affect bullet performance and many of them are factors you don't have much control over. Luckily, the most important factor is also the one you have the most control over - shot placement.
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Old August 3, 2010, 02:18 PM   #4
thesheepdog
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You want rapid expansion for HD. 55gr HP's are a good compromise for penetration and rapid expansion.
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Old August 3, 2010, 06:40 PM   #5
DanThaMan1776
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That is a very useful link, Bart. Consider the questions answered in full

Thanks a lot, fellas.
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