The issue with those that are match shooting 308's with an over-twisted barrel, is TORQUE. FTR and Palma shooters generally use 30" barrels. That excessive torque throws an 18 pound rifle around pretty damned good on a harris bipod, not to mention off your elbows. That affects accuracy far more than spin drift.
Best twist rate for 155 Lapua - 308 Win
- Thread starter fclassguy
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Boomer, I think you and I could be great friends.
I've been preaching that serman for 30 years.
Terminal energy is only calculated in terms of foot pounds... velocity times weight, but with no regard for the RPMs introducing explosive fragmentation. Just under the ragged edge of destruction is where you want to be.... but thats for hunting
For accuracy it is my understanding that the slowest twist that WILL stabalize the bullet will be most accurate.
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I can only speak to my own experience, but I have not been aware of the combination of a fast twist and heavy bullets making my .308 more difficult to shoot or control from the bipod. But perhaps I'm sufficiently hardened to heavy recoiling rifles that I don't notice difficulties of torque induced recoil from a 20+pound .308 or perhaps my steel PH bipod isn't as springy as the Harris. I do have a Harris on my .243 and it seems stable enough when shooting 95 gr Lapuas, although when using a bipod I do my best to choose a suitable firing point where I can use it without extending the legs.
One stunt I could manage on a calm day with my Gaillard 1:7 .222 loaded with 52 gr MKs and sighting through a 12X scope was to cut a 3/16 chain from 100 yards, and I could call which side of the link I would cut first, and yes given cam conditions I could do this on demand from prone. This was accuracy I could see. Paper groups were small enough that measuring them accurately was beyond my ability, as the results from measuring the outside diameter of the group and subtracting the diameter of the bullet resulted in a number too small to be believable.
I maintain that any given rate of twist will stabilize a wide range of bullet lengths and weights, and that by choosing a slow twist you limit yourself to a smaller range of bullets the rifle is capable of shooting competitively. I will concede though that my experience flies in the face of shooters with much more experience than I have. Perhaps, for instance, I stumbled accidently on just the right variables of linear and rotational velocity which combined to produce a rigid axis, so perhaps what I experienced with the .222 and the .308 could not be duplicated with a .22-250 or a .300 magnum. But Brian Litz suggests on page 150 of his book, "As it turns out, the effect that the increased velocity has on rigidity of the spinning mass is slightly greater than the effect of strengthening the overturning aerodynamic torque . . . " Further down the page he goes on to explain that rotational velocity which strengthens the axis of rotation declines much more slowly than does linear velocity which produces aerodynamic overturning torque, thus the bullet stability increases with range.
One stunt I could manage on a calm day with my Gaillard 1:7 .222 loaded with 52 gr MKs and sighting through a 12X scope was to cut a 3/16 chain from 100 yards, and I could call which side of the link I would cut first, and yes given cam conditions I could do this on demand from prone. This was accuracy I could see. Paper groups were small enough that measuring them accurately was beyond my ability, as the results from measuring the outside diameter of the group and subtracting the diameter of the bullet resulted in a number too small to be believable.
I maintain that any given rate of twist will stabilize a wide range of bullet lengths and weights, and that by choosing a slow twist you limit yourself to a smaller range of bullets the rifle is capable of shooting competitively. I will concede though that my experience flies in the face of shooters with much more experience than I have. Perhaps, for instance, I stumbled accidently on just the right variables of linear and rotational velocity which combined to produce a rigid axis, so perhaps what I experienced with the .222 and the .308 could not be duplicated with a .22-250 or a .300 magnum. But Brian Litz suggests on page 150 of his book, "As it turns out, the effect that the increased velocity has on rigidity of the spinning mass is slightly greater than the effect of strengthening the overturning aerodynamic torque . . . " Further down the page he goes on to explain that rotational velocity which strengthens the axis of rotation declines much more slowly than does linear velocity which produces aerodynamic overturning torque, thus the bullet stability increases with range.
Bommer said " thus the bullet stability increases with range. "
yes. So when shooters ask about twist to stabalize at long range, they are worrying about a non-problem. If a bullet is stable at 100 yards, then it will be stable at 1000 yards.
