Shelldrake
CGN frequent flyer
- Location
- Right behind you,,
.308 question
- Thread starter OctaRon1
- Start date
And 1:10 for 200 and up.
paperslayer
Regular
- Location
- Chilliwack
Bull. 12 twist is more than enough.
paperslayer
Regular
- Location
- Chilliwack
There is a ton of CGN internet bulls*it that says you need 10 twists for anything over 168 grains. Absolute crap. 12" twist in a .308 will shoot anything. German Salazar tested 13 twists in a 30-06 and found they worked amazingly well for 200 grain Sierras
I agree. It's not just CGN, but internet BS.
One person says it, and it gains ground till most think it's true. I was continually told 1:12 up to 168's, 1:11.25 is around 185's, and 1:10 for 185+.
I bought 208 and went for it. Not a single issue at 1000yards. I've rang the 12" gong at 1000 4/5 shots before in moderate wind, and last weekend in windy (gusty) conditions 5/5 at a 10" at 850.
If my bullet was tumbling, it wouldn't be that precise. That's not much to brag about but proves the "tumbling projectile" theory is BS. I'm not a great shooter by any means and have only been shooting 3/4 of a year. (~1500 rounds)
This weekend is 12" at 1200. Stoked!
Much of the bullet weight vs twist rate confusion is a simple matter of perspective. You can “shoot” a 240 grain bullet from a 308 with a 14 twist, but don’t expect to win any accuracy contest with it… I mean... it will go bang for ya but accuracy will be, lets say... less than ideal.
There are a number of factors that drive the “ideal” twist rate for each bullet that include altitude and temperature as they both influence air density. Dense air needs more spin to maintain stability.
I’ve shot extremely well at 300-500 yards using Berger 185s and a 13 twist. But day to day it was just not consistent especially at 800-1000. I have since rebarelled to a 1:11 and my long range shooting has improved significantly with 185s and I can run heavier if I want.
The moral of the story is to err on the side of a faster twist so you can run the heavier rounds without having to drive them too hard.
Oh ya – to that point – not fair to drag 30-06 into a discussion of barrel twist rates for a 308. A 30-06 goes faster so it can get by with a slightly slower twist rate than a 308.
There are a number of factors that drive the “ideal” twist rate for each bullet that include altitude and temperature as they both influence air density. Dense air needs more spin to maintain stability.
I’ve shot extremely well at 300-500 yards using Berger 185s and a 13 twist. But day to day it was just not consistent especially at 800-1000. I have since rebarelled to a 1:11 and my long range shooting has improved significantly with 185s and I can run heavier if I want.
The moral of the story is to err on the side of a faster twist so you can run the heavier rounds without having to drive them too hard.
Oh ya – to that point – not fair to drag 30-06 into a discussion of barrel twist rates for a 308. A 30-06 goes faster so it can get by with a slightly slower twist rate than a 308.
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Faster twist rates actually improve the lethality - or terminal ballistics. This is a point rarely mentioned in popular hunting discussion. Usually the focus is on foot pounds as derived simply from velocity and bullet weight. The spin rate is also a significant factor.
I like to think of it as the speed of a propeller blade causing more damage if it spins faster. However the physics is calculated this does have an effect. Another way to think of it is fast twist barrels can cause bullets to explode in flight. Just under the ragged edge of self destruction the bullet will explode on impact causing fragmentation damage.
I like to think of it as the speed of a propeller blade causing more damage if it spins faster. However the physics is calculated this does have an effect. Another way to think of it is fast twist barrels can cause bullets to explode in flight. Just under the ragged edge of self destruction the bullet will explode on impact causing fragmentation damage.
Tactical applications tend to use match or FMJ bullets that don't expand (military can't due to the Geneva Convention, police favor stuff like FGGM), so there isn't really anything to cause a propeller blade effect after impact. Some bullets are designed specifically to tumble on impact (creating a larger wound channel) to get around that. Bullets used in mil/tac applications, when fired out of a 308 aren't going anywhere close fast enough to making them explode. Especially not thick jacketed match or FMJ bullets. Those same bullets get fired out of 300WM's with faster twist barrels.
As far as supersonic performance goes, faster twist rates give you guaranteed stability in extreme cold.
As far as supersonic performance goes, faster twist rates give you guaranteed stability in extreme cold.
It's not that bullets are designed to tumble, it's the delicate combination of bullet selection, twist rate and muzzle velocity that cause that - and the thickness of whatever you are shooting at. A bullet will tumble on impact because it is under stabilized or became under stabilized as it passes through the body. It will be under stabilized because the twist rate is too slow or slowish for the velocity. In this case on impact the bullet can take on a path that may deviate from the direction of travel.
My statement regarding fast twist barrels is largely based on my experience in the old days when we were permitted to hunt in Canada with AR15s, which I did almost exclusively for years (the good old days). I had 3 of them and 2 had the new (at the time) 7 inch barrel twist rates. I also had a couple other rifles in 223 with 9 and 13 inch twist rates. From experience with these rifles I can tell you with absolute certainty that bullet performance varies significantly based on the barrel twist rate.
