When you are making the decision on a barrel for you next rifle project I know that you would base the decision of what twist on the longest / heaviest bullet you plan to use. My question is if you can't over stabilize a bullet why would you nt just pick the fastest twist available in the barrel of your choice?

What are the drawbacks of using a twist much faster than required for a light bullet?

Will it cause an increase in pressure or a reduction in velocity or both?

Would the barrel foul quicker because of the speed of the bullet & the friction placed upon it by trying to twist it faster?

Finally would you expect to see more accuracy at longer distances or not as much distance?

When striving for absolute accuracy, the slowest twist rate, that will stabilize your bullets, is recommended. Faster twist rates will shoot well with the lighter bullets. They just won't shoot as well as the slower twists.

Interesting question.....

With varminting calibers one can easily overstabilize in that one can create so much centrifugal force as to actually blow up bullets in mid air and many of us have had that happen to them. The bullet never reach a target at 100 yrds.

I built a 6 X 45 on a 1-14" twist thinking I could increase velocity by reducing turns and as it turned out I was right.....but the gain was almost unmeasurable as the amount of energy needed to increase the RPMs is incredibly small so I actually lost the ability to drive heavier bullets instead of gaining measurable velocity.

To your point.....If one was building a .243 there would be nothing wrong with a twist of 1-9" instead of the known working standard of 1-10". If one was building a 7 mm he could choose a 1-8" as well as a 1-9" which is the most used without a problem. and so on.....

In many calibers we can get light jacketed "A-Max" style bullets which could disintegrate in mid air if turned too quickly and any bullet conceivably could "blow up" if turned at (for example) a twist of 1-3".... and while I've never thought about this I suppose there would be a point that we're putting so much energy into rotations that we'd have to reduce velocity to keep pressures in line. This don't really happen in smaller differences as 1-9" verses 1-10".

Simply stated we find that there's twists in each caliber that are totally adequate for todays hunting and varminting bullets that are totally adequate and that there is no point in turning them faster even though a bit faster doesn't hurt.

I look to my loading manual that states the twist used for the load being used and look at all the cartridges of that caliber and decide from there.

Here's a wierd one.....the .25-20 has a standard twist of 1-14" but if I was building one today I'd use a 1-10" without reservation and wouldn't reduce loads because of it. Nothing wrong here! I wouldn't gain anything however except that that barrel could then also be used for a 250-3000 some day and a 1-14" wouldn't be a good choice for the longer bullets in the .250 Sav.

Possibly the best answer is simply that there's no point in turning a bullet any faster than necessary to stabilize the longest bullet of that caliber you intend to use and still not "blow up" the lightest jacketed one.

There are historically twists of each caliber that have proven useful and we tend to stick with what has proven to work......if that's a good enough reason!

Thanks for the responses guys.

as well as pressure changes...

the SOLE reaon that every gun isn't in the fastest twist possible is pressure...

it is acceptable to use the greenhill formula and go 1 or 2 twists faster, this hurts nothing

you should have seen the faces at (famous benchrestbarrelmakers) when asked what happens when you over twist a barrel 50% faster than required..

jeffe

is a 1:8 twist 50% faster than a 1:16 twist?

quote:

Originally posted by tin can:
is a 1:8 twist 50% faster than a 1:16 twist?

a 1-8" twist is 100% faster than a 1-16".....

but a 1-16" twist is only 50% of a 1-8" twist.
depends on how you say it!

whath vapo said....

$100 is 100% more than $50

for $50 is 50% of $100....

heh

quote:

a 1-8" twist is 100% faster than a 1-16".....

but a 1-16" twist is only 50% of a 1-8" twist.
depends on how you say it!

so 1:12 is 50% faster than 1:16.

methinks...

quote:

Originally posted by jeffeosso:
as well as pressure changes...

the SOLE reaon that every gun isn't in the fastest twist possible is pressure...

it is acceptable to use the greenhill formula and go 1 or 2 twists faster, this hurts nothing

you should have seen the faces at (famous benchrestbarrelmakers) when asked what happens when you over twist a barrel 50% faster than required..

jeffe

So I can expect to see a rise in pressure without gaining any velocity?

quote:

Originally posted by tin can:

quote:

a 1-8" twist is 100% faster than a 1-16".....

but a 1-16" twist is only 50% of a 1-8" twist.
depends on how you say it!

so 1:12 is 50% faster than 1:16.

methinks...

quote:

So I can expect to see a rise in pressure without gaining any velocity?

