twist rates

dongun · June 28, 2000, 05:54 PM

In a recent post there was a short discussion on barrel twist rates. I understand that the barrel twist spins the bullet which improves accuracy (and trajectory?). What I'm not sure about is how twist rate effects bullet and powder selection. Can anyone enlighten me? Thanks.

Chad Young · June 28, 2000, 07:39 PM

Well, this is a gross simplification, but, as a rule, heavier and longer bullets require a faster spin rate to stabilize a lighter, shorter bullet in the same caliber.

For example, when the US army switched from a 55-grain .223 projectile to a 62-grain projectile, they had to change the twist rate from 1 in 12" to 1 in 7".

I am sure others here can tell you certaqin twist rates for other calibers.

Southla1 · June 28, 2000, 09:49 PM

Dongun, the twist rate may improve accuracy but not trajectory, only the ballistic co-efficent or the velocity affects trajectory, that is unless the bullet is so unstabilized that it tumbles, then everything goes to hell in a handbasket.
As Chad mentioned the longer heavier bullets in a given caliber require a faster twist rate to properly stabilize them. In some calibers such as 30-06 a midway twist rate is chosen such as 1 in 10. It is not the best for the 110 grainers nor the 220 grainers but does a fair job on both, and the 1 in 10 is optimum for about a 150-170 bullet.
If a bullet is fired in a twist that is too slow it may tumble, in one that is too fast it is overstabalized and will remain in a nose high attitude and do other weird things, that is if it is not spun so fast at such a high velocity that it comes apart right past the muzzle. Some light .224 bullets designed for the 22 Hornet and fired in a 22-250 or a 220 Swift have this happen quite often. It is a combination of the over spin and velocity.

------------------
Carlyle Hebert

Paul B. · June 29, 2000, 06:50 PM

Southla1. I must beg to differ with you on the 1 in 10 inch twist in .30 caliber. Yes it is the standard, but browning used 1 in 12 inches for years in 30-06, and may even still do so. A 1 in 12 inch twist will stabilize a 220 gr. round nose bullet as far as anyone has any business in doing so.
I have 3 rifles in .30 caliber, one 30-06 and two .308's, all with 1 in 12 inch twists. They will all stabilize the heavy bullets to well past 200 yards, which is further than I'd shoot a round nose bullet anyway.
Time constraints keep me from taking this farther, but E-mail me and I'll give you the details.
Paul B.

Southla1 · June 30, 2000, 08:21 PM

Paul, nowhere did I ever say that a 1-12 in a .30-06 will not stabilize a 220 grain bullet. I said it is not the optimum, neither is a 1-10 for that heavy a bullet. I have a very old Rem. 700 22-250 with a 1-14 twist, and yes it will stabalize a 70 grain Speer bullet.....but not very well. The groups are nothing to brag about, but it does stabalize them (sort of). Load it with a 45 or 50 grain bullet even a 52 grain and it is a tack driver! A 1-12 in a 30-06 is about the same way with a 220, yes it works, but about a 1-8 or 1-9 would be better

just like a 1-8 or 1-9 would make that 70 Grain Speer really drive little bitty tacks in my 22-250.

------------------
Carlyle Hebert

OOPS! forgot to add that Husqvarna for years used a 1-12 twist in the 30-05 too.

[This message has been edited by Southla1 (edited June 30, 2000).]
Better make that a 30-06

[This message has been edited by Southla1 (edited June 30, 2000).]

Art Eatman · June 30, 2000, 11:48 PM

And then we can pick flyspecks out of pepper about the length of pointy-nosed boat-tails as compared to flat-based round-noses and and what twist works there.

Whee!

Y'all are both right. Can I go to bed, now, Mommy?

Art

Paul B. · July 2, 2000, 04:49 PM

Southla1. I used the 1/12 220 gr. as an analogy. I have a Kimber in .223 that won't stabilize 60 gr. bullets, and I think it has a 1 in 12 twist. I can't seem to get the rod to twist when I try and check it. The jag holding the patch unscrews, rather than the whole rod turning.
The reason I brought up the 1 in 12/220 thing is every "egg-spurt" in the gun rags says that a 1 inj 12 won't stabilize a 220 gr bullet, and that the .308 won't shoot one (220 gr.) fast enough to do any good. My challenge to them is "WANNA BET?" I have gotten 2350 FPS from a Winchester Mod. 70 with 22" barrel, 1 in 12 twist, and very tight groups. This with both a post-64 push feed and a pre-64 Featherweight. I'll have to try it in a 1 in 10 twist .308 next, when I get time.
Paul B.

Southla1 · July 2, 2000, 05:18 PM

Paul it all boils down to the old saying..........each rifle is a law unto itself. In my young years and not knowing a bit better I decided to glass bed an 03A3 in a Fajan stock. Well I did alright! I bedded the barrel and did NOT do the action! Yea I know now backasswards. Well the damn thing went to shooting 1/2 to 3/4 groups with a full case of 4831 and 190 Match Kings. 5 shot groups that is! By all that was written it should not have been able to hit a barn if fired from inside it. Oh by the way the 4831 is considered to be an overload now! The load was given to me by an old shooter that had been using it ever since he got some of the irst H4831 sold. He never had a problem and I did not either

. I did back off a lil when I got my first manuals. That was almost 40 years ago. Rifle is still bedded wrong and still shooting less than 1 inch

.

