twist rate and bullet length

[alinwa]

As far as I know the bullet doesn't care what the temperature is except for air density...........
.

This is how I feel too. I think it's important that you keep your loads at the temperature which most closely approximates your hunting conditions.... but WARNING!! If you do work up loads in cold weather, with the powder cold, you WILL experience pressure excursions if you shoot those loads in warm weather. And although the term "pressure excursions" looks benign in print, in real life it means bad things.... like popped primers, busted triggers, even burnt face and eyeballs.....

I'm all about shooting what'cha' got in whatever God gives ya' for weather but it is my opinion that "temperature insensitive powder" is a myth. Be careful with those cold weather loads.

Now....once you've taken the powder load out of the equation...... Once you've set yourself up so your velocity is where you want it...... then it is further my opinion that fatter air, thicker air, colder air, denser air is harder to stabilize bullets in. Shucks, you get up over 5000ft and you can do all sorts of cheating. AND you'll shoot the smallest groups of your life!

For me I found this out the hard way when I loaded up hunnerds and hunnerds of rounds for squeerrel splatting and when I got to the shooting grounds it was 5000ft HIGHER and 40 degrees WARMER than at home. I was zero'd for 275yds at home and my bullets were going stratospheric, not coming down 'til almost 400yds out!

But man could I hit stuff!

LOL

I also found out that hitting stuff at 3-400yds with 6MM 105-107gr bullets it's kinda' hard to spot hits/kills. Those tough little javelins would just poke holes.

Now hitting stuff up close with 55's spinning 350,000 rpm's????? Stuff within 250yds???? ....HO'ley COW Batman.... talk about auditory feedback! It was like who flang the cat ag'inst the grain bin, spuh'LAKK!!!

I suh'WEAR, no feces, that the pieces of the species left the scope in a clockwise direction....



but that's another story entire....

al

 

[alinwa]

Never implied that the bullet's path curved, or that its path somehow converged.
Don't know what you are visualizing but it doesn't match what I said about overcoming initial yaw, or the effect of that temporary yaw on the short range group.
I won't bother going into it further.

Old Gunner,

in the interest of clarity to the folks reading this thread I need to point out that you and I are kind of mixing and matching terms and visualizations here..... and since we are, folks reading will get all sorts of confused impressions.

What I'M saying is that Magnus is only a factor in subsonic projectiles whose rotation is not aligned with the line of flight. A smoothbore musket comes to mind. I'm further saying that even though many older publications cite Magnus as having a measurable effect on high velocity projectiles, this has been shown to be incorrect. Also, that it's irrelevant to the concept of bullets showing decreased divergence as range increases. (I think you feel the same way re Magnus itself, but since you brought it up it gets linked to the divergence question...Same with Bernoulli.......)

Regarding the yaw thing (can we set The Italians aside for a bit?? ) I actually agree with you that it's THEORETICALLY possible for groups to converge as yaw damps.... but I'm further stating that it would be LUCK, like one out of ten or a hundred groups or something, because remember, the oscillation is 360 degrees..... for every time the group is WIDER than it should be, there's another time it's SMALLER because the "orbit" is inside the trajectory.

As I said earlier, I'm so into it that I wired my range with Cat5-R and a stick of 10-3 out to the 100yd butt. My intention is to set up an Oehler 45 such that EVERY SHOT is recorded through the acoustic target on it's way out to the 350yd butt. Over time this should give me at least on of these "converging groups" ...... if they're real.

meantime, I too have rifles which I can shoot better groups with further out, sometimes.

al

 

[Old Gunner]

but WARNING!! If you do work up loads in cold weather, with the powder cold, you WILL experience pressure excursions if you shoot those loads in warm weather. And although the term "pressure excursions" looks benign in print, in real life it means bad things.... like popped primers, busted triggers, even burnt face and eyeballs.....

The British found that out the hard way back when Cordite and other period Ng/Nc powders were first introduced to sporting rifle calibers in use in Africa and India. The cartridge manufacturers had worked up loads in Britian and Scotland at around 60 degrees at most, when these cartridges were used in 100+ degrees of the Indian sub continent or on the Sudan a good many fine rifles and shotguns turned into pipe bombs.
To a lesser extent .303 military rifles often required adjustment to or replacement of sights due to higher than expected velocities.

BTW
I remembered what you'd said about rolling in the air. Julian Hatcher used much the same term, and so did F W Mann. They went only so far as saying the air below the bullet was denser or thicker than the air above without going into the Bernoulle principle. In essence they were correct, they just didn't go into an extended explanation which the vast majority of their readers would not easily understand.

Also
I'm not exactly sure what you meant by

Skin and boundary layer effects are negligible to non existent for a supersonic projectile.

al

I find that hard to believe. If true then the F-102 fighter would never have maintained supersonic flight, its entire success being due to its boundary layer control through its coke bottle waist. Also controlability of supersonic aircraft would not have required the all flying tail.

According to Hatcher the deceleration effect of air resistence on a bullet moving at 2700 fps is 56 times that of gravity within the first few feet.
At supersonic speeds air is a fluid.