Did you ever see load data that had a chart for twist rate?....loading data is for the cartridge primarily and the (normal) twist. Twist rate isn't relevant!

Yes.....a faster twist will generate higher pressures but it will still be extremely slight as the amount of energy it takes to rotate the bullet is small......if you always start low and work up it's irrelevant.

There is probably more pressure variation from cartridge to cartridge than there is between different rates of twists...within reason of course.

Actually...
i built 2 and bought a 3rd, 358 winchester to test this very idea.

1x16 (savage 99) 1x12 and 1x10 douglas barrels.

across the board the 1x10 produced higher repressures, without a doubt.

in fact, TWIST is specified in both SAAMI and CIP for rounds, as it is KNOWN to change pressure.

for example, you can not buy a 470 NE with faster than 1x18 twist, and that is ONLY if it's an american rifle... nominal is 20 and 22, saami and cip (but I forget which is which)

BTDTGTTS

If you took a 223 and built total max safe loads in a 1x12 and stuck them in a 1x7 you will, without a doubt, have a pressure excursion above saami.


jeffe

Well don’t keep us in suspense...how much more pressure did the faster twist create, and what device was used for the testing?

When going from a 1:14 to 1:10 twist, the pressure difference will be insignificant and can be ignored, as proven by lab testing at Somochem.

quote:

Originally posted by 500grains:
When going from a 1:14 to 1:10 twist, the pressure difference will be insignificant and can be ignored, as proven by lab testing at Somochem.

But Jeffe was never one to be bothered by facts.

quote:

Originally posted by 500grains:
When going from a 1:14 to 1:10 twist, the pressure difference will be insignificant and can be ignored, as proven by lab testing at Somochem.

This is consistant with my experience however unscientific my experience is!

quote:

Originally posted by 500grains:
When going from a 1:14 to 1:10 twist, the pressure difference will be insignificant and can be ignored, as proven by lab testing at Somochem.

Dan,
please post this data, which you have frequently referred to, or a link to such. This is not a truth jihad, rather a request for your oft quoted source.

And jeff, please post your test data.

quote:

Originally posted by jeffeosso:

quote:

Originally posted by 500grains:
When going from a 1:14 to 1:10 twist, the pressure difference will be insignificant and can be ignored, as proven by lab testing at Somochem.

Dan,
please post this data, which you have frequently referred to, or a link to such. This is not a truth jihad, rather a request for your oft quoted source.

Well? I have performed several web searches and can not find such data.

Please post the link, publication data, contact, heck, even PM the stuff.


perhaps you meant somchem? as there is no such company as "somochem" that makes reloading powders

jeffe

I have, however, searched this site

(somchem is owned by denel)
http://www.dlswc.co.za/

and could find no link to ANYTHING related to twist.

So I emailed their small arms contact for the information

jeffe

So,
Dan, if your PMs were on, I would have sent you this directly, rather than doing this in public. Somchem denies performing such a test.

email me your email address and I'll forward this email to you, Dan.

Here's the question from me to Somchem

quote:

Greetings,

I heard that your company performed a test on varying twist rates and that effect on pressure.

If so, could you please forward me a copy of this document, as I am greatly interested in the general effects of increased twist and pressure in small arms barrels.

if not, please let me know

jeff smith

Answer
from Manie Johannes, Somchem/DLS-WC, Ballistic Proof Range

quote:

Jeffe

Sorry we did not do any test on the verification of the twist and the pressure accompanies it.

So we don’t have any documents regarding these test.