------------------
Carlyle Hebert

Hueco · July 2, 2000, 08:06 PM

Alright, I was going to post this question seperately, but it fits in well here.

Say you have a 30 calibre rifle, twist is 1 in 12" and it won't stabalise 220's. What if you up the velocity? Wouldn't the bullet be spinning faster after leaving the muzzle? Would that work? And is this the principle load-development works on?

Hueco

Southla1 · July 2, 2000, 09:23 PM

It may help some Hueco, but the really best way to do it is up the twist (or is it down

? ) Oh hell go to a 1-10 or 1-9

In all seriousness try this site if you have a chance it gives a lot of good info! I am going to ahve to sneak a printer cartridge on the boss (wife) one day and print the whole thing it is a great article, but the pictures will eat up an ink cartridge lol.
http://www.povn.com/~4n6/index.htm

------------------
Carlyle Hebert

Ruben Nasser · July 2, 2000, 09:34 PM

Hueco, yes, increasing the velocity will also increase spinning rate linearly, but in a given caliber you don't have much room to get the 20% increase in velocity needed to compensate from 1 in 10" to 1 in 12", that's why you are restricted from the beginning to a certain range of optimum bullet lenghts (and weight). As Southla1 said, sometimes you get different results in the real world (and nobody knows why...). Load development is a different thing, and is basically selecting components (one bullet, different powders/primers)and trying different combinations until you achieve the results in velocity, consistency, pressure, and accuracy that you desire. Past this you try different seatings depths (and MANY other thigs) to fine tune the load. Look in www.snipercountry.com , there are a couple articles on this.

June 28, 2000, 05:54 PM	#1
dongun Member Join Date: May 7, 2000 Location: Central Arkansas Posts: 76	In a recent post there was a short discussion on barrel twist rates. I understand that the barrel twist spins the bullet which improves accuracy (and trajectory?). What I'm not sure about is how twist rate effects bullet and powder selection. Can anyone enlighten me? Thanks.

June 28, 2000, 07:39 PM	#2
Chad Young Senior Member Join Date: September 20, 1999 Location: Gainesville, FL Posts: 601	Well, this is a gross simplification, but, as a rule, heavier and longer bullets require a faster spin rate to stabilize a lighter, shorter bullet in the same caliber. For example, when the US army switched from a 55-grain .223 projectile to a 62-grain projectile, they had to change the twist rate from 1 in 12" to 1 in 7". I am sure others here can tell you certaqin twist rates for other calibers.

June 28, 2000, 09:49 PM	#3
Southla1 Member In Memoriam Join Date: March 19, 2000 Location: Jeanerette, La. Near the Posts: 1,999	Dongun, the twist rate may improve accuracy but not trajectory, only the ballistic co-efficent or the velocity affects trajectory, that is unless the bullet is so unstabilized that it tumbles, then everything goes to hell in a handbasket. As Chad mentioned the longer heavier bullets in a given caliber require a faster twist rate to properly stabilize them. In some calibers such as 30-06 a midway twist rate is chosen such as 1 in 10. It is not the best for the 110 grainers nor the 220 grainers but does a fair job on both, and the 1 in 10 is optimum for about a 150-170 bullet. If a bullet is fired in a twist that is too slow it may tumble, in one that is too fast it is overstabalized and will remain in a nose high attitude and do other weird things, that is if it is not spun so fast at such a high velocity that it comes apart right past the muzzle. Some light .224 bullets designed for the 22 Hornet and fired in a 22-250 or a 220 Swift have this happen quite often. It is a combination of the over spin and velocity. ------------------ Carlyle Hebert

June 29, 2000, 06:50 PM	#4
Paul B. Senior Member Join Date: March 28, 1999 Location: Tucson, AZ Posts: 3,802	Southla1. I must beg to differ with you on the 1 in 10 inch twist in .30 caliber. Yes it is the standard, but browning used 1 in 12 inches for years in 30-06, and may even still do so. A 1 in 12 inch twist will stabilize a 220 gr. round nose bullet as far as anyone has any business in doing so. I have 3 rifles in .30 caliber, one 30-06 and two .308's, all with 1 in 12 inch twists. They will all stabilize the heavy bullets to well past 200 yards, which is further than I'd shoot a round nose bullet anyway. Time constraints keep me from taking this farther, but E-mail me and I'll give you the details. Paul B.

