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Slow twist hurts ballistics!
- Thread starter Savage99
- Start date
A slow twist may be just fine if the bullet length is short and/or the muzzle velocity is high.
If the twist is TOO slow the ballistics will be degraded. A marginally stabilized bullet will wobble more than it should which will make it less aerodynamic than a properly stabilized bullet.
If the twist is TOO slow the ballistics will be degraded. A marginally stabilized bullet will wobble more than it should which will make it less aerodynamic than a properly stabilized bullet.
The Berger site told me that shooting a .22 cal 77gr bullet down a 24" 1-9" twist would be "unstable". I proved this theoretical caculation to be false in my situation. I loaded up 77gr SMK's with 24.4 grains of W748 and this load yielded about 2750 fps. Took this load all the way out to 600 yards with perfect bullet stability using my AR15 varmint. So dont be dead sold on internet theoretical comments. Take a safe approach, load up some test rounds and try.
"You may shoot good groups under these conditions, but the BC of the bullet will not be optimized."
The BC may not be optimized but still quite acceptable. A wobbling bullet (especially a long one), will induce more drag and be less aerodynamic. This may become a factor only at extreme range.
The BC may not be optimized but still quite acceptable. A wobbling bullet (especially a long one), will induce more drag and be less aerodynamic. This may become a factor only at extreme range.
Mosin-Marauder
New member
My 1-9 likes almost all 55 Grainers and 62 Grainers, I tried some Gorilla Ammo 55 Grain Blitzkings the other day though and they didn't shoot well at all.
Txhillbilly
New member
I shoot 75 grain BTHP match out of my 1-9 twist Savage 12 223 all the time. The bullets are very stable. Not so much with the longer 75 grain A-Max bullets.
The OP should have included a little more info to prevent confusion. On the Berger site there is a link to input data and determine the best twist.
http://www.bergerbullets.com/twist-rate-calculator/
I think this is what he is referring to. The results he got indicate his bullet/barrel combo is marginal. For normal shooting a most of us will do just fine with marginal or even slightly unstable. It is only at extreme ranges where the ideal stability starts to be a big deal
http://www.bergerbullets.com/twist-rate-calculator/
I think this is what he is referring to. The results he got indicate his bullet/barrel combo is marginal. For normal shooting a most of us will do just fine with marginal or even slightly unstable. It is only at extreme ranges where the ideal stability starts to be a big deal
I don't think I'd try to argue with the Engineers of Berger. They don't do their testing by shooting long bullets in slow twist guns at 100 yard targets.
You may up the velocity and get the bullet to work at 100 yards, but step out to 600 and see what happens.
An example the Army determined the M16A1 (1:12) lost it shooting M855 (62 gr) short of 100 yards.
I cant get anything heavier then 55s to shot out of my SP1 (AR 1:12) at 100 so tried it in my Rem M-700 1:12, I increased the velocity where I could get groups. Or thought I could get groups until I got a bolt gun in 1:7. Then I saw the difference.
You step out to 300 you see a real distance. You'll also find the 1:7 shoots the lighter 52-55 gr. bullets.
But too really see the distance step out to 600 or even 1000 yards.
Back to Berger:
First its not the weight of the bullet, but the length. To give you an idea Berger says their 64 gr with a 1:12 our of a 24 in barrel, I don't doubt them, I never tired but its a short FB bullet, .815".
Compare that with the Barnes 62 gr bullet. Lighter but at .973 its longer. Berger in testing this bullet says it needs a min. of 1:9.
If one is going to error, error on the side of faster twist. If you insist on shooting heavier bullets on your slower twist guns, pick your bullet by length.
You can get shorter bullets if you forgo the Boat Tails and stick with flat based bullets.
If you want to shoot Bergers you need to understand how they work. They are designed to enter the animal a few inches and then come apart destroying the nervous system of the animal. To work properly you need centrifugal force the faster twist gives you. You also need velocity. Berger engineers told me that the remaining velocity of 1800 fps.
If you do go slower twist, you need to find a bullet designed to hold together.
You may up the velocity and get the bullet to work at 100 yards, but step out to 600 and see what happens.
An example the Army determined the M16A1 (1:12) lost it shooting M855 (62 gr) short of 100 yards.
I cant get anything heavier then 55s to shot out of my SP1 (AR 1:12) at 100 so tried it in my Rem M-700 1:12, I increased the velocity where I could get groups. Or thought I could get groups until I got a bolt gun in 1:7. Then I saw the difference.
You step out to 300 you see a real distance. You'll also find the 1:7 shoots the lighter 52-55 gr. bullets.
But too really see the distance step out to 600 or even 1000 yards.
Back to Berger:
First its not the weight of the bullet, but the length. To give you an idea Berger says their 64 gr with a 1:12 our of a 24 in barrel, I don't doubt them, I never tired but its a short FB bullet, .815".
Compare that with the Barnes 62 gr bullet. Lighter but at .973 its longer. Berger in testing this bullet says it needs a min. of 1:9.
If one is going to error, error on the side of faster twist. If you insist on shooting heavier bullets on your slower twist guns, pick your bullet by length.
You can get shorter bullets if you forgo the Boat Tails and stick with flat based bullets.
If you want to shoot Bergers you need to understand how they work. They are designed to enter the animal a few inches and then come apart destroying the nervous system of the animal. To work properly you need centrifugal force the faster twist gives you. You also need velocity. Berger engineers told me that the remaining velocity of 1800 fps.
If you do go slower twist, you need to find a bullet designed to hold together.
