Uh, Clark, wrong about what? I doubt your average 1:10 twist will stabilize your average 175-190 gr. 7mm bullets at 7X57 velocities. 1:9 will stabilize lighter/shorter bullets. See the posted photos above regarding practical results. What does bullet imbalance and projectile jump have to do with the posted question?

As I responded to Allen, the fella wants to shoot heavy/long bullets and with that constraint a 1:10 twist is simply not the answer. Now if you fellas want to convert him to mainstream philosophy and conventional wisdom concerning proper bullets for the 7mm bore have at it, but that is a different issue.

i was talking to a gunsmith the other day and he mentioned somethnig concerning the twist rate in a barrel. i want to get a 7x57 barrel with a 1:9 twist for use with heavier and longer bullets. he said that i should be careful to not get too fast a twist. he went on to say that if the twist is too fast, it may cause accuracy with lighter bullets to fall off. he sounded unsure of why that would happen so i dismissed the remarks.



do any of you know why this would happen or is he just wrong all the way around... if he is correct, what is the lightest bullet i can expect to shoot well in a barrel with a 1:9 twist?



my desire is to be able to shoot 160 and 175 grain bullets, but still not be hampered from shooting lighter bullets as well. thanks for the help..........

Bill

There is absolutely no evidence to support the urban legend that a fast twist compromises accuracy. If that gunsmith has such evidence I would like to see it. If there is any doubt as to what twist might be needed for a particular bullet, always, always opt for the faster twist. This is not to say that you should get a 9 twist if you plan on shooting only 120 grain bullets. But if 175 or 180 grain bullets are in your plans by all means get a 9 twist. The only disadvantage of too fast a twist is when you shoot fragile bullets at very high velocities. In the case of the 7 x 57 I don't think you'll ever run into that situation.

Naw, Bill is absolutely dazzled by the intellectual universe he just stumbled into. And he'll probably have his 'smith build what he, the client, wants.

In the previous post by Alberta Canuck the ballistic term for what he is describing is known as TRACTABILITY . That is the phenomonon that enables a gyroscopically stabilized projectile to keep its pointy nose pointed in the right direction, ie. pitch downward as it follows its ballistic arc. Tractability is a subject of sometimes viscious and rancorous debate amongst the unwashed masses. It is inverse to gyroscopic stability, which in turn is inverse to velocity as I understand it. 500 gr bullets from the .45-70 are tractible to 3500 yards or more, and I read a quote attributed to Robert McCoy that "any properly designed bullet is tractable throughout its flight." Operative word there is "Properly".

http://www.nennstiel-ruprecht.de/bullfly/tractf.htm#header

One facet of this which is of no consequence to any other than long range plinkers is Yaw of Repose, which I mentioned earlier. It is the product of the slight lag in tractability and the sum of aerodynamic forces doing battle with gyroscopic precession. Depending on direction of twist the bullet will either be pointed very slightly right(rt) or left(lt) of direction of travel, and will deflect slightly in that direction.]

That is all.

Cheechako is correct. Go with the 1:9 and don't fret about bench rest quality accuracy issues. There are two issues at hand with fast twists. One, at high velocity you may have bullets come undone due to structual failure, and two, if you're involved in long range shooting there will be a small but definable issue relating to Yaw of Repose. None of this is much of an issue with the 7x57.

If you go with the slower twists you simply won't be able to stabilize longer(heavier maybe) bullets. Stick to your guns, and maybe find a new 'smith.

Your gunsmith was right.

The 7X57, along with quite a few other 7mms, tends to be a very twist-specific cartridge. If you want to shoot mostly 140 gr. bullets, a one-in-ten twist is likely the best way to go.

Some factory 7X57s don't shoot the lighter bullets well because they have long throats and very fast twists (9" or 8.75") and were set up that way to work well with 175 gr. bullets, which almost no one uses these days in the 7mm Mauser. For example, the current CZs in this caliber have extremely long throats that can make accuracy a challenge with these rifles.

AD

A 1:9 twist is what all of the old military guns were supposed to have, which made them shoot heavier 170 gr bullets well.
I however own a M1895 Chilean Mauser with the original military barrel on it.
I figured it would like heavier bullets but for some strange reason it loves the cheap Winchester bagged 150 gr PP the best (under .75 inches at 100 yds).
So, if you are looking for a custom rebarreling job this should not be anything to worry about, however if you are getting a cheap takeoff barrel I would check to make sure it is a slower twist.

-Spencer

Allen, Bill said he wanted to shoot longer and heavier bullets. With that qualifier his 'smith is wrong. What you said is correct outside of that qualifier of course, but Bill will still be able to shoot lighter bullets with the fast twist. As to the throat issue, if you're chambering a barrel from scratch it's no big deal to set it up for a long/heavy SPBT. Or even a 175 RN. He will still be able to get reasonable performance out of a range of bullet styles, and weights. If the throat is cut properly the extra leade won't bother the odd 140 speer or sierra. Bullet bases can protrude into the case, or not, it's not all that important within reason.

