hi
greenhill formula indicate the rifling twist of 1/14 inches needed to stabilise a bullet with 1,5 inch length in 375 caliber, i wonder why all 375 rifles have 1/12 rifling twist? no bullet in 375 is longer than 1,5 inches in my collection of 300 grain bullets!!?
regards
yes

quote:

i wonder why all 375 rifles have 1/12 rifling twist?

Because the designers knew then that more than marginal stability for stable flight in air is needed. For half way decent straight line transition from flight to tissue, a much higher stability factor is needed. Stable flight requires an s/f of more than 1.1. General hunting with expanding bullets is good with a s/f around 1.5 and solids need upwards of 2. With solids, more is better.

Hi Gerard
Thanks for your reply. do you know if it is true that brno 602 and cz550 magnum have 1/14 twist rate in 375 H&H? or it is just a myth? if so i may keep using lighter solids like 270 gr bullets or less.
regards
yes

The only way to be sure about the twist rate of a barrel is to measure it yourself, or to watch it being measured. About half the rifles I have measured are not what they are supposed to be. If I were sold a 1:14" 375H&H, I would give it back as it is out of spec. I am unwilling to believe that any manufacturer of hunting rifles does not know that slower twist leads to problems and that faster twist hurts nothing.

As an extreme example - I once ordered 25 7mm barrels from a manufacturer for a series of 7x57 rifles I wanted to build. The first one I completed would not shoot accurately and, after almost a week of messing around with bedding, fore end pressure, scopes and different bullets, I measured the twist. It was 1:10.5". I measured the rest of them and the batch varied from 1:7.5" to 1:11". I sent 13 barrels back that were useless as 7x57 barrels.

Most of the time a small discrepancy does not matter but, when a barrel becomes more than an inch off the spec, especially on the slow side, I lose interest.

Hammer forged barrels are usually much closer to spec on twist than cut or button barrels. Most BRNO rifles I have measured were pretty close on twist spec. I have not measured a CZ550 in 375H&H that I can recall.

/

What could the problem possibly be, if it yields and SF value of 1.5 or more?
Air stability calls for a value of just more than 1.

Warrior

quote:

I measured the rest of them and the batch varied from 1:7.5" to 1:11". I sent 13 barrels back that were useless as 7x57 barrels.

Geeeez !!!! Who was the manufacturer or were they from different makers?

Fastest twist = 1 in 7.5"
Slowest twist = 1 in 11"
Variance = 3.5"
% variance = 3.5/7.5 = 47%

We should lobby that a manufacturer like this should go out of business.
Must be a bunch of kokolollies.

Warrior

Hi
thanks Gerard and Alf for your replies.
my own experience with rifle twist is . sharper twist better penetration, i own several rifles, 6,5x55, 3996, 8x57 and 375, the 6.5x55 will win every time when it comes to penetration in papper both wet and dry. according to grihill the twist of 1/15 will be enough for a bullet of 1,3 inch length and my hornady dgs bullets are 1,3 inch long, i beleive i have a good margin with them, anyway there are plent of big games downed by both 9,3x62 and 375 with such a twist as 1/14.
regards
yes

yes,
Are you sure your rifle is 14? I just measured two 375H&H rifles, a CZ550 purchased three years ago and an old BRNO that was bought used more than 12 years ago. Both are 1:12". Do measure your rifle yourself and be sure.

hi Gerard
well i have not any measuring device and mesuring with cleaning rode has never given me an accurate answere . i've got from 1/10 to 1/18!!! twists it depend how hard i draw the cleaning rode my rifle is a brno zkk 602 built in 1985. it seems the rifling is quite sharp visualy. i hope it had a 1/12 inch twist ,
regards
yes

If your rifle is a BRNO from the mid eighties I will bet on it that it is 1:12". We are getting a shipment ready to go to Finland and there will be a quantity of twist checkers with it. Get one from the guys below and measure. It is a universal tool that fits a wide variety of calibers. We give them away and it will only maybe cost you the postage.

