Pick up a copy of "balistics in Perspective" by mike LaGrange

His maths may not be up to scratch but the field performance on 22,000 elephant is hard to argue with

When shooting my 300 mags,the bullet holes on the paper target are smaller out of my Krieger barrel compared to the factory Winchester barrels.Accuracy is better in the Winchester barrel.

I apologize if I missed it but could somebody explain why the Barnes RN monos tumbled and deviated the worst in my penetration tests in water? This was with the 500 grainers from a 1-14" .458Lott at 2250mv and approximately 20' to surface of water.

They were, by far, the poorest penetrators, never recording three linear feet within a 24" square and always at least moderately sideways through the test baffle at one foot and always significantly sideways at two feet.

Thanks!

PWS,

1. They are too long to properly stabilize with your twist rate.

2. The hemispherical round nose of the Barnes that you tested seems to be the absolute worst nose shape for penetration depth.

Another way of saying it would be to say that the sectional density is too high.

quote:

Originally posted by Gerard:
Another way of saying it would be to say that the sectional density is too high.

True statement but it only applys to monometal bullets.

465H&H

Not trying to but can someone clarify what velocities and forces cause the long, hemispherically nosed Barnes to destabilize so quickly in a media denser than air?

I've learned enough to grasp the effects of twist rate: that greater a higher rpm dampens "yaw" more and lessen the angle of incidence upon impact, but, I get lost if twist, and hence dynamic stability, is determined exclusively by bullet weight without a factor for form. Intiutively, it's obvious that a 1lb steel rod, 12" long is much less statically stable than a 1lb steel rod 1" long; where is the difference dynamically?

Again, thanks for the replys!

quote:

True statement but it only applys to monometal bullets.

Nope, applies to all bullets, jacketed lead bullets as well. How do you think you will do with a 30 caliber with a 1:12" twist and a 200gr or 220gr cup and core bullet? Or maybe a CIP spec 416 Rigby with a 450gr lead core bullet? Which would be the better choice for a 458WM, a 550gr lead core solid or a 500gr lead core solid? Try shooting a standard spec 22-250 with a 70gr lead core bullet and all that sectional density will render it useless.

Sorry Gerard but it is not the sectional density that causes stability problems in the calibers and weights you mention. It is the length of the bullet. If you make the same bullets out of more dense metals such as tungsten or depleted uranium they will be shorter and have the same SD but will stabilize. That is the problem with monometal bullets. They are made out of low density metals that require you to sacrifice bullet weight to get stability or you must put on a new barrel with a faster twist on your gun. That costs $$.

In the 458 Win the 550m grain steel jacketed solid stabilize just fine out of the 1 in 14 twist. The problem is that they can't be driven fast enough for optimum penetration with the Wins case capacity. My 458 Lott with 550 Grain Woodleighs @ 2,150 fps will shoot into an inch at 100 yards and penetrate over 70" in elephant and do it in a straight line. That shows they are stable in both air and flesh.


465H&H

Ok, I'll admit I was being lazy so I went back through the thread to answer my own question as to why the Barnes RN mono performed the worst in my rudimentary tests. Please correct me if I'm misled.

The Barnes mono RN is gyroscopically stable in air with standard twists and velocities but, a bullet can be gyroscopically stable in flight AND travel with a large angle of "yaw". ("yaw" being a blanket word for "not straight on"). The rotation velocity of the flying bullet is adequate to overcome any overturning moment encoutered in flight but, and for all spin stabilized projectiles, woefully inadequate immediately upon impacting a denser media. In addition, the round nose does nothing to counteract the tremendously larger overturning moments encountered upon impact and the bullet quickly overturns in the denser media.

So, the Barnes mono IS too long (SD too high for the bullet's media?) and although stable in flight, it's larger "yaw" and geometry result in wild penetration characteristics. In addition, even though twist is typically derived primarily by bullet weight, factors such as geometry, density of bullet media, and density of media traversed also come into play in bullet stability.

Time to revisit the gyro theorem!