I have a friend that built a 7x57 AI and went with the 'smith's advice for a 1:10 twist on a Shilen barrel. won't shoot anything 150 grains and above worth a damn, bugholes the lighter ones though. Last thing he wanted was a gun that excelled with 140 grain bullets.

No one has ever explained to me why it is so important to have a twist that goes all the way from 1 in 8 inches which was on some factory rifles in 7X57 at one time, up to a 1 in 11 inch such as Shilen and a few others offer. Compare this to the good old 270 that no one would think of having anything but a 1 in 10 inch and shoot everything from 100 to 160 grain bullets in it. It makes little or no sense to me. My own 275 Rigby is a 1 in 9.5 inch twist while my Wife's 7X57 has a 1 in 9 inch twist. Both shoot 150s and 160s great, with the only difference being the 1 in 9.5 inch twist shoots them about 50 feet faster with the same load. I have had other 1 in 9 inch barrels that didn't shoot the 140s very well also, and certainly not the 120s. When splitting hairs like this I would probably just use a 1 in 9.5 or 1 in 10 if I was to build another 7X57, because I myself can see little advantage in using the 175 in place of the 160 grainers for most practical reasons. A 175 in a 7X57 is generally moving slower than I would want and very often with a bullet that is not as streamlined. Because of this I would rather use a good 160 grainer as my heaviest load.

I have a 7X57 Model 98 Military Mauser that has the original barrel that I use for Deer hunting. It's had a scope mounted and I just put a Huber trigger on it. I shoot the old Barnes 190 grain bullets exclusively as they shoot very well. No problem with stabilization and dead on every year for Deer hunting. I have the original stock with the forend cut down and glass bedded. The bolt has been lowered and a scope friendly safety installed. I used to use the military two stage trigger, but decided to upgrade this year. It only took me a short time to install the trigger. The Huber trigger is just great, breaking at 2 pounds 2 oz; very crisp too.
Back on track, I think mine is a 1 in 9 twist also. I have enough of the old Barnes 190 grain bullets to last a very long time; I am set for life. That's the only rifle I use for Deer hunting. Looks terrible, but shoots great. I have a Leupold 6X42 on top.
Don

Bill, the first two groups were shot with a 1/9 or 1/9.5 twist in a Ruger 7X57mm. Both with 140-grain Nosler Partition bullets @ 3000 FPS MV.











This last one was shot with a 150-grain Nosler BT in a Venezuelan FN Mauser with a twist of 1/8":



Don't worry about a 1/9" twist-it'll work for all weights in the 7X57mm!!

Bill,
Cheechako, Digital Dan, vapodog, and Savage99 wrong.

Your gunsmith and allen day are right.

Most talk about accuracy is black magic, but the relationship between twist rate, ammo concentricity, and accuracy is mathematically derivable and verifiable.

When the bullet enters the bore, it enters crooked. That makes the center or rotational momentum off the center of the bore. When the bullet exits the muzzle, it veers off in the direction of it's center of momentum. The ratio of the velocity to revolutions per minute of spin determine how far the point of impact will be from the point of aim. This is directly proportional to the twist rate. Because the chamber forces concentricity to within ~ .004", the error is typically only +/- 1" at 100 yards = an extra 2" to the group. Twice the twist rate would make that 4".

The way the accuracy game is played is to get a twist rate fast enough to stabilize the length of bullet to be used, but no faster.

"The NRA Handloader's Guide" 1969, a compilation from "The American Rifleman" 1950 to 1968, article gauging bullet tilt, by A.A. Abbatiello and was based on "The Bullet's Flight" by Dr F.W. Mann and the work of George L. Jacobson of the Frankford Arsenal in 1959:
"Mathematical Solution
The laterally displaced center of gravity moves though the bore in a helical (screw) path. The pitch of this helix is the pitch of the rifling, and the radius is the lateral displacement of the center of gravity. On leaving the muzzle the center of gravity continues in the direction it had at that point. .. The angle of emergence is that angle who's tangent is 2pi times the lateral displacement times the pitch. For a .004" displacement and a 10" rifling pitch, the tangent is 1/8 (2 pi)(.004) / 10 and the corresponding angle is 1.1 minutes.
...The effects which Jacobson found.. are essentially in agreement with the work reported here."


--
A society that teaches evolution as fact will breed a generation of atheists that will destroy the society. It is Darwinian.

For the sake of friendship I assume that is the first mistake of your life? Well, I don't misread things more than once or twice a day. Once after reading the owners manual for a new truck I was surprised to find out the brakes didn't work when the truck was upside down. Really surprised...