But, if a bullet is over-stable, (spinning too fast) it won't nose over as it starts to come down at long range. It stays pointed upwards, as it was when launched. it acts like a gyro. This means it comes down sideways, which is not good for long range shooting.
Many shooters have seen these slashes and egg shaped bullet holes whan marking targets and assumed the bullets were unstable, and needed more twist. In fact, the opposite was true.
But, in the real world, it would take a lab and a lot of testing to see the difference between a 1:14, a 1:12 and a 1:10 on a 155gr bullet.
I had a 1:16 once and it shot the old Sierra palma just fine. It was the optimum twist for the military 147gr bullets.
yes. So when shooters ask about twist to stabalize at long range, they are worrying about a non-problem. If a bullet is stable at 100 yards, then it will be stable at 1000 yards.
But, if a bullet is over-stable, (spinning too fast) it won't nose over as it starts to come down at long range. It stays pointed upwards, as it was when launched. it acts like a gyro. This means it comes down sideways, which is not good for long range shooting.
Many shooters have seen these slashes and egg shaped bullet holes whan marking targets and assumed the bullets were unstable, and needed more twist. In fact, the opposite was true.
But, in the real world, it would take a lab and a lot of testing to see the difference between a 1:14, a 1:12 and a 1:10 on a 155gr bullet.
I had a 1:16 once and it shot the old Sierra palma just fine. It was the optimum twist for the military 147gr bullets.
could be the slash shaped bullet holes were just at long range where the low BC bullets had fallen below the speed of sound and became unstable.
With regard to fast twist, I believe a bit too fast is better than a bit too slow but a faster spinning bullet exagerates and unevenness in the bullets centifugal weight distribution and they are less accurate as a result. That is why the short range bench rest guys can print griuos in the zeros - they shoot short light bullets out of a slow twist - problem is that for long range they move like a fart in the wind
In the case of 308 Win - the case just cant push the really heavy bullets very fast and therefore needs a very fast twist - for the BC to payoff I dont know that its worth it for FTR - neverthe less guys give it a try but I dont see them cleaning up. For my money I preffer to stick with 155s for 308 win
With regard to fast twist, I believe a bit too fast is better than a bit too slow but a faster spinning bullet exagerates and unevenness in the bullets centifugal weight distribution and they are less accurate as a result. That is why the short range bench rest guys can print griuos in the zeros - they shoot short light bullets out of a slow twist - problem is that for long range they move like a fart in the wind
In the case of 308 Win - the case just cant push the really heavy bullets very fast and therefore needs a very fast twist - for the BC to payoff I dont know that its worth it for FTR - neverthe less guys give it a try but I dont see them cleaning up. For my money I preffer to stick with 155s for 308 win
Brutus
CGN Ultra frequent flyer
To the original poster and as Matt has suggested wait for the 1-12 twist (if you can) it will allow you a wider range of bullets to choose from. As an FYI Darin S Cdn and Jeff R USA both were shooting the Berger 185's with great results at this years DCRA nationals.
As to those people who don't think the 1-14 twist will work. I have one and shot the 155 scenars with no issues they measure 1.291 in length. (P.S. so did Russel Simmons of the UK. He was shooting the 155 scenars)
scroll down the page to get his interview
http://fclassuk.webs.com/ftronly.htm
Here is an article from German Salazar about shooting 190 in 1-14 twist at stupid slow speeds
The conventional wisdom among competitive shooters holds that the 1:13" twist barrel is well suited to shooting the 155 gr. bullets and little else - or is it? Some years ago at a 300 Meter ISU match at Fort Benning, Tom Tamas, then the best 300 Meter shooter in the U.S., was shooting next to me with his .30-06 free rifle; naturally we began to talk about it, especially about loads. Tamas told me that his rifle had a 1:14" twist barrel and he was shooting the Sierra 190 at a very low MV, around 2300 fps. This is about the MV level of the famed Frankford Arsenal International Match ammo of the 1920's and 1930's, but that FA match ammo used the 173 gr. government match bullet and was fired in 1:10" twist barrels. Interestingly, Tamas also mentioned that his rifle and load combination didn't shoot very well at all beyond 300 meters. The successful use of the 190 at a low MV and with a slow rate of twist really caught my attention as it was not something that should work based on most shooters' understanding of external ballistics. Yet, notwithstanding conventional wisdom to the contrary, here was Tamas soundly dominating the match with this improbable combination.