I can recall shooting many animals in rapid succession with 55 grain FMJs and 7 inch twist at ranges of 50 yards where the animal after being struck several times still managed to run off. The same rifle using 69 grain SMKs would literally explode animals as though struck by lightening. In this comparison it was clear that the over stabilized FMJ poked a nice clean hole and given the thickness of that particular animal did not begin to tumble. Perhaps a thicker animal would have created a situation where the bullet would have tumbled and dumped its energy. The same FMJ would be reasonably effective on the same animals from the 13 twist barrel - I figure because they were under stabilized.
In the case of the 69 grain SMK which is not as rigid a bullet as a FMJ - on impact they were explosive. While many people feel a 223 is not enough gun for a deer - I have evidence to the contrary. 69+ grainers and a 7 twist is good business on deer.
That same 7 twist rifle could not be used to shoot 40 grain bullets because they exploded in the air at about 50 yards.
Now even in the case of a 308 you can have bullets explode if the bullet is light enough, the twist rate fast enough and velocity high enough. Guys do experiment with 230 grain bullets from a 308 using 1:6.5 twist rates. Now if a guy was to fire a 120 grain bullet at over 3100 FPS - I would not be surprised if his bullets frequently fail to reach the target. The ones that do however will hit like hand grenades.
My statement regarding fast twist barrels is largely based on my experience in the old days when we were permitted to hunt in Canada with AR15s, which I did almost exclusively for years (the good old days). I had 3 of them and 2 had the new (at the time) 7 inch barrel twist rates. I also had a couple other rifles in 223 with 9 and 13 inch twist rates. From experience with these rifles I can tell you with absolute certainty that bullet performance varies significantly based on the barrel twist rate.
I can recall shooting many animals in rapid succession with 55 grain FMJs and 7 inch twist at ranges of 50 yards where the animal after being struck several times still managed to run off. The same rifle using 69 grain SMKs would literally explode animals as though struck by lightening. In this comparison it was clear that the over stabilized FMJ poked a nice clean hole and given the thickness of that particular animal did not begin to tumble. Perhaps a thicker animal would have created a situation where the bullet would have tumbled and dumped its energy. The same FMJ would be reasonably effective on the same animals from the 13 twist barrel - I figure because they were under stabilized.
In the case of the 69 grain SMK which is not as rigid a bullet as a FMJ - on impact they were explosive. While many people feel a 223 is not enough gun for a deer - I have evidence to the contrary. 69+ grainers and a 7 twist is good business on deer.
That same 7 twist rifle could not be used to shoot 40 grain bullets because they exploded in the air at about 50 yards.
Now even in the case of a 308 you can have bullets explode if the bullet is light enough, the twist rate fast enough and velocity high enough. Guys do experiment with 230 grain bullets from a 308 using 1:6.5 twist rates. Now if a guy was to fire a 120 grain bullet at over 3100 FPS - I would not be surprised if his bullets frequently fail to reach the target. The ones that do however will hit like hand grenades.
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You can explode any bullet if you adjust thing to extremes but your chances of blowing up a 155-185gr heavy jacketed bullet with a common .300/.308 10 twist barrel are pretty slim. The twist rate was not selected with that effect in mind.
paperslayer
Regular
- Location
- Chilliwack
for a given powder load and bullet weight, a faster twist will result in less terminal energy. Faster twists result in more torque which affects precision. buy what you want and say what you want but the truth is nobody "needs" anything tighter than a 12 twist.
Chinbullco
Regular
- Location
- NW Alberta
Never built a rifle out of need. Just ordered a 1:8 1.25" diameter .3075" to finish at 19/20". It's only requirement will be to shoot one mile. It may or may not work but finding out is the entertainment value I'm looking for. If we all had the same barrel twist, same receiver, same trigger, shot the same bullets, used the same sights, we would be as boring as short range benchrest shooters. Non-diversity sucks.
paperslayer
Regular
- Location
- Chilliwack
.3075" is a palma bore. Too tight for anything more than 156 grain bullets, and only 240 grain bullets would need an 8" twist. I would never order a barrel in those dimensions.
Chinbullco
Regular
- Location
- NW Alberta
I have a couple 30 cal barrels with .3075 bores and 1:12 twists, and they shoot the 155's great, but they shoot the 205's fantastic. Accuracy improved as bullet weight increased. An interesting paragraph in Litz' "Applied Ballistics" mentions quick twist barrels may develop increased velocities due to the bullets increased resistance in the bore. In other words the high pressure/time span is increased. Anyhow I get your point, I hope you understand mine.
paperslayer
Regular
- Location
- Chilliwack
This is off the Krieger website
"We only offer the .30 "Tight" caliber barrels up to a 1-12 twist. The reason being, we have seen pressure issues arise when using heavy, long bearing surface bullets in this tight bore/tight groove configuration. We strongly suggest against using bullets heavier than 175 grain, and/or magnum pressure cartridges in any .30 Tight caliber barrels due to the dangers of high pressure and the increased chance of copper fouling."
"We only offer the .30 "Tight" caliber barrels up to a 1-12 twist. The reason being, we have seen pressure issues arise when using heavy, long bearing surface bullets in this tight bore/tight groove configuration. We strongly suggest against using bullets heavier than 175 grain, and/or magnum pressure cartridges in any .30 Tight caliber barrels due to the dangers of high pressure and the increased chance of copper fouling."
