Gunsmithing Twist rate for 7.62
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Re: Twist rate for 7.62
I like something along the 1-11/11.25 twist. I would consider the 1-10" if I were going with someting like a 20" barrel.
I like something along the 1-11/11.25 twist. I would consider the 1-10" if I were going with someting like a 20" barrel.
Re: Twist rate for 7.62
1 in 10 is a great twist rate. Perfect with 175 SMK's but leaves the options open to heavier higher BC bullets and subsonics.
Wade.
1 in 10 is a great twist rate. Perfect with 175 SMK's but leaves the options open to heavier higher BC bullets and subsonics.
Wade.
Re: Twist rate for 7.62
Barrel length has nothing to with twist. Velocity and bullet lenght(weight) is what determines twist. With you using 175gr bullets, any twist from 10-12 will work. There is not enough difference in them twist rates to worry about.
Barrel length has nothing to with twist. Velocity and bullet lenght(weight) is what determines twist. With you using 175gr bullets, any twist from 10-12 will work. There is not enough difference in them twist rates to worry about.
Re: Twist rate for 7.62
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: excaliber</div><div class="ubbcode-body">Barrel length has nothing to with twist. Velocity and bullet lenght(weight) is what determines twist. With you using 175gr bullets, any twist from 10-12 will work. There is not enough difference in them twist rates to worry about. </div></div>
I think his point is that shorter barrels tend to yield less velocity.
I'm partial to 1-10, as it'll easily handle any 30 cal bullet the 308 case can launch.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: excaliber</div><div class="ubbcode-body">Barrel length has nothing to with twist. Velocity and bullet lenght(weight) is what determines twist. With you using 175gr bullets, any twist from 10-12 will work. There is not enough difference in them twist rates to worry about. </div></div>
I think his point is that shorter barrels tend to yield less velocity.
I'm partial to 1-10, as it'll easily handle any 30 cal bullet the 308 case can launch.
Re: Twist rate for 7.62
If 1,000 yards is the goal, go with a 10. 175s will still perform but the heavies will get you to 1k with a few less clicks on your scope.
If 1,000 yards is the goal, go with a 10. 175s will still perform but the heavies will get you to 1k with a few less clicks on your scope.
Re: Twist rate for 7.62
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body">I shoot 180VLDs from a 12 twist at 1000, in the winter.</div></div>
Why in the winter? What is the advantage? How does it preform?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body">I shoot 180VLDs from a 12 twist at 1000, in the winter.</div></div>
Why in the winter? What is the advantage? How does it preform?
Re: Twist rate for 7.62
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Paramil</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body">I shoot 180VLDs from a 12 twist at 1000, in the winter.</div></div>
Why in the winter? What is the advantage? How does it preform? </div></div>
Thicker air = More twist required
Thus, lower altitude and colder temps yields worst case scenario for proper bullet stabilization.
A barrel that can stabilize a given bullet at 1000' above sea level in the summer at 90° might not stabilze that same bullet at lower altitudes or in cooler weather. A 1:12 308 launching the 208 amax is a good example. These tend to do great in the summer, and often don't work in the winter.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Paramil</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body">I shoot 180VLDs from a 12 twist at 1000, in the winter.</div></div>
Why in the winter? What is the advantage? How does it preform? </div></div>
Thicker air = More twist required
Thus, lower altitude and colder temps yields worst case scenario for proper bullet stabilization.
A barrel that can stabilize a given bullet at 1000' above sea level in the summer at 90° might not stabilze that same bullet at lower altitudes or in cooler weather. A 1:12 308 launching the 208 amax is a good example. These tend to do great in the summer, and often don't work in the winter.
Re: Twist rate for 7.62
Barrel length has everything to do with twist. If you are running a marginal twist rate for a 175gr bullet like a 1/12 then you don't want a 20" barrel. You lose velocity and when you lose velocity you lose bullet rpm and thus stability. For a 25" barrel a 1/12" twist will work just fine.
Barrel length has everything to do with twist. If you are running a marginal twist rate for a 175gr bullet like a 1/12 then you don't want a 20" barrel. You lose velocity and when you lose velocity you lose bullet rpm and thus stability. For a 25" barrel a 1/12" twist will work just fine.
Re: Twist rate for 7.62
i would not consider the 1-12 marginal for the 175. generally speaking you want the slowest twist that will stabilize your intended bullet under all conditions. a slower twist will yield more velocity as well. in the early days of benchrest the .308 168MK was a very popular combonation and they ran 1-14 twist barrels. a 1-13 is sufficient to stabilize the 175MK under MOST conditions. if you are ordering a blank, and are willing to wait, a 1-11 would probably be the most versatile if you thought you might want to try the 208 at some point. otherwise the standard 1-12 will do all the .308 was intended to do.
chuck
i would not consider the 1-12 marginal for the 175. generally speaking you want the slowest twist that will stabilize your intended bullet under all conditions. a slower twist will yield more velocity as well. in the early days of benchrest the .308 168MK was a very popular combonation and they ran 1-14 twist barrels. a 1-13 is sufficient to stabilize the 175MK under MOST conditions. if you are ordering a blank, and are willing to wait, a 1-11 would probably be the most versatile if you thought you might want to try the 208 at some point. otherwise the standard 1-12 will do all the .308 was intended to do.
chuck
Re: Twist rate for 7.62
I run an 1/11.25" twist on a 24" Bartlien and it shoots 155's-175's with incredible accuracy out to 1k. If you go any heavier you may want to consider 1/10" twist.
I run an 1/11.25" twist on a 24" Bartlien and it shoots 155's-175's with incredible accuracy out to 1k. If you go any heavier you may want to consider 1/10" twist.
Re: Twist rate for 7.62
1:10 works. Given a choice an overstabilized bullet is more desirable than going the other way.
As for air density:
Look up "magnus effect".
The USMC Reserve team used to shoot a match in Bailey, CO shortly before Camp Perry. Bailey is almost 9000ft. Perry is a few hundred. Don't recall anyone ever talking about rebarreling their service rifles to adapt to air density. Same guns, same load. Guns worked just fine.
Loads sometimes get a little fussy on hot days but that has more to do with charge weights and pressure than anything. When you steam 80g vld's at ludicrous speed primers get fussy.
I dunno . . .
C.
1:10 works. Given a choice an overstabilized bullet is more desirable than going the other way.
As for air density:
Look up "magnus effect".
The USMC Reserve team used to shoot a match in Bailey, CO shortly before Camp Perry. Bailey is almost 9000ft. Perry is a few hundred. Don't recall anyone ever talking about rebarreling their service rifles to adapt to air density. Same guns, same load. Guns worked just fine.
Loads sometimes get a little fussy on hot days but that has more to do with charge weights and pressure than anything. When you steam 80g vld's at ludicrous speed primers get fussy.
I dunno . . .
C.
Re: Twist rate for 7.62
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: excaliber</div><div class="ubbcode-body">Barrel length has nothing to with twist. Velocity and bullet lenght(weight) is what determines twist. With you using 175gr bullets, any twist from 10-12 will work. There is not enough difference in them twist rates to worry about. </div></div> please add-in the length of the bullet to the mix too gene said a 3 way cut pie for the twist -bullet -barrel-temp [i looked up some old notes of his ]
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: excaliber</div><div class="ubbcode-body">Barrel length has nothing to with twist. Velocity and bullet lenght(weight) is what determines twist. With you using 175gr bullets, any twist from 10-12 will work. There is not enough difference in them twist rates to worry about. </div></div> please add-in the length of the bullet to the mix too gene said a 3 way cut pie for the twist -bullet -barrel-temp [i looked up some old notes of his ]
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