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Old April 14, 2012, 09:11 PM   #1
rebs
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barrel twist and bullet weight ?

with the 1 in 7, 1 in 8, and 1 in 9 twist, what bullet weights work best with what twist ?
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Old April 14, 2012, 09:37 PM   #2
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I'll assume you are talking about 223 Remington. With faster twist rates you get the ability to stabilize longer bullets but may lose the ability to shoot the very lightly constructed varmint bullets (which can tend to tear apart after leaving the barrel). But I've seen people shoot 55 grain FMJ and SP bullets in all twist rates with good results.

There is just a lot more to a good load than the length of the bullet (which is what matters for twist rate, not the weight). So while it can certainly matter if you are wanting to shoot either extreme in bullets, it doesn't always matter. But then again I mostly plink and shoot 3 gun so for me its more about shooting skill than fractions of MOA accuracy difference.
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Old April 14, 2012, 09:43 PM   #3
farmerboy
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Google "Lilja twist rate". They make fine barrels and I use this chart to get me there.
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Old April 14, 2012, 10:08 PM   #4
Archie
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Twist rate

Rate of twist needed to stabilize a bullet is based on bullet diameter vs. bullet length. Of course, the bullet cannot get longer without getting heavier (normally).

One in Seven for .223/.224 diameter bullets is considered 'fast' and will stabilize longer, heavier bullets. Somewhere around 80 grains is about as heavy as .22 caliber bullets go, to my recollection.

As Adamantium said, one can have a twist too fast for a given bullet. In .22s, the lighter bullets - 35 to 40 grains - are usually built for something on the order of .22 Hornet, which doesn't go as fast as .223 Remington or .22-250 for comparison. But .22 Hornet bullets are constructed lightly, to expand at the lesser velocities. So, at high speed and over spun, they tend to destroy themselves by centrifugal force.

However, with bullets designed for .223 Remington, that's harder to do.

In terms of accuracy, a whole lot of over-spin is better than just a little bit of under-spin.
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Old April 15, 2012, 01:56 PM   #5
Jimro
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Assuming that the barrel length is the same 20" as on a standard AR service rifle...

1:9 shoots up to 69gr HPBT bullets very well, some can shoot 75gr HPBT well

1:8 shoots 80gr HPBT for single load stages, usually 77gr HPBT for "across the course"

1:7 the "milspec twist" shoots 80gr HPBT well, handles 77gr HPBT no problem, but isn't fast enough for 90gr HPBT

Anything 1:8 or tighter is fine for High Power matches. 1:9 is doable, but I only know one person who has done it (and he shoots High Master scores with 69gr SMKs) but is also a .mil sniper in his day job.

If the barrel length changes, then all bets are off. A lot of competitors like a 1:7.8 twist because it stabilizes the 80 grainers a tad better than the 1:8 twist without introducing "bullet imbalance" on the target like a 1:7 can. For the same bullet a 1:8 twist will introduce almost a tenth of an inch less variation on target due to bullet imbalance.

If you have a different barrel length or cartridge combo in mind, let us know.

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Old April 20, 2012, 02:16 PM   #6
rebs
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Thank you for the replies, I appreciate it
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