PWS,

I think it can be broken down into 2 factors.

1. Bullet too long (or twist too slow for the bullet) = too much yaw = early tumbling, including tumbling on impact with the animal. Even if not tumbling, the bullet with excessive yaw experiences greater lateral friction than a bullet entering straight on.

2. Hemispherical RN = small supercavitation bubble = shallower penetration. Intuitively it would seem that a hemispherical RN would tend to roll off hard objects, while a FN would tend to bite in, but the mechanism at work a 2400 fps may be quite different than we would imagine.

For information on the supercavitation bubble, please see http://www.grosswildjagd.de/penetrat.htm



[Rhetorical question: Can Alf resist the urge to respond? ]

super penetrator=500 grain failsafe.Probably kill two elephants at once! Or a whole herd of buffalo!

/

hmmmm...

your logic is somewhat intact but why then the need for the 6.8 spc and 6.5 grendel that the special forces are clamouring for...

/

quote:

but why then the need for the 6.8 spc and 6.5 grendel that the special forces are clamouring for...

These 2 new calibers address a somewhat different situation that the military is faced with. Desert warfare conditions in Iraq and Afghanistan is in many ways different than in Vietnam. Also there is a need for harder targets to be penetrated (like shooting through automobile glass & metal) and one thus needs more power. That comes in large part by increasing bullet mass- 55 grains vs 123 grains. Also, the higher BC bullets of the 6.5/6.8 mm caliber becomes important in that the bullets trajectory is flatter at longer distances and it resists wind deflection better. The military has conducted accuracy & penetration tests from 300 to 600 yards and are very happy. At these distances the diminutive 5.56 mm bullet does not compare. I would be very interesting if we could get to see these comparative tests.

Warrior

/

465H&H,

quote:

it is not the sectional density that causes stability problems in the calibers and weights you mention. It is the length of the bullet.

When bullets of similar construction are made longer the Sd increases. I have been told this by very knowledgable people. If bullet is too long for a particular application, surely it means the Sd is too high as well.

However, if we compare bullets of dissimilar construction, as you do with monos and cup and core, then we could also say that the problem with cup and core bullets is that the material density is too low, compared to depleted uranium bullets. It is important to choose the bullet length correctly and with consideration for the bullet construction rather than to blindly choose a bullet by Sd.

quote:

That is the problem with monometal bullets. They are made out of low density metals that require you to sacrifice bullet weight to get stability

From your point of view, the glass is half empty. I would restate that to read: That is the advantage of monometal bullets. They are made out of low density metals that allow you to take advantage of lower bullet weight and have good stability as well as greater terminal performance reliability.

You mention a good example here:

quote:

The problem is that they can't be driven fast enough for optimum penetration with the Wins case capacity.

In this example, excessive sectional density (length) robs needed case capacity. Another disadvantage of Sd and another reason to choose one's bullets wisely and not based on which has the greater Sd.

/

quote:

It is important to choose the bullet length correctly and with consideration for the bullet construction rather than to blindly choose a bullet by Sd.

I very much agree with Gerard on this one.

Shooting bullets that are too short or too long always brings with it compromises. For example; shooting bullets that are too short (stubby in appearance) in a setup like what we have in long-throated European calibers, such as like 7x57; 7x564; 9,3x62. Also if the bullet is too short, it creates unnecessary space in the magazine box for the bullet to pick up inertia when the shot is fired and so bump the bullet tips with the risk of knocking the bullet further into the case, which could result in disaster in high recoiling rifles. Also with a bullet too far away from the lands it may affect accuracy adversely for one, whilst the short bullet may not get sealed properly and then one suffers blow-back. Bullets need to be seated deep enough into the case's neck so that there is enough purchase on the bullet to hold it steady - so there is a "war" between this condition and getting closer to the lands. Also generally short and stubby bullets lack good BC's as opposed to more sleeker designed bullets. So greater SD will assist, but the sleeker shape to make it more aerodynamic (less air drag) must be added, so one drives the BC score up on both counts.