Manie Johannes

DLS-WC
Ballistic Proof range

quote:

Originally posted by jeffeosso:
as well as pressure changes...

the SOLE reaon that every gun isn't in the fastest twist possible is pressure...

it is acceptable to use the greenhill formula and go 1 or 2 twists faster, this hurts nothing

you should have seen the faces at (famous benchrestbarrelmakers) when asked what happens when you over twist a barrel 50% faster than required..

jeffe

This is absolute crap. The sole reason I order 14 twist barrels for BR rifles in 6ppc and 17 twist barrels in 30BR has zero to do with pressure. It has everything to do with the slowest twist possible in order to attain the best accuracy available from the bullets to be used. If I want to shoot heavy bullets in a 6mm, I use and 8 twist. A 14 wont stabilize the heavy bullets. What in the hell does any of this have to do with pressure? Before you spout off with your narrow minded reasoning, you may wan't to give things a little thought.

The person at Somchem who originally mentioned the non event of pressure / twist rate relationship to me was Johan Loubser. He left Somchem more than ten years ago and that is likely the reason why Manie Johannes has no knowledge of such tests. I do not know if Johan did formal testing along twist / pressure lines or whether he investigated the premise and found so little merit that it was not formally pursued. I will try to find out. Jeffe, you should know this as I posted this in between two of your posts.


Pointblank makes the point clearly. Twist and bullet length determine how a bullet behaves over the intended trajectory. If the cartridge remains as a constant, the best results will be obtained with three different twist rates for 300m bench, one mile bench and for hunting to normal distances. Unless you vary the bullet length and shape to accommodate the three disciplines with one twist rate........

The bottom line is that twist rate is chosen to obtain a particular external and terminal ballistics result. Because we are intelligent people, we then measure pressure and speed as we work up to the end product.

Anyone who builds a 338 Lapua Magnum on a 1:7" twist in order to use our 295gr SP bullet for shooting one mile, deserves all he gets if he allows another reloader to fire his 200gr, max velocity hunting load in the same rifle.

Also note that there is no way that any factory ammunition will cause a problem in any rifle as a result of twist being too tight. Factories know better than to load to levels where an out of (CIP / SAAMI) spec rifle could be a liability. That is why we hand load rather than use factory fodder:- to optimise the load to the rifle and the intended use.

Johan is now at Ramshot/AA and is one of the nicest folks I've dealt with when it comes to ballistic info/data.

Don't know anything about the pressure differential, but I do know that my 6mmPPC with a 1:14 twist Krieger will shoot .25in groups at 200yds with 70gr Sierra BTHP match bullets, Vihtavuori powder and federal match primers. It will keyhole at 50yds anything heavier that 90grs.

I wonder if Jeff is satisfied now.

quote:

Originally posted by pointblank:
If I want to shoot heavy bullets in a 6mm, I use and 8 twist. A 14 wont stabilize the heavy bullets. What in the hell does any of this have to do with pressure? Before you spout off with your narrow minded reasoning, you may wan't to give things a little thought.

Yes, sir... You know, I just may have given this a bit of thought...
your remarks are entirely in regards to external ballasics... how the bullet performs once out of the barrel.

this discussion is on INTERNAL ballastics...

how twist increases pressure

Now, what IS real, even dan admits that there is SOME pressure change, is that you go with a faster twist, then you get higher pressure.

the quetion is HOW MUCH, not IF.

so, yes, please, let's certainly not be narrow minded... so you could try this...

take your fastest, bestest load in the fast twist rifle, and WITHOUT CHANGING A THING shoot it in your slow twist rifle... and chronograph it and look at the primer...

hmm, less pressure..

DO NOT DO THE INVERSE... you risk injurty and damage to your gun

quote:

Originally posted by Gerard:
The person at Somchem who originally /b]mentioned [/b]the non event of pressure / twist rate relationship to me was Johan Loubser.

I do not know if Johan did formal testing along twist / pressure lines or whether he investigated the premise and found so little merit that it was not formally pursued. I will try to find out.

