Bullet length and twist rate?

[Big_Rig_416]

So i bought a remmy 700 in 308 with a 1 in 12 twist and 26 inch barrel, and i want to get serious about reloading for it. Ive heard the length of the bullet and the twist rate must be matched to get the most stability out of the round once it is fired due to the gyroscopic forces yadda yadda yadda... someone please explain what all of this means!

How do i find what length bullet to use? What weight should i use? Ill be shooting paper and steel, so no hunting.

Thanks guys!

 

[Paladin2147]

Re: Bullet length and twist rate?

Enjoy

http://kwk.us/twist.html

or

Just shoot "normal" 30 cal bullets from 110 to about 200 grains and you'll be fine.

 

[gstaylorg]

Re: Bullet length and twist rate?

Basically, the longer a projectile is, the faster it must spin to be stable. It's actually the bearing surface of the projectile, but length is generally proportional. You will often see bullet "weights" recommended for use with different twist rates. Although not technically correct, longer bullets are generally heavier, so this will usually work. So, longer (or heavier) bullets generally require a faster twist rate. Your 12-twist barrel should be fine for most bullets through the 168 gr range, maybe up to 175s, depending on the projectile and your muzzle velocity. Below is a link that explains some of the factors that go into this topic in a reasonably simple manner (go to "Twist Rate" through "Twist Rate and Bullet Stability".

http://en.wikipedia.org/wiki/Rifling

Also, JBM ballistics has an online twist rate calculator if you know accurately the dimensions of a specific bullet you're interested in:

http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi

 

[Big_Rig_416]

Re: Bullet length and twist rate?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: gstaylorg</div><div class="ubbcode-body">Basically, the longer a projectile is, the faster it must spin to be stable. It's actually the bearing surface of the projectile, but length is generally proportional. You will often see bullet "weights" recommended for use with different twist rates. Although not technically correct, longer bullets are generally heavier, so this will usually work. So, longer (or heavier) bullets generally require a faster twist rate. Your 12-twist barrel should be fine for most bullets through the 168 gr range, maybe up to 175s, depending on the projectile and your muzzle velocity. Below is a link that explains some of the factors that go into this topic in a reasonably simple manner (go to "Twist Rate" through "Twist Rate and Bullet Stability".

http://en.wikipedia.org/wiki/Rifling

Also, JBM ballistics has an online twist rate calculator if you know accurately the dimensions of a specific bullet you're interested in:

http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi </div></div>

Thanks! This helps a bunch!

 

[flashhole]

Re: Bullet length and twist rate?

Your 1:12 twist rate is actually considered a slow twist for a 30 cal. You may have accuracy/stability problems with bullets 180 grains and up. Something in the 165 grain weight class should work very nicely.