Speed does not reduce the effect of the atmosphere it greatly increases those effects.

the oscillation is 360 degrees..... for every time the group is WIDER than it should be, there's another time it's SMALLER because the "orbit" is inside the trajectory.

Apply side force X to the projectile and it deviates, further along its course apply exactly the same side force X in the opposite direction and its deviation is counteracted, but it is not pushed back into the same line of flight as before the first application of side force, its course is now parallel to its original course without further deviation from the same energy source since by now initial yaw has damped out.

 

[alinwa]

Old Gunner,

Hatcher was wrong

I have all his books as well as Mann and others... but all the modern ballistics text have to go out of their way to show (politely, because Julian S is THE Grand Old Man!) that while he was cutting edge for the day, he was uninformed.

Here's an easy way to picture it....

You shoot a bullet, it's got two "separate" motions, forward and downward. And every high school student learns that they're "independent of each other because a bullet DROPPED reaches the ground at the same time as a billet fired..."

KINDA' right, but not.

What this does is lead people to picture the bullet "falling through the air" at a rate of 32ft/sec/sec, it's easy to then picture this bullet falling FLAT, with it's nose still pointing where it started. It then follows that for this dropping motion it can "roll on the air."

But it doesn't.

It DOESN'T fall flat.

It noses over....

It then makes sense that from the bullet's perspective it NEVER gets wind on the side of it. (Which incidentally it can't anyways because it's going too bloody fast! IT HAS NO BOUNDARY LAYER present for Bernoulli to work with. The shock waves extend from the nose at too steep an angle.)

The "Angle of Repose" or "in flight yaw" or "Yaw of Repose" DO play a part in the drift of the bullet but not via Bernoulli or Magnus' effects. And this angle of yaw is dictated by what the bullet feels in the air. As the bullet "drops" through the air it feels a "wind" on it's "belly" and just noses over obediently in response to it. It it didn't it couldn't remain stable...... DOESN'T remain stable in extreme cases and tips over.

To the bullet, the wind on it's belly is no different than a side wind..... it just balances on what it feels.

(((OOOhhhhh this sort of description just pisses real ballisticians like Litz right off!!! )


Sorry Brian!





"Bullets SUCK ... and with a sidewind they suck sideways!"


(and as they fall thru the air they SUCK UPWARDS as well as sideways which is why wind drift has a vertical component, but I digress)


How did I get dragged into this, again?


LOL




al

 

[alinwa]

Apply side force X to the projectile and it deviates, further along its course apply exactly the same side force X in the opposite direction and its deviation is counteracted, but it is not pushed back into the same line of flight as before the first application of side force, its course is now parallel to its original course without further deviation from the same energy source since by now initial yaw has damped out.

This is absolutely, literally true. But I can't see how it helps your position!

you're restating my contention that only PART OF THE TIME can a bullet be "outside it's flight path" as it were....

al


ooops, edit...

It's NOT literally true that it returns to parallel, I read too quick. It actually hews CLOSER to it's actual flight path as it damps which means NOT parallel!

 

[Old Gunner]

However, free-flight spark tests have never been able to measure this force or moment; they produce such insignificant effects on the trajectory that even a high precision spark range facility cannot detect them.

Difficult but not impossible
http://www.google.com/url?sa=t&sour...rqXcDg&usg=AFQjCNEgTDMy89ioQnf-0oka4E_BF5SMhQ

A great deal of work is being done to minimize the magnus effect on supersonic projectiles of all sorts.
Unfortunately the work while available for review requires registering to research sites, and I doubt they'd look too kindly on citing it all over the net.

And no you can't kick a projectile back into its original course by applying the same amount of force which kicked it out of line to begin with.

But it doesn't.

It DOESN'T fall flat.

It noses over....

Not always. Tests of volley fire at extreme range showed bullets often struck flat or flipped and stabilized base first.
Tests of over spun 7.62 bullets have resulted in bullets stabilizing in a side on attitude at extreme range the barrel elevated at 38 degrees.

Elevation and vertical spread are functions of velocity and variation in velocity, osilation can't make the bullet strike higher or lower just by a change of attitude unless it scrubs off velocity in which case it would always strike lower.


The rolling in the air bit was to explain Bullet drill, the very measurable drift in direction of rifling twist due to the magnus effect. The long range ladder sights of military rifles were canted to compensate for this effect.
The .30-06 drifted to the right at a measurable and predictable rate up to a certain range then the drift reversed. I can look up the figures I saw them only recently.
Bullet drill is independent of crosswind, thats a different matter entirely.


BTW
The shockwave generated by the nose of a projectile doesn't insulate the body from aerodynamic effects, otherwise you would not see secondary shockwaves generated at crimping grooves.
The reason supersonic aircraft require the all flying tail is because secondary shockwaves forming at the interface of horizontal stabilizer and elevator would lock up the elevator.

 

[shootsteady]

DOESN'T remain stable in extreme cases and tips over....

How does hollow points fit into this equation?