Your comments regarding the offset from POA with the non-concentric loads are interesting. I have experienced the same thing in several rifles and as I index the cases with a magic marker I CAN tell you where they will hit regarding clock position ref. POA. The quantity of offset is a bit more problematic to me. I usually segregate varmint loads in increments of .002 RO starting with zero. The difference between each increment is very small, but the difference between .001 and .009 for example is quite marked. Rotating the case 90* off index will cause a corresponding shift in POI. This with 2 Ruger #1's, .22 K-Hornet and .257 Bob, much more pronounced with Bob however.

Clark -



You are, as you usually are, correct.



Here is something else to consider....



One degradation of accuracy which too fast a twist WILL cause is inaccuracy due to bullet attitude at long range.



When a bullet is spun too fast, it still shoots very well on the upward part of its trajectory, because it is still flying "point-on". If spun too fast, however, when it reaches the apex of its trajectory and starts downward, it will not "tip-over" and fly point-on during the downward course of its trajectory. That is a simple gyroscopic effect.



Instead, the bullet will begin dropping, but the nose will still be pointed upward as it was when first fired. That causes increased air resistance and buffeting as the bullet falls, compared to a bullet which DID tip over when it began to fall and is descending point on. It also means it will be less accurate than the bullet which did tip over but still has enough spin to be stable.



The reason this inaccuracy is normally only noticed at long range is that the barrel is pointed up a great deal more for long range shooting, to produce the higher trajectory required. That means the bullet is pointed upward more (pointed up at a steeper angle) than when leaving the barrel in short range shooting. That, in turn, means it has more of the side of the bullet encountering added buffeting and wind resistance when it falls with its nose still up at a steeper angle.



Of course, as there is a very slight decrease in the rate of spin as the bullet flies, one still does want to have enough spin to continue bullet stability at long range, so a very slightly faster twist than the ideal for a particular length of bullet fired at 100-200 yards may be desired.



And, of course, most know that bullet weight is irrelevant in determining the ideal twist. It is bullet length that is important. That in turn is why the ideal twist for a Barnes -X bullet is a quicker twist than would be ideal for a Nosler Partition of the same weight. The Barnes-X would be a much longer bullet if it was the same weight as the Nosler Partition..



Alberta Canuck

In non bolt actions, it is possible to conrtol the orientaion of the cartridge, with an eccentricity pen mark, or putting the letter head straight up.


I learned the expander ball is pulling the necks crooked, but the sizer die without the exander ball cannot fix the crooked brass. The brass must be fired again, and then the die without the expander ball can correct the .004" of crookedness measured at the bullet ogive.

Gentlemen,

This thread has gotten a little off course and I'm sure Bill with the 7 x 57 is wondering what happened. I have just a couple more things to add and then I'm gone.

First, we're talking about a 7 x 57 here.Much of what you guys have talked about may apply to benchrest long range rifles but would hardly be relevant to a 7x57 hunting rifle.

Second, the discussion about accuracy in a military rifle is hardly proof of anything. A 3 inch group with 175 grain bullets out of a 9 twist is no better than a 3 1/2 inch group with 140 grain bullets out of the same 9 twist.

Finally, Alberta, I think you are giving way too much value to that high angle of elevation required for long range shooting. Most 1000 yard cartridges require less than 1/2 of 1 degree elevation, hardly enough to result in a noticable difference in accuracy due to the bullet nose being unable to turn down at the height of trajectory.

Ray

Welllll.....there seems to be a difference of opinions here....and with all due respect I'm sticking to mine.....
I repeat: For a 7 X 57 and (especially) as stated the heavier (160-175 grain) bullets The 1 in 9" twist is what I'd recommend. It'll handle the 175 spire points and do a fine job on the 139 grainers as well.....Been there and done that!!!

If I could get 175 grain spitzers for the .270 I'd build one on a 1:9" twist barrel tomorrow.

vapodog



Just a couple of quick questions if you would.



1. How much longer is a 160 grain 284 bullet than a 150 grain 270 bullet of the same configuration?



2. What do you recon you would get for velocity with a 175 grain bullet in a 270 with a 24 inch barrel with a 1 in 9 inch twist? Every time I have tried a faster twist I have found the velocity to be less than a slower twist using the same bullet.



Many thanks

Well, Cheechako, I think you may be reading more into my comments than was actually there.



I did not at any point indicate that there was a great deal of inaccuracy caused, but simply stated the often proved fact that "overstabilization" does have a negative effect on long range accuracy. The affect becomes more noticeable when shooting into a head wind, of course, and depends on other things too, such as the velocity and trajectory height of the bullet.



None-the-less, it is detectable at long ranges, and does exist. Whether one chooses to allow for it when choosing a twist rate is, of course, a personal decision.