http://riflemansjournal.########.com/2010/06/ballistics-heavy-bullets-in-113-twist.html
As to why slower vs. faster twist slower twists reduce RPMs which also equates to less flyers do to imperfections in bullets. ( I don't have to sit in front of e Verna junke machine spinning for unbalanced bullets) Like someone with a 10 twist. Ganderite already explained the nose first issue with faster twist barrels.
As an aside John Lewis set the current 600 yard IBS national record with a hart 1-14 twist barrel shooting 155 Scenars at a eye popping .386 inches.
http://bulletin.accurateshooter.com/2008/04/smith-shoots-amazing-0386-group-at-600/
Trevor
As to those people who don't think the 1-14 twist will work. I have one and shot the 155 scenars with no issues they measure 1.291 in length. (P.S. so did Russel Simmons of the UK. He was shooting the 155 scenars)
scroll down the page to get his interview
http://fclassuk.webs.com/ftronly.htm
Here is an article from German Salazar about shooting 190 in 1-14 twist at stupid slow speeds
The conventional wisdom among competitive shooters holds that the 1:13" twist barrel is well suited to shooting the 155 gr. bullets and little else - or is it? Some years ago at a 300 Meter ISU match at Fort Benning, Tom Tamas, then the best 300 Meter shooter in the U.S., was shooting next to me with his .30-06 free rifle; naturally we began to talk about it, especially about loads. Tamas told me that his rifle had a 1:14" twist barrel and he was shooting the Sierra 190 at a very low MV, around 2300 fps. This is about the MV level of the famed Frankford Arsenal International Match ammo of the 1920's and 1930's, but that FA match ammo used the 173 gr. government match bullet and was fired in 1:10" twist barrels. Interestingly, Tamas also mentioned that his rifle and load combination didn't shoot very well at all beyond 300 meters. The successful use of the 190 at a low MV and with a slow rate of twist really caught my attention as it was not something that should work based on most shooters' understanding of external ballistics. Yet, notwithstanding conventional wisdom to the contrary, here was Tamas soundly dominating the match with this improbable combination.
http://riflemansjournal.########.com/2010/06/ballistics-heavy-bullets-in-113-twist.html
As to why slower vs. faster twist slower twists reduce RPMs which also equates to less flyers do to imperfections in bullets. ( I don't have to sit in front of e Verna junke machine spinning for unbalanced bullets) Like someone with a 10 twist. Ganderite already explained the nose first issue with faster twist barrels.
As an aside John Lewis set the current 600 yard IBS national record with a hart 1-14 twist barrel shooting 155 Scenars at a eye popping .386 inches.
http://bulletin.accurateshooter.com/2008/04/smith-shoots-amazing-0386-group-at-600/
Trevor
There was a thread here somewhere that stated that some shooters were getting good results with Berger 185's in a 13" twist, and one of the links Trevor gave tends to back that up.
Anyone here have any experience with this combination?
Anyone here have any experience with this combination?
Brian Litz recommends 1-12 for Sierra Palma
Very interestingly Brian Litz (Berger's ballistician) recommend 1-12 for Sierra Palma bullet since 1-13 does not stabilize the bullet is worst case.
http://www.appliedballisticsllc.com/Sierra2156.html
People at Berger know a lot about extreme accuracy and their recommendations are :
1-14 for 155.5 VLD
1-13 for 175 VLD
Remember that stability depends on air density, so a guy up in the Rockies can probably shoot 210gr VLD in 1-13 in the middle of summer but the same rifle will fail to shoot accurately 155gr VLD in the middle of winter at sea level
Alex
Very interestingly Brian Litz (Berger's ballistician) recommend 1-12 for Sierra Palma bullet since 1-13 does not stabilize the bullet is worst case.
