Which twist rate?

[tlfeathers]

I am planning a 30-06 build in which I want to use either 190, 200 or 208 grain bullets. I read Salazar's article on it in which he recommends a 1:11 twist rate for up to 210 grain bullets. Then in the section on chambering he writes, "If your preference is for heavier bullets like the 210 gr. and 215 gr. models now offered by Berger and Sierra, then I would suggest asking PTG for 0.070" longer freebore. That will still allow you to use medium weight bullets as well as the heavier ones. At this point, you might as well get a 1:10" twist barrel just for a slight margin of safety with respect to bullet stability in cold temperatures. I think once you go past the 200 gr. bullets, you're out of the "normal zone" with the .30-06 and it becomes a specialized chambering as opposed to an "all-around" shooter which is the .30-06's great strength." This left me a bit confused. I do not plan on going over a 210 gr bullet so for a 190 -210 weight range is 1:11 the best twist rate?

 

[XTR]

Re: Which twist rate?

get the 1:10

 

[stockdoc]

Re: Which twist rate?

Yep 1-10 will be about right

 

[seanh]

Re: Which twist rate?

1:10 for anything over 180grn

 

[3-0-hate]

Re: Which twist rate?

On the flip side and a bit of a reverse of the OP's question, say he goes with the 1-10" twist and then decides he wants to shoot a light bullet for whatever reason like a 150gr or similar, would it "over-stabilize" a shorter bullet like that?

I ask because I have been considering a fast twist tube for a .308 but dont want to limit myself to the heavier pills only.

 

[6Dasher]

Re: Which twist rate?

No, won't hurt. But if you don't need a faster twist, don't get one. 1:10 is meant for 220gr and up. If you're just shooting up to 180gr then you might consider 1:12 instead. 1:10 is pretty fast.

 

[JB02]

Re: Which twist rate?

No downside for getting a faster twist. Get the 1/10.

 

[TGagnon]

Re: Which twist rate?

I built a 300winmag a few years back that is an 11 twist. I have to say though that now that I have shot it I will never buy anything but 10 twist 30 call barrels except for 308's and I doubt I will be making any more of those.

 

[Graham]

Re: Which twist rate?

10-twist for a 30-06.

 

[tlfeathers]

Re: Which twist rate?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TGagnon</div><div class="ubbcode-body">I built a 300winmag a few years back that is an 11 twist. I have to say though that now that I have shot it I will never buy anything but 10 twist 30 call barrels except for 308's and I doubt I will be making any more of those. </div></div>

What was it about the performance of 1:11 that causes you to prefer the 1:10? It seems apparent from the unanimous emphatic replies that 1:10 is clearly the better performer, I'm just wondering what's the difference? Thank you everyone for your replies.

 

[Boogaloo]

Re: Which twist rate?

Tagged for info on ^^ that question.

 

[tlfeathers]

Re: Which twist rate?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: tlf1</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TGagnon</div><div class="ubbcode-body">I built a 300winmag a few years back that is an 11 twist. I have to say though that now that I have shot it I will never buy anything but 10 twist 30 call barrels except for 308's and I doubt I will be making any more of those. </div></div>

What was it about the performance of 1:11 that causes you to prefer the 1:10? It seems apparent from the unanimous emphatic replies that 1:10 is clearly the better performer, I'm just wondering what's the difference? Thank you everyone for your replies.</div></div>

Can anyone weigh in on this last question?

 

[MontanaMarine]

Re: Which twist rate?

1/10 opens a lot of doors without closing any. Heavies, subsonic, cold weather, short bbl, low vel.....

Whoever came up with 1/12 needs a good kick in the nuts.

 

[XTR]

Re: Which twist rate?

The trend in bullets today is higher BCs and longer heavier bullets bullets. It's not just the weight that makes the heavies less stable in lower twists, the length is even more of a factor. Longer bullets need more spin.

The rotation stabilizes the bullet. For a given bullet it becomes stable at a certain RPM, so shooting a long bullet at high velocities from a slower twist barrel will stabilize it for a while, until it slows down, as it slows so does the RPM so at 600 or 800 yards it will start to yaw. {RPM=(12/twist rate)*velocity ft/sec)}

The current crop of high BC 30 cal bullets wants a 1:11 or faster, the 185 Hybrid needs a 1:11, the 185 Jugg (old LRBT) will stabilize at 308 velocities to 1000 yards with a 1:12, at least it will pushed at the speeds you can get from a 30" barrel, not sure about shorter ones. I know some Palma guys who have used them with good accuracy from a 1:12. If you want to shoot the heavies in an -06 then get the 1:10. I'll bet you that if someone makes a 192 next month it will be longer with a higher BC than what's out there and will probably need a 1:10.

The downside to a 1:10 is that you do get a little more spin drift than from a slower twist, in my F-TR rifle it's 1/2 to 3/4 of an MOA from my 100 yard zero to my 1000 yard no wind zero. ("No wind" at 1000 yards is really hard to actually achieve)

I haven't built an -06 or looked at the mag length vs bullet length equation but it's likely that if you throat your rifle for the heavies and you try to load light bullets you're going to be jumping them too far to get primo accuracy anyway so don't sweat them.

 

[tlfeathers]

Re: Which twist rate?

XTR Thank you for the explanation! You raise another question for me. I do not plan on shooting any light bullets out of this rifle. It will be strictly 190-210 gr. So, how do I need to throat this rifle?

 

[XTR]

Re: Which twist rate?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: tlf1</div><div class="ubbcode-body">XTR Thank you for the explanation! You raise another question for me. I do not plan on shooting any light bullets out of this rifle. It will be strictly 190-210 gr. So, how do I need to throat this rifle? </div></div>

I have never played with an -06 so I don't know the limitations of the mag or magwell.

Typically with short action rifles we are always limited in how far out we can seat the long heavy bullets and still get into the mag, so the throat for a rifle that gets mag loaded will ideally have the bullet close to but not in the lands at max mag length. In your case you need to find out how long you can seat the bullets, then talk it over with your gunsmith and see what reamers he may have available, if you can't get a setup you like then call Dave Kiff at PT&G and tell him what you want to load and how long and he'll make a reamer that will do the job for you.

 

[tlfeathers]

Re: Which twist rate?

XTR Thank you!