Shooting bullets that are too long on the other hand robs the cartridge case from its powder capacity, and hence you suffer a velocity drop-off. This is particularly a problem in short-throated calibers, such as the .308 Win and 375 H&H. In the .308 Win one is seriously limited with its standard twist rate of 1-in-12" and thus the top-end is around 165/168 gr bullets for adequate stabilization, whereas the 30-06 (same bore as .308) with its faster twist can stabilize 220 gr RN bullets. However the "overly fast" 1-in-12" twist of the .375 H&H presents no stability problems at all with heavy bullets, but the sacrifice is in velocity and one has to revert to duplex loads. Now some buffalo hunters do not mind this extra effort, nor the fact that the bullet is seated deep into the case. All I am saying is, this is not an ideal position from a design point of view. The long for caliber 380 gr RN Rhino bullet kills like the hammer of Thor - terminal performance is not in question in the area of killing, but one is limited in terms of lower velocity, more bullet drop and a shorter application range (distance). In other cases such as the 30-06 there are some people that want to shoot 250 grain bullets and invariably they will find that it does not stabilize properly - the bullet is simply too long for the 1-in-10" twist.

So bullet length rules in terms of clever design to match bullet length with magazine box dimensions, with length of free-bore, and last but not least (seen from another angle), mass to bore ratio (SD), as it also relates to the internal ballistic event, affecting one's choice for the correct propellant. For example, shooting a lighter bullet in a 7x57, such as a 130 gr HV bullet will give you better results with S335 (fast-burning) as opposed to S365 (medium slow-burning), which is better applied to the heavier bullets in the range of 160 to 175 grains.

However we should never blame SD for the ills in the set-up if the rate of twist is too slow. That is another decision entirely, as it depends on the barrel that was fitted.

Warrior.

Comments in quotes are from Gerard!

quote:

When bullets of similar construction are made longer the Sd increases. I have been told this by very knowledgable people. If bullet is too long for a particular application, surely it means the Sd is too high as well.

Not completely true We can make a bullet longer by changing the bullets shape. Compare a RN solid to a pointed sold. The mass and SD stay the same but the bullet is longer and therefore less stable assuming a similar rate of rifle twist.

"However, if we compare bullets of dissimilar construction, as you do with monos and cup and core, then we could also say that the problem with cup and core bullets is that the material density is too low, compared to depleted uranium bullets."

If the bullets are already stable how can you get more stability with a denser bullet material? Stable is stable by definition.

"It is important to choose the bullet length correctly and with consideration for the bullet construction rather than to blindly choose a bullet by Sd."

I completely agree with this statement. The main reason being that Sd does nothing to predict stability unless bullet shape and length and construction are also considered.

"From your point of view, the glass is half empty. I would restate that to read: That is the advantage of mono metal bullets. They are made out of low density metals that allow you to take advantage of lower bullet weight and have good stability as well as greater terminal performance reliability."

First let me say that I am not in anyway anti-mono metal bullet.
In fact although I have only used steel jacketed solids on DG in the past I may switch to a mono metal solid in the future in my 470 double.
But the switch will not be for any of the perceived advantages you have given above. I do not agree that mono metal bullets always give greater terminal performance than steel jacketed bullets. Both mono bullets and RN steel jacketed solids have their advantages and disadvantages.
A good hunter will know what they are and use the type of bullet that best serves their needs.

"In this example, excessive sectional density (length) robs needed case capacity. Another disadvantage of Sd and another reason to choose one's bullets wisely and not based on which has the greater Sd."

As ALF so ably and in a much lesser way I have been trying to explain to you it is not SD that causes the stability problems. It is bullet length. One more try. You can increase a bullets SD by changing the density of bullet material or the shape of the bullet and if this makes the bullet shorter it will be more stable than the original bullet even though the SD goes up. Get over your SD fixation, concentrate on length and you will produce a more stable bullet.

CHEERS!