http://www.appliedballisticsllc.com/Sierra2156.html
People at Berger know a lot about extreme accuracy and their recommendations are :
1-14 for 155.5 VLD
1-13 for 175 VLD
Remember that stability depends on air density, so a guy up in the Rockies can probably shoot 210gr VLD in 1-13 in the middle of summer but the same rifle will fail to shoot accurately 155gr VLD in the middle of winter at sea level
Alex
rnbra-shooter
CGN Ultra frequent flyer
- Location
- New Brunswick
Bryan doesn't say that the 2156 Sierra won't stabilize in a 1-13" twist. His table in the page you cite (BTW good on ya for providing the link!) says that in the worst case a 1-13" twist will give a stability factor of 1.20, and the footnotes explain "*Stability Factor above 1.4 indicates good stability. Below 1.4 indicates marginal stability. Less than 1.0 is unstable."
What this means is that if you have a 1-13" twist, there is an exceedingly good chance that the bullet will stabilize and shoot well. But, if it fails to, you can't say that you weren't warned that there was a small possibility of there being a problem. If you were considering buying a new barrel you might or might not be comfortable ordering a 1-13", perhaps you might want to order a 1-12.5" or 1-12" (personally I'd be happy with any of these, especially since I have shot Lapua 155s, Sierra #2156s and Berger 155.5s out of my 1-13" twist barrel and they have worked well).
Here are the conditions for:
Best case: 1000 feet altitude, 100% humidity, 100 degrees F, and 3000 fps muzzle velocity.
Nominal case: sea level, 50% humidity, 59 degrees F, and 2800 fps muzzle velocity.
Worse case: sea level, 0% humidity, 0 degrees F, and 2600 fps muzzle velocity.
http://www.appliedballisticsllc.com/glossary.html
As I said, I'd rather be shooting high in the Rockies in mid summer!
Alex
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It is a post with some merit. I can tell you that 30 cal shooters spec out WAY too much twist for their bullets when ordering a barrel. I do not have a digital video camera, but I would love to graphically demonstrate what happens to the gun when you put a 175 Sierra in a 13 twist and then shoot the same load in a 10" twist.
Using moderate hold with a Harris, The 13 twist does jump, but use that with a 10 twist and the torque and jump are incredible. You should be using the least amount of twist you can get away with to stabilize a bullet.
Even the 185 LRBT Berger will stabilze with a 13" twist, that is according to Brain Litz.
Tac Shooters universally want 10" twists for their 168 and 175 bullets.... absolutely no idea why....torque affects accuracy!
Remember, it is not weight but bullet length that enters into the formula for required twist rates. There also are many formulas out there that contradict each other a great deal.
Using moderate hold with a Harris, The 13 twist does jump, but use that with a 10 twist and the torque and jump are incredible. You should be using the least amount of twist you can get away with to stabilize a bullet.
Even the 185 LRBT Berger will stabilze with a 13" twist, that is according to Brain Litz.
Tac Shooters universally want 10" twists for their 168 and 175 bullets.... absolutely no idea why....torque affects accuracy!
Remember, it is not weight but bullet length that enters into the formula for required twist rates. There also are many formulas out there that contradict each other a great deal.
For subsonic loads
It is an interesting thread, indeed!. Stabilization can be a strange pursuit. I had a 6.5 barrel in 1-10" twist that stabilized 140 match Sierras just fine [wasn't supposed to, according to the 'experts']
I have a 1-10" twist 30 cal magnum sporter that, despite torque, drives the 180 grain bullets into one small ragged hole. Overstabilized? probably, but I am fine with it. Eagleye.
I have a 1-10" twist 30 cal magnum sporter that, despite torque, drives the 180 grain bullets into one small ragged hole. Overstabilized? probably, but I am fine with it. Eagleye.
I have wondered if this was the case too, but frankly you would need more than a 10 twist for SubS loads. 300 whispers generally need more twist than that.
No, most guys just follow the leader. Many are using Federal Gold Medal ammo and want 10" twists. To each his own...