Gerard, without I doubt I recall your passing statement on this. However, then, as in know, SOMCHEM never made the statement that the twist could be disregarded, as Dan states

quote:

Originally posted by Gerard:

[URL=https://forums.accuratereloading.com/eve/forums/a/tpc/f/4711043/m/325104665?r=481104085#481104085]

Pointblank makes the point clearly. Twist and bullet length determine how a bullet behaves over the intended trajectory.

not exactly. He frames the correct and MINIMUM twists required to get a bullet stablized.

quote:

Originally posted by Gerard:
The bottom line is that twist rate is chosen to obtain a particular external ...
Also note that there is no way that any factory ammunition will cause a problem in any rifle as a result of twist being too tight.

I disagree, in fact, any high presure load (300 weatherby or 458lott) in a too fast twist barrel WILL have higher pressure than a standard twist barrel.

quote:

Originally posted by Gerard:
Factories know better than to load to levels where an out of (CIP / SAAMI) spec rifle could be a liability.

which is why saam/cip spec a twist

quote:

Originally posted by 500grains:
I wonder if Jeff is satisfied now.

somchem denies knowledge of said report.
email to ramshot asking the same



I am totally satisfied that this reference to somchem is not accurate nor an offical position


jeffe

Sanity question...

if the reloading manuals challenge one to develope new loads just for using another makers bullet, how can one even begin to accept two greatly different twists are the same performance?

For those of you that don't think a really fast twist can raise pressure, how come, besides ruining your accuracy, it NOT recommended to shoot your rifle with a coat of oil in the bore?

Joe

I always shoot my rifles with a coat of oil in the bore. Just not a thick coat.
First shot is for lube and then the graphite in the powder takes over.

quote:

Originally posted by Pegleg:
I always shoot my rifles with a coat of oil in the bore. Just not a thick coat.
First shot is for lube and then the graphite in the powder takes over.

Okay, why not a thick coat...hmmmmmmmm?

quote:

somchem denies knowledge of said report.
email to ramshot asking the same

I am totally satisfied that this reference to somchem is not accurate nor an offical position

Jeff,

Surely it would be easy to test presure differencials at a proofhouse?
Curious to see some test data.

Warrior

quote:

Originally posted by Warrior:

quote:

somchem denies knowledge of said report.
email to ramshot asking the same

I am totally satisfied that this reference to somchem is not accurate nor an offical position

Jeff,

Surely it would be easy to test presure differencials at a proofhouse?
Curious to see some test data.

Warrior

Hi Chris,

Do you agree that twist rate is basically a non-issue with regard to pressure?

quote:

Originally posted by Warrior:

quote:

somchem denies knowledge of said report.
email to ramshot asking the same

I am totally satisfied that this reference to somchem is not accurate nor an offical position

Jeff,

Surely it would be easy to test presure differencials at a proofhouse?
Curious to see some test data.

Warrior

Warrior,
it ceratinly would be interesting, no? Which is why I emailed SOMCHEM that denied all knowledge, and then emailed (and called - got VM) Ramshot.

So, let's be clear...

the statement was SOMOCHEM{sic} says it makes no difference.

I chanllenged that statement, and accepted that Dan meant Somchem.

I emailed Somchem, they deny all knowledge of said position

Gerard reminds us that he heard this from Johan (who, by all regards, is a fine chap) rather than a Somchem position.


QED (actually, in this case, it is NOT proven) Somchem never made this statement, rather PERHAPS Johan did, as a person.

Completely different statements, one a personal comment by Johan the other an offical lab position.

WHICH IS WHY I ASKED FOR THE FACTS in the first place.

jeffe

quote:

Originally posted by 500grains:
Hi Chris,

Do you agree that twist rate is basically a non-issue with regard to pressure?

Dan,
No one really believes this, sorry

Pretty much the end of the somchem discussion, as false

Now we are working on what pressure labs have to say on the matter.

quote:

Originally posted by 500grains:
When going from a 1:14 to 1:10 twist, the pressure difference will be insignificant and can be ignored, as proven by lab testing at Somochem.

quote:

Originally posted by jeffeosso:
from Manie Johannes, Somchem/DLS-WC, Ballistic Proof Range

quote:

Jeffe

Sorry we did not do any test on the verification of the twist and the pressure accompanies it.

So we don’t have any documents regarding these test.

Manie Johannes

DLS-WC
Ballistic Proof range