I am going to re-barrel an action to 30-06. I have been calling around trying to get opinions on the twist rate that would be optimum, but so fare its split 50/50 on 1 in 10 or 1in 11. This 06 will get a steady diet of 180 and 200 graing bullets 90% of the time. However I might like to try the 165 and 220 on ocassion just for fun. I do have a 280 that takes care of the 160's and a 338-06 that can handel the 225's. What is the the best twist rate for 180's and 200's.

1 in 10

quote:

Originally posted by Jim White:
1 in 10

ditto

quote:

1 in 10

Make that 3 votes for the 1 in 10

1 in 10. I don't think the 1 in 11 will stabilize the longer heavier bullets.

would the 1 in 11 be better with the lighter pills, say 125 to 150?

quote:

Originally posted by Alex.Y:
would the 1 in 11 be better with the lighter pills, say 125 to 150?

My 30-338 is a 1 in 12 and handles 165gr bullets just great but the longer 190gr Speers won't stabilize. The slow twist seems to help with velocity. My 30-338 pushes 150gr Sierra HPBTs at 3547fps. Great for Antalope.

The 30-06 is a it's best with 165 and 180gr bullets which can EASILY be stabilized by a 1:12" twist rate

the 1:10" twist rate that is "traditional" for the 30-06 is a hangover from the 30-03 with it's 220gr roundnose projectiles.

there IS such a thing as "overstabilization"
but it's mostly only relevant to long range shooters (800-1000yd).
a 1:10" (or faster) twist rate can prevent some bullets from "tracking" as they fly to longer ranges and will "belly" through the target at 1000yds.

(remember that if you launch a bullet at a significant upwards angle and it's well stabilized the bullet will come back down at that same attitude with respect to the earth and will fall back through line of sight with a "nose up" aspect to the target

This is why match barrels for the 308Win are frequently made with 1:12" (or slower) twist rates, the slower twist rate allows the bullet to essetially "weathercock" and stay nose-on to it's direction of flight.

this problem becomes even more pronounced on "indirect fire" artillery projectiles... Anyone remember Gerald Bull?
(the "supergun" guy?) anyway he added spiral vanes to the ogive of 155mm Howitzer projectiles so that the air flowing over the nose of the projectile would maintain their stabilizing rotation to prevent precession as the projectile
transitioned from the "nose up" firing attitude to the "nose down" attitude as it arrived on target, this coupled with a
change in the weight distribution of the projectile kept the 155mm shells pointed in direction of flight and increased the range from a 155mm gun by several miles...

So if a 1:12" twist works for a 308Win with 190gr VLD match bullets it'll certainly work for similar and lighter bullets in the 30-06.

IOW, unless you are SERIOUS about using 200, 220gr or even 250gr projectiles in the 30-06 you don't need a 1:10" twist rate.

And if you actually NEED to use bullets heavier than 180gr
you probably need a 300magnum to launch them anyway.

So if it's a choice between 1:10" and 1:11" I say go with the 1:11", and seriously consider 1:12"

Personally if don't think I can get the job done with a 165gr bullet from my '06 I'll dig to the back of the gun safe and get out
my 338WinMag and use a 225gr bullet.

AllanD

I shoot .308 match rifles and use a 1-10 twist for bullets from 150-190 grains no problem. I currently have an Obermeyer 1-11 barrel on my Across the Course rifle and it does quite well with 175 and 190 grain Sierras. Either will work fine but 1-10 would be best.

Yes, but are you shooting 800 & 1000yds?

As the "overstabilization" is usually only an issue for "tracking" at very long range for 30cal projectiles.

and then not for all projectiles....

I remember one aquaintance complaining that one particular bullet (SMK?) was not tracking right out of his fast twist (I believe a 1:9") barrel but the 190 grain rebated boattail lapua match bullet didn't exibit the same charteristic.

His next barrel was a 1:12 and though it shot the (expensive) lapua's well it shot the SMK's better.

AllanD

Twist does affect accuracy.

To the extent that a bullet is not perfectly balanced, spin will cause the unbalanced bullet to wobble after it leaves the barrel. As rotation and imbalance increase, wobble increases (the word "wobble" is just my slang, it's actually much more complicated than that, but the bottom line is, the group size will increase).

This is true at any range and with any weight.

You can find the formula in either Vaughn's book or Mann's book.

Since modern jacketed bullets are generally well made and well balanced, you will not likely notice a difference in accuracy in a sporting rifle.

Benchrest shooters, on the other hand, pay attention to these things.

quote:

Originally posted by Alex.Y:
would the 1 in 11 be better with the lighter pills, say 125 to 150?

Story from General Hatcher: Once a particular batch of 1903 Springfields newly completed at the Armory proved to be noticeably more accurate than the typical Springfield product. The reason for this turned out to be that one of the rifling machines had "slipped a cog", and was rifling barrels with a 1/11" twist rather than the specified 1/10" twist. The machine was repaired so that it went back to making the "correct", less accurate, 1/10" twist!

This story did not specify which bullet weight was being used at that time, the original M1906 150-grain flatbase or the later "M1", 173 grain spitzer boattail.

I think you'd get better accuracy with a 1/11" twist if you limited your bullets to no more than 165 grains. But if you will "occasionally use" 220 grainers, make it a 1/10".