June 30, 2000, 08:21 PM	#5
Southla1 Member In Memoriam Join Date: March 19, 2000 Location: Jeanerette, La. Near the Posts: 1,999	Paul, nowhere did I ever say that a 1-12 in a .30-06 will not stabilize a 220 grain bullet. I said it is not the optimum, neither is a 1-10 for that heavy a bullet. I have a very old Rem. 700 22-250 with a 1-14 twist, and yes it will stabalize a 70 grain Speer bullet.....but not very well. The groups are nothing to brag about, but it does stabalize them (sort of). Load it with a 45 or 50 grain bullet even a 52 grain and it is a tack driver! A 1-12 in a 30-06 is about the same way with a 220, yes it works, but about a 1-8 or 1-9 would be better just like a 1-8 or 1-9 would make that 70 Grain Speer really drive little bitty tacks in my 22-250. ------------------ Carlyle Hebert OOPS! forgot to add that Husqvarna for years used a 1-12 twist in the 30-05 too. [This message has been edited by Southla1 (edited June 30, 2000).] Better make that a 30-06 [This message has been edited by Southla1 (edited June 30, 2000).]

June 30, 2000, 11:48 PM	#6
Art Eatman Staff in Memoriam Join Date: November 13, 1998 Location: Terlingua, TX; Thomasville, GA Posts: 24,798	And then we can pick flyspecks out of pepper about the length of pointy-nosed boat-tails as compared to flat-based round-noses and and what twist works there. Whee! Y'all are both right. Can I go to bed, now, Mommy? Art

July 2, 2000, 04:49 PM	#7
Paul B. Senior Member Join Date: March 28, 1999 Location: Tucson, AZ Posts: 3,802	Southla1. I used the 1/12 220 gr. as an analogy. I have a Kimber in .223 that won't stabilize 60 gr. bullets, and I think it has a 1 in 12 twist. I can't seem to get the rod to twist when I try and check it. The jag holding the patch unscrews, rather than the whole rod turning. The reason I brought up the 1 in 12/220 thing is every "egg-spurt" in the gun rags says that a 1 inj 12 won't stabilize a 220 gr bullet, and that the .308 won't shoot one (220 gr.) fast enough to do any good. My challenge to them is "WANNA BET?" I have gotten 2350 FPS from a Winchester Mod. 70 with 22" barrel, 1 in 12 twist, and very tight groups. This with both a post-64 push feed and a pre-64 Featherweight. I'll have to try it in a 1 in 10 twist .308 next, when I get time. Paul B.

July 2, 2000, 05:18 PM	#8
Southla1 Member In Memoriam Join Date: March 19, 2000 Location: Jeanerette, La. Near the Posts: 1,999	Paul it all boils down to the old saying..........each rifle is a law unto itself. In my young years and not knowing a bit better I decided to glass bed an 03A3 in a Fajan stock. Well I did alright! I bedded the barrel and did NOT do the action! Yea I know now backasswards. Well the damn thing went to shooting 1/2 to 3/4 groups with a full case of 4831 and 190 Match Kings. 5 shot groups that is! By all that was written it should not have been able to hit a barn if fired from inside it. Oh by the way the 4831 is considered to be an overload now! The load was given to me by an old shooter that had been using it ever since he got some of the irst H4831 sold. He never had a problem and I did not either . I did back off a lil when I got my first manuals. That was almost 40 years ago. Rifle is still bedded wrong and still shooting less than 1 inch . ------------------ Carlyle Hebert

July 2, 2000, 08:06 PM	#9
Hueco Senior Member Join Date: December 7, 1999 Posts: 561	Alright, I was going to post this question seperately, but it fits in well here. Say you have a 30 calibre rifle, twist is 1 in 12" and it won't stabalise 220's. What if you up the velocity? Wouldn't the bullet be spinning faster after leaving the muzzle? Would that work? And is this the principle load-development works on? Hueco

July 2, 2000, 09:23 PM	#10
Southla1 Member In Memoriam Join Date: March 19, 2000 Location: Jeanerette, La. Near the Posts: 1,999	It may help some Hueco, but the really best way to do it is up the twist (or is it down ? ) Oh hell go to a 1-10 or 1-9 In all seriousness try this site if you have a chance it gives a lot of good info! I am going to ahve to sneak a printer cartridge on the boss (wife) one day and print the whole thing it is a great article, but the pictures will eat up an ink cartridge lol. http://www.povn.com/~4n6/index.htm ------------------ Carlyle Hebert

July 2, 2000, 09:34 PM	#11
Ruben Nasser Senior Member Join Date: March 29, 2000 Location: Asuncion, Paraguay Posts: 280	Hueco, yes, increasing the velocity will also increase spinning rate linearly, but in a given caliber you don't have much room to get the 20% increase in velocity needed to compensate from 1 in 10" to 1 in 12", that's why you are restricted from the beginning to a certain range of optimum bullet lenghts (and weight). As Southla1 said, sometimes you get different results in the real world (and nobody knows why...). Load development is a different thing, and is basically selecting components (one bullet, different powders/primers)and trying different combinations until you achieve the results in velocity, consistency, pressure, and accuracy that you desire. Past this you try different seatings depths (and MANY other thigs) to fine tune the load. Look in www.snipercountry.com , there are a couple articles on this.