Eraliike Riistamaa Oy,
http://www.riistamaa.fi
Tel. Espoo +358 9 4110 1290
Tel. Kouvola +358 5 375 0288

quote:

Originally posted by ALF:
Holland and Holland had their barrels cut with a 1:14 twist.
Original Mauser built 375's had 1:14 inch barrels
My 375 Brno's all have 1: 14 inch twist barrels

my 375's all shot very very accurately with 300 gr and 350 gr bullets, I have had good success with 380 gr bullets and even the 400 gr Frontiers ( that are actually quite short for weight, because it's just a blob of lead) will go under 1/2 inch

Alf,

Very interesting, and surely not commonly known ... not even by Gerard who claims a 1-in-14" twist is out of spec and thus no good.
It would be interesting to see the SF values of some of these bullets mentioned above in the various weight classes - even if we could just look at a few 300 gr bullets being the classical weight for the .375 H&H.

Warrior

thanks gerard i wish i could speak Finnish nice language but not easy to understand for me
regards
yes

Alf,

quote:

Holland and Holland had their barrels cut with a 1:14 twist.
Original Mauser built 375's had 1:14 inch barrels
My 375 Brno's all have 1: 14 inch twist barrels

Would you mind checking on this information? I have it that only very old Browning 375s were 1:14". There is no record of BRNO or H&H building anything other than CIP spec 1:12" If you are sure about this, I can ad it to the twist by manufacturer info I am assembling.

Chris Bek,
It is not me who "claims a 1:14" twist is out of spec". It is CIP. You know, the institution whose guidelines you claim are cast in stone and must never, ever, under no circumstances, be deviated from.

yes,
We correspond with them in English and there is no problem.

Alf,
As a matter of interest, Corlane will also have twist checkers. Contact them for some.

Hi Gerard
Where can I buy GS bullets in scandinavia? I mean do you have a general agent in Sweden or one of scandinavian countries?.
regards
yes

Gerard the Guru Supreme,

The issue here is you bogus theory that a Solid must have a SF value in excess of 2.5 - not even 2.44 will do according to your bogus theory. SF calculations will show that 300 gr bullets will be more than stabilized in a 1-in 14" twist in a 375 H&H.

Proof of bogus theory:

9,3/270 GS-FN bullet loaded to a MV of 2,500 fps striking at around 1,700 fps at 220 yards in 1-in 14" twist barrel gave straight-line penetration at SF as calculated by yourself ... "It is a hair over 2 at 2.04 at 1200fps to 2.09 at 2600fps."

I can support the CIP view, but not your bogus theory.

Warrior

yes,
We are still looking for a dealer in Scandinavia. The only way at the moment is to order direct from us. Post is quite reliable into Scandinavia. I recall only one problem but it was related to someone who had moved and the parcel was returned to us somewhat beaten up. If anyone is interested in taking up the dealership they should contact Gina and discuss.

Chris Bek,
As with your confusion over "deep" and "straight" on the other thread, here your difficulty is in distinguishing between "a theory" and "a specification". Can your fave bullets meet the GSC dimensional and weight specification? No they can not. Why then are you so bent out of shape when other specs GSC place on their products are also not met. I do not care what you or any other manufacturer specifies as a parameter for their bullets, that is your and their choice to make. Our specs have ensured the continuing success of our bullets and, regardless of how you thrash around about it, it will not change. Get over it.


theory
Noun
pl -ries
1. a set of ideas, based on evidence and careful reasoning, which offers an explanation of how something works or why something happens, but has not been completely proved: the theory of cosmology
2. the ideas and abstract knowledge relating to something: political theory
3. an idea or opinion: it's only a theory, admittedly, but I think it's worth pursuing
4. in theory in an ideal or hypothetical situation: in theory, the tax is supposed to limit inflation



specification
Noun
1. a detailed description of features in the design of something: engines built to racing specification
2. a requirement or detail which is clearly stated: the main specification was that a good degree was required
3. the specifying of something

How typical of you to base such overwhelming conviction of opinion on one shot. "Proof of Bogus Theory" is only proof of the fact that you have no grip on reality.