465H&H

465H&H,

quote:

Compare a RN solid to a pointed sold. The mass and SD stay the same but the bullet is longer and therefore less stable assuming a similar rate of rifle twist.

This is what I said on the previous page (post of 15 April) where I said:
"So a practical comparison of bullet lengths of the same caliber shows:

Caliber - Weight - Twist rate - Bullet length - Stability Factor - Shape
270 ----- 150gr -- 1:10" ------ 31.2mm/1.23" - 1.44 @ 2600fps -- SP BT
270 ----- 150gr -- 1:10" ------ 26.8mm/1.06" - 2.07 @ 2600fps -- RN FB

A stability factor of 1.5 can be had with the Round Nose Flat Base bullet in a twist rate as slow as 1:11.3" while the same weight Spitser Boat Tail needs a twist of 1:9.5" for a stability factor of 1.5."

quote:

If the bullets are already stable how can you get more stability with a denser bullet material? Stable is stable by definition.

Stability can be of a lesser or higher degree. You say so yourself in the first line of your post that I quoted above. ("the bullet is longer and therefore less stable") I guess you answered your own question before you asked it.

quote:

As ALF so ably and in a much lesser way I have been trying to explain to you it is not SD that causes the stability problems. It is bullet length.

I know this. See my post of 15 April previous page. I am simply pointing out that the Sd fans cannot have it both ways. When performance is enhanced, Sd is praised as the reason for these improvements even though the connection is nebulous and sometimes a stretch of the imagination. When bad things happen as a result of excessive Sd, suddenly Sd is no longer the prime driver/reason/magical quality.

Some design specs are such that one just cannot use a high-SD bullet in them, even if you desired so. Here are some examples :-

.243 Win with a 10"-twist --- 100 gr bullet; SD = .242
.270 Win with a 10"-twist --- 150 gr bullet; SD = .279
.308 Win with a 12"-twist --- 168 gr bullet; SD = .253

Obviously with custom barrels with faster twists one could engineer to use heavier bullets (higher SD), but the extra length would again be limited by very short throats in all of the above calibers. That is why I believe cartridge design must be done from the ground up as to what you want to achieve.

For example, the Germans designed the 9,3x62 for their colonists in Africa as an all-round African cartridge to hunt mainly game for the pot. It is well designed with complete ballistic balance imo - a long throat to take advantage of a longer bullet (higher SD), twist relatively slow but fast enough for its designed/intended bullet weight, just enough case capacity to achieve modest velocity for its intended bullet mass at a relatively modest pressure level. It is not over-designed in any respect, but with some lee-way to use heavier bullets - here it is:-

.366 Cal with a 14"-twist --- 286 gr bullet; SD = .305
.366 Cal with a 14"-twist --- 300 gr bullet; SD = .320

The whole idea was to get a bit more mass behind its frontal area for one, and to pick a bullet mass heavy enough so that buffalo and elephant could also be taken on occasion.

Warrior

/

Alf,

Excellent explanation - the question is not less understood

Warrior

I stand corrected by ALF. I forgot the affects of different Centers of Gravity on bullet stability.

ALF,

Where would the dart shape fit into your continuum of bullet shapes relative to stability?

465H&H

/

quote:

Originally posted by 500grains:

quote:

Originally posted by Buliwyf:
The Barnes solids are not "overly long". They will stablize just fine. Rifling is based on bullet weight not length.

Nope.

dan is right in this matter, correct twist is a result of bullet length. Clearly defined in/by greenhill

quote:

Originally posted by jeffeosso:

quote:

Originally posted by 500grains:

quote:

Originally posted by Buliwyf:
The Barnes solids are not "overly long". They will stablize just fine. Rifling is based on bullet weight not length.

Nope.

dan is right in this matter, correct twist is a result of bullet length. Clearly defined in/by greenhill

why not weight??? if one has a polymer tip on it and thus longer but identical weight that throws this theory off.

Bullet weight determines determines twist.

When have you ever seen a loading manual list bullet lenght?

