Is there a negative side to having too fast of a twist rate?
- Thread starter Deja vu
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) and they said only that you may loose some velocity.The muzzle velocity difference between a fast and slow twist is virtually zero.
But too fast a twist can spin bullets too fast, and, with bullets more unbalanced more than others, the centrifugal forces they have will pull them off the muzzle axis when shot; accuracy gets worse. Which is why competitive shooters use a twist as slow as possible for best accuracy. If the rifling engraves the jacket too much weakening it, the jacket will split and fly off the lead core.
But too fast a twist can spin bullets too fast, and, with bullets more unbalanced more than others, the centrifugal forces they have will pull them off the muzzle axis when shot; accuracy gets worse. Which is why competitive shooters use a twist as slow as possible for best accuracy. If the rifling engraves the jacket too much weakening it, the jacket will split and fly off the lead core.
I have never heard of a faster twist shortening barrel life, increasing pressure or anything else. Nor read any cautions about in any reloading databases. While there may be a little, it's masked by the normal 2 to 3 percent spread across powder charges for a given lot number and charge weight.
A 1:11 twist in a 30 caliber barrel has the same rifling angle to bullets as a 1:8 twist in a 22 caliber one. When a cartridge in each burns 1 grain of powder for each square millimeter of bore cross section area, both have equal barrel lives. .308 Win compared to .222 Rem; 3000 rounds each for best accuracy. A .300 Win Mag with a 1:11 twist barrel lasts about 1200 rounds.
People shooting matches with 155's from a 1:14 twist .308 barrel get the same barrel life as one shooting 240's from a .308 with a 1:8 twist. About 3000 rounds each. Those 240's have a much longer bearing area that's engraved by the rifling than the 155's, but it's the hot, high pressure burning powder that wears out the barrels, not the cupronickel jacketed bullets rubbing the rifling on their way in.
A 1:11 twist in a 30 caliber barrel has the same rifling angle to bullets as a 1:8 twist in a 22 caliber one. When a cartridge in each burns 1 grain of powder for each square millimeter of bore cross section area, both have equal barrel lives. .308 Win compared to .222 Rem; 3000 rounds each for best accuracy. A .300 Win Mag with a 1:11 twist barrel lasts about 1200 rounds.
People shooting matches with 155's from a 1:14 twist .308 barrel get the same barrel life as one shooting 240's from a .308 with a 1:8 twist. About 3000 rounds each. Those 240's have a much longer bearing area that's engraved by the rifling than the 155's, but it's the hot, high pressure burning powder that wears out the barrels, not the cupronickel jacketed bullets rubbing the rifling on their way in.
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Bart B is right on. Somewhere I remember seeing a table in relation to this.
A few years ago I picked up a used Savage 10 in .223 to do some groundhog hunting where I live. The rifle had a 1:9 twist.
This was my first faster twist rifle. My first attempt with 50 gr bullets saw groups of 1" at 100 yards. Somehow I just felt the rifle was capable of better.
Second attempt was the Sierra 55 Gr and groups got better, maybe 3/4".
What I found really interesting were the 69 gr Sierra Match bullets, those went into 1 ragged hole.
I spent more time trying lighter bullets in the rifle but I could not duplicate the 69 gr bullets with anything I shot out of it. I've heard others claim they can get very good accuracy out of lighter bullets in a fast twist, I couldn't.
A few years ago I picked up a used Savage 10 in .223 to do some groundhog hunting where I live. The rifle had a 1:9 twist.
This was my first faster twist rifle. My first attempt with 50 gr bullets saw groups of 1" at 100 yards. Somehow I just felt the rifle was capable of better.
Second attempt was the Sierra 55 Gr and groups got better, maybe 3/4".
What I found really interesting were the 69 gr Sierra Match bullets, those went into 1 ragged hole.
I spent more time trying lighter bullets in the rifle but I could not duplicate the 69 gr bullets with anything I shot out of it. I've heard others claim they can get very good accuracy out of lighter bullets in a fast twist, I couldn't.
bamaranger
New member
too fast
I have read and heard of folks driving .22 cal slugs , out of long barreled .223 match rifle, , at high velocity, and the bullets just fragment/mist, and the culprit was thought to be a combination of high velocity and twist.
The phrase, as I remember was either ......"he'd shoot an X or a zero".
The other was Hornet slugs driven at 22-250 & Swift velocities, in humid weather, same result.
I have read and heard of folks driving .22 cal slugs , out of long barreled .223 match rifle, , at high velocity, and the bullets just fragment/mist, and the culprit was thought to be a combination of high velocity and twist.
The phrase, as I remember was either ......"he'd shoot an X or a zero".
The other was Hornet slugs driven at 22-250 & Swift velocities, in humid weather, same result.
Just before Winchester announced they were closing the factory I purchased a model 70 Stealth in .308. It is one of my best shooting rifles and I have no complaints. This rifle has the 1:12 twist. Originally I thought I was going to be handicapped with it being limited to 168 gr bullets. But, that hasn't been the case. It will shoot the Berger 185 gr match to 1000 yards just fine. Now, if I were a good shot I'd be even happier.
Twist is something I wish I had more than just a basic understanding of.
Twist is something I wish I had more than just a basic understanding of.
Bake, benchresters shoot the .30 BR round with 110 to 125 grain bullets in 1:17 or 1:18 twist barrels. And the .308 Win will shoot bullets those weights very accurate with the same twist.