On the subject of rifling/twist, it was stated that the hammer forged method probably produces a truer twist rate than that of button method. I would vouch for that and reason is simply watching button type barrels mfg. and the twist is created by a gear driven apparatus as the button is forced down the bore. Change gear ratios and you change the twist rate. Well the gear driven system produces whatever twist you desire as long as the gears/teeth/ gear tooth roots, etc. of the actual gears are 100% in spec and over a period of time wear sets in and of course that alone can cause a variation in the twist result.
Have been told though that the variance will only be 1 plus or minus of the desired twist. If you want a 10 twist you may well end up with a 9 or 11 or even something in between. Does that make a difference on a hunting rifle performance, well, yes it could I suppose, but most hunters will not know the difference at hunting ranges w/ hunting loads.
As for long range match shooters they prefer the cut rifling system and one of the reasons given is that the twist can be exact and what they want for their particular caliber/load. One of the reasons many match shooters will opt for the Krieger or other cut rifled barrels. As pointed out, variance of more than 1 ratio in twist would be a problem I would think and performance would not be what you expected with a particular bullet weight, velocity, etc.

I used to remember the formula for RPM of a bullet with a given twist, velocity, but can not remember or find, anyone out there care to share that info?? Thanks

quote:

How typical of you to base such overwhelming conviction of opinion on one shot. "Proof of Bogus Theory" is only proof of the fact that you have no grip on reality.

Gerard,

I quoting from the other thread where I posted this ...

"Here is another real life comparison, the 9.3/286 gr Rhino Solid yields a SF value of only 1.39 with a standard twist of 1-in-14". It provides straight-line penetration, as confirmed by various PH's despite the fact of a lower SF value. Likewise, many buffalo have been shot with the .416/400 gr Rhino Solid at 2,400 fps in a standard twist of 1-in-16.5" yielding a SF value of 1.44. This is proof that a SF value between 1.39 and 1.44 is adequate both for Softs and Solids, as straight-line in-target penetration is not governed by the twist rate, but rather by the geometry of the bullet."

Gerard only in your mind is my example ONE SHOT, even though you read it. Are you smoked or are you going senile?

Warrior

So, you remain confused about "theory" and "specification".

quote:

Have been told though that the variance will only be 1 plus or minus of the desired twist. If you want a 10 twist you may well end up with a 9 or 11 or even something in between.

dsiteman,

The marginal drift you mention above makes sense, and probably only happens in your country. I seems much much worse her by us according to Gerard who wrote ... "I measured the rest of them and the batch varied from 1:7.5" to 1:11". I sent 13 barrels back that were useless as 7x57 barrels." He rejected 13 out of a batch of 25, that is more than half !!! Sounds like a fisherman's tale.

It seems things only happen in the extreme here by us. Gerard silence on my question on this subject makes me wonder if this is not perhaps a figment of his imagination. I have experienced how he can twist things to suit him. I would actually love to follow this up with the manufacturer that puts barrels out like this. I have dealt with 2 barrel makers in SA, and I can assure you not one of them puts barrels out like that in my own experience and from all my buddies that had custom rifles built. I suppose I can phone custom gun makers and survey their opinion as to their experience.

Warrior

quote:

The marginal drift you mention above makes sense

This is typical of our differing outlook. To you, a barrel that is supposed to be 1:10", but is in fact 1:9" or 1:11", is a "marginal" difference. I say that, if I have ordered a 1:9" barrel, it had better be between 8.75 and 9.25, if it is a hunting barrel, or it goes back.

quote:

I have dealt with 2 barrel makers in SA, and I can assure you not one of them puts barrels out like that in my own experience and from all my buddies that had custom rifles built.

With your "marginal" standards I am not surprised that you do not notice. Been there done that with your fave barrel maker too. To their credit, the last time I ordered one from them, the twist was right but the bore/groove was off. The second one they sent me was spot on.

The problem is not peculiar to our barrel makers. I had a Schultz & Larsen 7x61 rifle here that was stamped 1:10" on the barrel, but measured 1:11.5". Measured a pre 64 Winchester a couple of months back that was so far out, I measured it three times to be sure.

quote:

Sounds like a fisherman's tale. Gerard silence on my question on this subject makes me wonder if this is not perhaps a figment of his imagination. I have experienced how he can twist things to suit him.