Personally I do not bother to consider that effect, at least for hunting rifles, but as one or more of the other participants in this thread indicated they did not understand the role of twist in accuracy, I thought I might as well explain one of the aspects of too much twist which DOES have a measurable influence in producing inaccuracy.



Half a degree is 30 minutes of angle, and that amount of disorientation can produce a substantial amount of effect on bullet flight.



I'm pretty sure you will agree that the .308 is a pretty commonly used cartridge at 1,000 yards in the "high-power" game. In my rifle I used on the 1979 Palma Team, I needed 37-1/2 minutes of "come-up" from my 300 yard zero to shoot at 1,000 yards. Total angle from the muzzle was well over 40 minutes, or closer to 3/4 degree than "less than 1/2 degree". For the 147-to-155 gr. bullets used at the 800, 900, and 1,000 yards of the Palma, I got my best accuracy with tight bore (.2985"x.306") 1-in-14" twist Sportco or Shultz & Larsen barrels. One turn in 10" did not shoot near as well for me (and many, many others) with those light bullets.



Of course, if one does not choose to add to their understanding of one of the variables contributing to accuracy/inaccuracy, they are certainly within their rights to disregard the information.



They might want to stick to hunting rifles though, and stay away from a career as an artilleryman, should that option occur. <G>



Alberta Canuck

An thought regarding your observation about velocity vs. twist. You cannot logically compare this as each of those barrels is different in fundamental ways that affect velocity, such as chamber dimensions, bore/groove dimensions, barrel length etc. Rifling twist does affect velocity but the effect is VERY small, somewhere in the .5-1% range of energy being used to provide spin to the bullet. The difference between a 1:10 and 1:9 twist as relates to velocity probably cannot be measured even if all else is equal.

Don't mean to get in the way of your question to vapodog...I'm bored witless at the moment.

.

In the higher velocity varmint calibers like .220 Swift AI, etc., a quick twist will slow them down a bit as a rule. I'm not sure that it would be of any consequence though.

I'd expect 2,700"/sec



This may be a practical expectation although shooting 160 grain bullets in a 1 in 10 inch twist tells me it might not be easily attained. Not to muddle things further, but I am curious as to what advantage this is over a 30-06 shooting a 180 at over 2700 in a standard twist which also works well for several other bullet weights.



However, may I ask how much velocity loss you have experienced by using the faster twist



I didn't do a good job of asking the question without fully stating my findings in detail. I have seen several instances where 50 fps and sometimes even 100 fps or more could be attained with a slower twist. Part of this is no doubt because it seems, to me anyway, that a slower twist will take heavier charges of powder before maximum pressure is reached thus giving a better velocity.



The greatest variation I have ever seen was on two nearly identical 30-06s that were built for someone who had more money to play with these sort of things than anyone else I have ever known. He wanted to see what he could get out of a standard 30-06 shooting a 200 gr bullet so he had two identical rifles built and he had everything done to them he possibly could to make them shoot "Fast and True". Both were the same action, same barrel maker, and put together by the same gunsmith with the twist the only difference. Shooting a 200 grain Nosler Partition with a VERY healthy dose of IMR-4831 the 1 in 12 inch twist bested the 1 in 10 inch by over 250 fps. I don't remember for sure what the powder charge was on the 1 in 12 inch barreled rifle but it is safe to say you won't find it in any loading manual. Now, I realize there can be a difference in barrels, and how much of the increase anyone wants to attribute to a FAST barrel is up to them. However, I certainly don't think it was all due to that!! I might also add that the rifle in question cracked at least 3000 fps on seven different chronographs, one which was mine, one afternoon and extraction was not difficult at all. I have never witnessed another feat like this in a 30-06 and I am not about to try and duplicate it myself even if I have the same smith put together the rifle. It was impressive though.

Hello Amigo,

The standard twist (CIP) is 1 turn in 8.66". This was designed for the long 173 gr bullet it was designed for. So rounded of to 1-in-9 is fine. Shorter and lighter bullets came much later and is about the only std factory offering in the States. RWS stuck to the heavy bullet. If you change away from the heavy bullet with its modest velocity, you change the whole character of the cartridge. It looses its bullet performance when you change to a 140 gr bullet and you basically turn it into a 270 Win.

I like to keep my cartridges traditional and do not fancy the idea to shoot 2 or more bullet weights in my rifle, change the scope and readjust to a different trajectory level.
That's it for now.

Dan-Got in on this late.When did Shilen start making 10 twist in .284? I have been going to other makers to get the 10. This is what I use on my 280 AI's and they will shoot up to 175 grainers with no problems. The 11 twist shilen that I built would shoot anything up to 162 grains fine.As far as I know Shilen has not built any tubes with a 10 twist,just 9 and 11.