Buli,

The 400 grain Woodleigh RN stabilizes just fine out of a 416 Rigby. But the 400 grain Barnes X often tumbles when game is hit.

What is the difference between the two?

Bullet length.

500 grains:

Thanks for a civil tone. Woodleigh are conventional construction. Barnes are hit and miss regarding accuracy in all calibers depending on rife. Barnes are of course longer in equal bullet weight because of lighter copper construction.

Bullet weight determines the rifling twist and expected impact velocity determines bullet construction. These are the two important drivers.

/

Buliwyf,
Do you agree with this?

quote:

Caliber - Weight - Twist rate - Bullet length - Stability Factor - Shape
270 ----- 150gr -- 1:10" ------ 31.2mm/1.23" - 1.44 @ 2600fps -- SP BT
270 ----- 150gr -- 1:10" ------ 26.8mm/1.06" - 2.07 @ 2600fps -- RN FB

A stability factor of 1.5 can be had with the Round Nose Flat Base bullet in a twist rate as slow as 1:11.3" while the same weight Spitser Boat Tail needs a twist of 1:9.5" for a stability factor of 1.5.

quote:

the gyro no longer functions (actually it stopped functioning shortly after penetration)

In-target drag is too high for it to function, as SF values are an air-drag function.

Warrior

quote:

Originally posted by boom stick:

why not weight??? if one has a polymer tip on it and thus longer but identical weight that throws this theory off.

what is the density ratio (relative density) between copper and plastic...

in other words, there is no "worthwhile" effect, from a twist POV, if a plastic nose.

however, there IS one worth considering on a plastic bullet.. the plastic filled 7.62x39 is a case in point...


Alf, we totally agree... greenhill assume copper jacketed lead bullet.. however, the TWIST rate resulted will send a barnes bullet down range fairly well, so there is enough inherent fudge factor to accomplish shooting barnes bullet accurately..

btw, i have yet to see a modern rifle (made in the last 60 years) WITHOUT A KNOWN TO SLOW TWIST, that won't shoot barnes bullets well, if the loader will do one simple thing

read the directions on the bullet box and seat the bullet way WAY back.


As for barnes bullets tumbling, and that being a function of twist...

well,

Remember that the same tests show the north fork FN and the Bridger bullets to penetrate best of all...

and those are shot from the same twist rifle that the barnes don't penetrate well from...


and the northforks and bridgers are made from a LIGHTER material than barnes, and are therefore longer.


However, someone said it well... nose design


DO bullets yaw? NO, they helix....

but i am begining to yawN on the PII

/

There are significant differences in the design of flat nosed mono-metal bullets. A FN with a small meplat and a large and long taper may have it's CG much farther to the rear than a comparable weight RN solid. This could mean a less stable bullet.

465H&H

Perhaps it is our inadequate semantics but when the statement is made that "a longer bullet has less stability", what is implied is that physical length allows a longer moment arm on the CG upon impact (which contact typically occurs at the nose)?

A more strict way of describing "lesser stability due to length" would be (to roughly paraphrase Alf) "mass distribution within the bullet away from the center of gravity and the resulting increased lever arm operated by the drag forces that overturn the bullet".



I'm very curious to read how the new Hornady FN-FMJ performs as RN FMJ have have been the standard for so long. Will the addition of the slight FN profile to an FMJ address the RN's minor shortcomings? It appears that the FN on a solid has firmly established it's benefits!

quote:

There are significant differences in the design of flat nosed mono-metal bullets. A FN with a small meplat and a large and long taper may have it's CG much farther to the rear than a comparable weight RN solid. This could mean a less stable bullet.

465H&H,

Could you please give us a better appreciation of where the CG point sits with the Solids like Bridger, NF, GSC, Barnes, A-Square, Rhino Solid, Dzombo Solid, Wdl FMJ,Hdy FMJ and any other that you have evaluated?

The centre of gravity point of the Barnes Banded Solid should be as near in the middle as is possible for a RN design with a flat meplat.




Warrior