I shoot 75 grain BTHP match out of my 1-9 twist Savage 12 223 all the time. The bullets are very stable. Not so much with the longer 75 grain A-Max bullets.
My Howa 1:9 twist shoots 69gr Sierra MKs the best; always sub 1/2 MOA and sometimes better than 1/4 MOA.
It also shoots SOME 75gr OK, but not always sub 1/2 MOA. Similar to your gun, mine won't shoot the 75gr A-Max worth a darn.
It's the same with 55gr or lighter bullets. They shoot OK, but not great; i.e. often sub 1/2 MOA but not always.
All I know is that each gun is different, but there are certainly many 1:9 twist barrels which are quite good with 69gr bullets.
Bryan Litz tests BC of Nosler Long Range Accubond Bullets.. Savage99 this might help you understand what you were reading at Berger's web site. Brian used to be the head ballistician for Berger and probably helped write the stability program you used.
"...a link to input data and determine the best twist..." Yep and it appears to be entirely theoretical by some programmer. Their bullet list gives twist ideals that are at odds wit the rest of the world too. May be something in the construction of their bullets, but 1 in 19 for a .30 Cal. 115 grain bullet or 1 in 15 for a 150, 1 in 14 for a 155 and 1 in 13 for a 168 is decidedly, um, unusual. Don't know of any barrels made with any of those twists.
Marginal stability means only that you are in the gray area between known good and known bad.
It doesn't mean that a bullet will shoot good or bad. It doesn't mean that it won't change based on conditions in the field (the reason the Army left the 1:14 twist for a 1:12 twist on the M16A1).
Too fast a twist can amplify bullet imbalance, so a properly stabilized bullet may shoot no more accurately than a marginally stabilized bullet. Or it may shoot better, or worse.
It may be rocket science, but there are some things you just have to try for yourself.
It doesn't mean that a bullet will shoot good or bad. It doesn't mean that it won't change based on conditions in the field (the reason the Army left the 1:14 twist for a 1:12 twist on the M16A1).
Too fast a twist can amplify bullet imbalance, so a properly stabilized bullet may shoot no more accurately than a marginally stabilized bullet. Or it may shoot better, or worse.
It may be rocket science, but there are some things you just have to try for yourself.
T. O'Heir said:"...a link to input data and determine the best twist..." Yep and it appears to be entirely theoretical by some programmer. Their bullet list gives twist ideals that are at odds wit the rest of the world too. May be something in the construction of their bullets, but 1 in 19 for a .30 Cal. 115 grain bullet or 1 in 15 for a 150, 1 in 14 for a 155 and 1 in 13 for a 168 is decidedly, um, unusual. Don't know of any barrels made with any of those twists.
Obviously you don't shop for custom barrels much, as almost all the so called unusual twists are available from a majority of barrel makers. Lilja, Krieger, Pac-Nor, and others have twist rates as slow as 1:17 and 1:18 in .30 calibers. Now these twist rates are not commonly used in commercial rifles, but for competition shooters they rarely use standard twist barrels.
May be something in the construction of their bullets, but 1 in 19 for a .30 Cal. 115 grain bullet or 1 in 15 for a 150, 1 in 14 for a 155 and 1 in 13 for a 168 is decidedly, um, unusual. Don't know of any barrels made with any of those twists.
Just to point out normal uses for those twists...
1:19, 30 Benchrest cartridge. Shoots flat based light for caliber match bullets fast for 200 yard and less benchrest competition. Twist rates generally range 1:16 to 1:19 for this rather specialized endeavor...
1:14. Palma or Fullbore competition (international Palma requires 155 or lighter projectiles)
1:13 Parker Hale M85/C3 sniper rifle. (twist rate ranged 1:13 to 1:14 depending on what barrel you got, the rifles were designed to fire 144~147gr FMJ bullets accurately).
Most 30 cals on the market today are 1:10, save for the 30 Blackout, which has made 1:8 a popular choice for the heavy subsonic loads, and "tactical" rifles which go 1:11, 1:11.25 or 1:12 depending on manufacture (although plenty also use the standard 1:10).
4runnerman
New member
I have a Savage FVSS Model 12 in 223. It has a 1-9 twist. Shoots 75 A-Max real nice out to 600 yards. Never have pushed it further then that as I feel that is about all you can expect out of a 223. My normal load is 60 A-Max, but have also shot 69 Serria with great accuracy too.
I don't know how many people here have read Bryan litz's book but, he explains stability, marginable... Bergers calculator is not a dead nuts calculation.
There's even different models for different types of bullets. Measure a 40 grain vmax bullet and use it in their calculator and see what it's SG factor is with a 14 twist. How many if you guys have shot 40 gr bullets in a 14 twist, it works for me.
4runnerman- I heard there was a match in grand forks last weekend, did you go?
There's even different models for different types of bullets. Measure a 40 grain vmax bullet and use it in their calculator and see what it's SG factor is with a 14 twist. How many if you guys have shot 40 gr bullets in a 14 twist, it works for me.
4runnerman- I heard there was a match in grand forks last weekend, did you go?
if you want heavy and you are having issues with berger/sierra's, the Hornady 75gr HPBT is significantly shorter than both, and the same goes for their 68gr vs SMK 69gr. maybe someone can correct me, but does the balance of the bullet have anything to do with contradicting the length. like if the base is bottom heavy versus others in the same weight/length, does that make a difference? I ask because of the polymer tipped Hornady 75gr amax, obviously the poly tip makes it longer, but since little weight is in the poly tip, does it matter?