Joed, the US Navy and Air Force Rifle Teams used 7.62 NATO Garands shooting Sierra 190's from 24" 1:12 twist barrels. Won a lot of matches with that load shooting against bolt action match rifles shooting new LC M118 match cases and primers with 44 grains of IMR4320. They easily shot sub 2/3 MOA at 600 yards tested from accuracy cradles and a bit over 1 MOA at 1000. I don't think any AR in .308 has shot that well except maybe the Army Team's AR10's with Berger 185's.
Frankford Arsenal knew the old .30-06's 1:10 twist was too fast for best accuracy with 150-gr. bullets, It did better with the 172-gr. FMJBT bullet. When they designed the shorter barreled M14, they chose a 1:12 twist for its 147-gr. ball bullet leaving about 100 fps slower than the 150's did from the .30-06. That M80 round was more accurate in arsenal test barrels than the M2 .30-06 round with 150's ever was.
Joed, the US Navy and Air Force Rifle Teams used 7.62 NATO Garands shooting Sierra 190's from 24" 1:12 twist barrels. Won a lot of matches with that load shooting against bolt action match rifles shooting new LC M118 match cases and primers with 44 grains of IMR4320. They easily shot sub 2/3 MOA at 600 yards tested from accuracy cradles and a bit over 1 MOA at 1000. I don't think any AR in .308 has shot that well except maybe the Army Team's AR10's with Berger 185's.
Frankford Arsenal knew the old .30-06's 1:10 twist was too fast for best accuracy with 150-gr. bullets, It did better with the 172-gr. FMJBT bullet. When they designed the shorter barreled M14, they chose a 1:12 twist for its 147-gr. ball bullet leaving about 100 fps slower than the 150's did from the .30-06. That M80 round was more accurate in arsenal test barrels than the M2 .30-06 round with 150's ever was.
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Bart B.
While I don't have any actual data to back up my claim, during my research when constructing a fast twist .22-250 I constantly ran into claims from various forums and other sources that a faster twist will shorten a barrels life with all else equal.
It could be just a myth, but it's one of those things that pops up everytime the conservation comes up.
While I don't have any actual data to back up my claim, during my research when constructing a fast twist .22-250 I constantly ran into claims from various forums and other sources that a faster twist will shorten a barrels life with all else equal.
It could be just a myth, but it's one of those things that pops up everytime the conservation comes up.
"Doesn't increased twist also affect pressure, by increasing it slightly?
I'm asking, b/c that was an assumption I had picked up from somewhere."
That is correct but to what extent is hard to prove since variations in bore condition may cause just as much difference between barrels of same twist.
I'm asking, b/c that was an assumption I had picked up from somewhere."
That is correct but to what extent is hard to prove since variations in bore condition may cause just as much difference between barrels of same twist.
In my opinion there is no down side to a fast twist rifle, faster twist opens more doors than a slow twist. I hate being limited on options when it comes to bullets I can use.
Bryan Litz did a test and you can read about it here.
http://bulletin.accurateshooter.com/2015/02/does-barrel-twist-rate-affect-muzzle-velocity-litz-test/
There is about a 5 fps difference in velocity between a 12 and 8 twist .308 Win. Without pressure testing equipment to say for sure I'd be willing to bet the pressure increase if any is very minimal.
Bryan Litz did a test and you can read about it here.
http://bulletin.accurateshooter.com/2015/02/does-barrel-twist-rate-affect-muzzle-velocity-litz-test/
There is about a 5 fps difference in velocity between a 12 and 8 twist .308 Win. Without pressure testing equipment to say for sure I'd be willing to bet the pressure increase if any is very minimal.
My understanding is that an overstabilized bullet tends to keep its original orientation instead of changing its orientation to align with the air flow like an arrow as the path of the bullet changes in its arcing trajectory. This causes the bullet to fly nose high which reduces its effective BC. The bullets don't keyhole but the accuracy is not optimum.
I don't think rifle bullets are shot fast enough in a fast twist often, so there's little evidence that bullets spun to fast keep their spin axes at the launch angle throughout their flight exists. There has been some 22 caliber bullets shot over 5000 fps, but I'm not aware of the twist used and maximum range tested at.
The laws of physics for gyroscopes and other spinning things says bullets spun way too fast will keep their launch angle throughout their flight. They'll appear to keyhole going through the target. If launched at an elevation angle of 1 degree, they'll point 1 degree up going through the paper at any down range point. At 1000 yards, it may not show up as a keyhole. The hole it makes in the paper will be elongated vertically less than .001" more than bullet diameter.
The laws of physics for gyroscopes and other spinning things says bullets spun way too fast will keep their launch angle throughout their flight. They'll appear to keyhole going through the target. If launched at an elevation angle of 1 degree, they'll point 1 degree up going through the paper at any down range point. At 1000 yards, it may not show up as a keyhole. The hole it makes in the paper will be elongated vertically less than .001" more than bullet diameter.
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Tom Matiska
New member
If pushing lighter bullets into the photon torpedo range a fast twist will foul a little quicker. Ratio of shooting fun to copper removal goes down. If you solve the copper problem by soaking overnight with harsh solvents barrel life can go down.
Biggest advantage of over-spinning bullets is very high stability in flight. There are several disadvantages, IME. Most notably,
* Bullets take longer to "go to sleep"
* Increased spin drift at longer ranges
* Bullets can spin apart if not well-constructed
* Bullets are more likely to expand violently when hitting game.
* Bullets take longer to "go to sleep"
* Increased spin drift at longer ranges
* Bullets can spin apart if not well-constructed
* Bullets are more likely to expand violently when hitting game.
A link that illustrates the flight of an over stabilized bullet.
http://www.nennstiel-ruprecht.de/bullfly/fig15.htm
http://www.nennstiel-ruprecht.de/bullfly/fig15.htm