You always demand that I prove everything I say but take everybody else's statements as they come. When I present proof after your accusations, there is not a word of apology. But nooooo! There is no agenda! Take a running jump you despicable Troll.

I see you remain confused about "theory" and "specification".

quote:

You always demand that I prove

Give the details so I can follow up on the barrels that you claim were so wildly out. That will be the proof.

Both my Truvelo barrels are perfect and they measured perfectly made by Jaco van Vuuren.

Warrior

What form will the apology take?

Lets deal with the facts first, you have lied so much to me before that I am willing to take you on. I will give you a public apology if I am wrong. Now give the exact details so I can follow it up.

Warrior

Name two instances where I have lied to you.

Let us get on with the facts, so we can see if there is another lie. Let us not get side-tracked now in another ad-infinitum debate in futility.

Warrior

I will give you the proof as soon as you post two instances where I have lied to you. That is just another old saw you use, which is in itself a lie.

Providing proof is easy. You forgot that gunsmiths and dealers keep registers and supplied monthly (now weekly) reports to CFR, didn't you?

Jump through the hoops, Troll.

Gerard,

Step up or step back.
If you are confident, let's go.

Warrior

Not to prolong the "debate," but discussing the twist factor with Sierra some years ago, I was told that a difference of twist being 1 would impact on performance some few thousands of predictable accuracy?? Believe their manual discusses the topic to some degree and shooters whether they be hunters or military all over the world consider them as a "source."
As for barrels and their twist, recently purchased a Tika T3 Tactical which advertizes a 11 twist for the 308 caliber and believe it is a hammer forged barrel and from all I can determine it is spot on at 11. Crude method of measuring with yard stick and marked cleaning rod in inches, but seems to come out to 11 after several tests. Would also add that doing my so called break in period, quit after 10 rounds for the bore is mirror and no copper to be seen or tool marks via a Hawkeye Bore Scope.
I assume Tika/Sako mfg.'s their own barrels in their facilities and if you have not taken a look at one these rifles, might want to check them out. Ideal size, weight, balance, outstanding accuracy, and very much likes the Sierra 175 HPBT MK bullet.

The twist requirement for extreme accuracy (bench and long range paper punching) is more critical than for hunting at normal distances. The twist rate should match the bullet type and length and both must be optimally suited to the distance for ultimate accuracy. There is the additional factor, with jacketed bullets, that there must be just enough gyroscopic stability for stable flight. Anything more may enhance any ecentricity in the bullet and that will open up groups. Making a bimetal bullet perfectly concentric is a frightfully dificult task. Hats off to those who succeed well at this.

I like Tikka rifles too. The simplicity of the bolt design is good and the action is very rigid.

Hi gerard
What is the name of twist checking device? do you have any technical data for that twist checker?
regards
yes

Gerard,
If your up for it ... in your experience how does the Greenhill formula relate to monometal projectiles? Reason I ask is that there is a built in assumption in the formula of a specific gravity of 10.9, plus a velocity in the range of 1900fps to 2600fps from memory. As we start moving internationally towards monometals due to concerns with lead ... will traditional twist rates need to be tightened, or will shorter/lighter monometals result?? Regarding Tikka rifles, I was surprised they only use a 1:14" in their 9.3x62's ... seems very close to borderline with a long 320gr Woodleigh particularly an FMJ.
Cheers...
Con

yes,
I put together a page that shows how the twist checker is used and also how to make one. It is very easy, have a look.

Con,
Greenhill does not work well with copper monos. It also has no provision for entering a number of parameters that will affect the stability factor of the bullet and, therefore the twist rate required for a given S/F.

On the Usefull Stuff page of our website is a download that will give you a better means of calculating the requirements of twist and bullet length. Left hand column, six blocks down.

Going from lead core bullets to copper monos require only a drop in weight. Bullet length remains very similar. Some applications work better with shorter than "normal" length monos. Be guided by the manufacturer.