Rule of thumb for bullet weight and twist rate?

[JeepsAndGuns]

Wasnt sure of where to put this question so hopefully this is a good place to put it.
I am wondering what the rule of thumb is for bullet weights and barrel twist rates? All I know is that for a given caliber, a twist rate of XX is best for bullets of XX weight. What I dont know is what twist rates are good for what weights.
Is it fast twist rates good for heavy bullets, or light ones? And vice versa

Say you going to order a barrel for 6.5mm cal, and avalable twist rates are one turn in 8,9,10, and 12. Witch would be best for 140gr bullets?
Then say you have a 30cal barrel with a twist rate of one turn in 10, what would be the best weight bullet for this rate? Heavy or light?

Trying to learn as I go here.

[Son of the Gun]

J&G, to answer your question about fast/slow rifling for heavy/light bullets: if the twist is faster, it will generally perform better with heavier bullets and slower will perform better with lighter bullets.

For the 6.5mm question, either the 1:9 or 1:10 would work well with 140gr bullets, and the 1:8 would probably work better for 160's.

For the .30-cal with a 1:10 twist, anything from 175-200gr should do well in this rifle. 200's may be pushing it for stability (they may be better suited by a 1:9.5 or 1:9 twist), and anything under 175 may "overstabilize" due to the twist rate, but that range should work well for you.

For the general rule of thumb, knowing (for each caliber) which bullets are considered "heavy" and which are "light," as well as the "middle ground" for each caliber really helps.

[JeepsAndGuns]

Thanks for the reply, that really clears things up.
The two guns in question are a 30-06 with a 24in 1:10 twist barrel. I have been shooting some 168 gr bullets, but now I may step up to some heaver ones.
The 6.5mm is a large ring mauser I am rebarreling to 6.5X55, and I was wondering what twist rate would be best for the 140gr bullets. The selection of types and brands of 140gr 6.5mm bullets seems good. So I will use those. I am getting ready to buy a heavy target barrel and wasnt sure on the twist rate.

[Son of the Gun]

Well, for the .30'06, some of the earlier models, like the Springfield '03 for example, used 1:9.5" twist rates because the .30'03 cartridge was essentially a ".30-40 magnum" using the same 220gr RN bullet, just at a substantially higher velocity. Even when the 180gr M1 Ball was developed, the 1:9.5" twist was retained, though unnecessary for the lighter bullets. 168gr bullets will shoot well out of anything from 1:12" to 1:10" with .30'06 velocities. For your rifle, though, you may want to try finding some 175's and see how they shoot for you.

As for the 6.5x55 Swede, if memory serves, they used 1:8.5" twist in their M96, M38 and whatever else rifles came from Sweden. However, rifling that fast isn't entirely necessary for the 140gr 6.5mm bullet. Actually, it's more suited to long, heavy 160gr bullets. I would go with 1:9" twist, because that will still stabilize the long 140's.

[JeepsAndGuns]

The 30-06 is a 03 springfield. It was given to me by my grandfather. It has been sporterized and has a scope mounted. So I do not know witch model of 03 it is, or when it was made. All I know is it has the original barrel that has been turned down to a sporter contour. I measured the twist rate with a cleaning rod and a tight patch. It measured almost perfectly at 10in for one turn. I am working up a load with some 168gr SMK's and so far it has had some pretty decent groups. Even for the low 2.5 power scope. One I shoot up this box, I will get some heaver ones and see how they do.

I am pretty sure the twist rate on (at least) the M96 is 1:7.5, thats what my hornady book listed, as they used a M96 for testing, and I remember reading it on here too. I just started on a load for it, and picked up a box of hornady 140gr A-max bullets. And right there on the box it says twist rate 1:7.5. So I think those may be made for that twist rate. When I get my other one built, I will probably use the 140gr SMK's

[armyrat1970]

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Okay. But how does that apply here on this forum?

[JeepsAndGuns]

Wow, one year to the day. Has it really been that long since I posted this?


And I think I missed something. Amazon berries?

[AmmoSgt]

Okay.. common mistake.. it's not the weight of the bullet, but the lenght relative to the diameter... of course , normally longer bullets are heavier..

anyway here are the deails and equations to calculate the proper twist.. along with some comentary


http://www.frfrogspad.com/miscellb.htm#accurate scroll down the question #6

[Optimist]

Wow, one year to the day. Has it really been that long since I posted this?


And I think I missed something. Amazon berries?

:eek:Moderator pulled this, so it is no longer cluttering up the forum.:eek:

[effedyFrura]

Well after a month and a half on Renewed Life acai berry juice my vision has take a drastic turn for the better.

[gun_lover]

:eek:Moderator pulled this, so it is no longer cluttering up the forum.:eek:

Apparently it is tiime for another Moderator intervention...

[armyrat1970]

Apparently it is tiime for another Moderator intervention...

Yeah I agree but in one aspect I have interest. Again I agree with you Dan. This is not the right forum for this but I suffer from AMD. But this is not the right forum to post this about. But I'm glad he did and I ran across it before it was deleted. Sending him a PM.

[JeepsAndGuns]

Wow, twice that this thread has been brought back from the dead by totaly random off topic posts? What gives?

[Oldstuffer]

It's not really a "rate of twist related to weight", it's a "rate of twist related to length (which, per calibre, is related to weight)". It is also related to bullet velocity, which relates it to rotational RPM.

Here, a bit from the 'net:

One of the first persons to try to develop a formula for calculating the correct rate of twist for firearms, was George Greenhill, a mathematics lecturer at Emanuel College in Cambridge, England. His formula is based on the rule that the twist required in calibers equals 150 divided by the length of the bullet in calibers. This can be simplified to:

Twist = 150 X D2/L

Where:
D = bullet diameter in inches
L= bullet length in inches
150 = a constant

This formula had limitations, but worked well up to and in the vicinity of about 1,800 f.p.s. For higher velocities most ballistic experts suggest substituting 180 for 150 in the formula. The twist formulas used in the Load From a Disk program, featured at this web site, uses a modified Greenhill formula in which the "150" constant is replaced by a series of equations that allow corrections for muzzle velocity from 1,100 to 4,000 fps.

I think this is a fair explanation of it:
http://www.loadammo.com/Topics/July01.htm

[curioushooter]

Greenhill's formula

I second above. It's a bullet lenght to twist rate question, not weight, though weight and length are closely related if the same materials are used.

[Ordtech]

Why not ask the barrel manufacturer for their recommendation? They generally have a good idea what performs best in their barrels and sometimes have recommendation charts on their websites.