 

[alinwa]

Difficult but not impossible
http://www.google.com/url?sa=t&sour...rqXcDg&usg=AFQjCNEgTDMy89ioQnf-0oka4E_BF5SMhQ

Solid cite but I'm having trouble finding anything that doesn't support my position. This article explores whether or not more study should be done and concludes that NO, there's no need. It shows that boundary layer effects are meaningless.

I certainly don't see "a great deal of work being done" re Magnus, your cite seems to me to be saying the opposite, it states that there's no real reason to explore further (which had been established for 20 yrs...)

f'rinstance,

quote- "2. The computational show the relative effect between
smooth and grooved (rifled) projectiles to be minimal
over a range of spin rates and that the rifling grooves do
not produce aerodynamic effects responsible for the
observed trim angles.."


So, I guess we still disagree.

al

 

[alinwa]

The rolling in the air bit was to explain Bullet drill, the very measurable drift in direction of rifling twist due to the magnus effect. The long range ladder sights of military rifles were canted to compensate for this effect.
The .30-06 drifted to the right at a measurable and predictable rate up to a certain range then the drift reversed. I can look up the figures I saw them only recently.
Bullet drill is independent of crosswind, thats a different matter entirely.

.

WRONGagain......




I just couldn't include this in the other reply.......

Here you've made your position clear. You're using a term, "Bullet Drill," which is completely dialectic and imprecise but I'll go with it. The actual term is "Gyroscopic Drift," commonly called "spin drift" and yes of course it's real and easily measured and accounted for....

And it's NOT CAUSED BY MAGNUS!!!

Jeepers, this idea is from the 1800's, it's OLD and it's simply not true. Gyroscopic or spin drift is a DRAG EFFECT and contrary to your statement it is NOT independent of crosswind. Any Bench Rest shooter knows that bullets hit HIGH in a Right-to-Left wind and LOW in a L-to-R

This too is due to gyroscopic drift. (Or as you call it bullet drill)

NO, bullets do not roll on the wind, they haven't in this century.

And NO, the cause of ("bullet drill," "Spin drift," or "gyroscopic drift") IS NOT MAGNUS!

And no your cite on a tax dollar funded "study" of the Magnus effect doesn't prove your point.


Drag, drag, DRAG..... it's about DRAG, not about "rolling on the air." There is no such animal as rolling on the air..... regardless every jarhead in the corps learns it.....

The fact that everyone learns it this way doesn't make it right. Tradition always trumps truth, it's hard to buck an established tradition that's been passed on for decades to thousands of ignorant young men.

My kid is in Afghanistan as we speak, he learned the hard way that you don't bring this stuff up to Gunny!!! Gunny asked the class "does anyone understand wind drift?"

And he was stupid enough to raise his hand and say "yes."

The Corps has taught him though, shut up and move on....... it ain't ABOUT truth, it's about what gets the job done.

sad but true


al


Ohhh, and another thing before I shut up

The drift does not reverse at distance...... Drag induced drift does not reverse itself. It just IS. Saying it reverses is like saying that "some time ago the earth reversed rotation which caused the magnetic poles to flip which extinctified the dinosars which caused the rise of mammals".....or something. Not only is it conjecture, it's WRONG-headed conjecture based on a poor understanding of basic physics.

Nor would "Magnus Effect" reverse itself, unless the bullet stopped rotating and started in the other direction!

think about it


alagain

 

[Old Gunner]

You're pitting your theory against effects proven by ordnance departments expending millions of rounds in testing at ranges you are unlikely to ever attempt to shoot at any target.

The reversal of direction of drift at extreme range of the .30-06 as fired from the 1903 rifle with 1:10 twist due to bullet drill was measured and confirmed and only the magnus effect could account for that since its known to reverse as a projectile drops from supersonic to transonic and subsonic velocities.

Bullet Drill (yes thats a very old term still in use) is independent of wind because the drift is there in still air, cross winds can increase or decrease the amount of drift but the side force of the drift due to bullet drill is stil there cooperaing with wind moving in the same direction as the rifling and combating wind thats moves in opposition to direction of rifling.
By adding cross wind to the mix you are introducing a new energy source which is not a function of bullet drill itself.

Testing of .50 ammunition

We shot 18000 rounds of 50 cal ammo during
a contract. The guns were sighted in and function tested at 100 yards
and averaged 1.5 moa groups. When these same guns were tested at 600
yards you would expect the groups to run 1.5 moa or 9 inches. The 600
yard targets ran as small as 3 inches and never any larger than 6 inches
as an average. Any that shot larger than 9 inches were inspected and re
tested.

Gale McMillan

http://www.google.com/url?sa=t&sour...hPmnDg&usg=AFQjCNEIWq69GYr_k9e3ryVKN8O1qgEevQ


The nutation of the point of the projectile is an ever decreasing spiral, but does not result in a spiral path of the bullet in flight, if it did the decreasing spiral would result in groups at 200 being smaller in inches center to center than groups at 100 rather than smaller in MOA..
Any deflection in fractions of an inch introduced within the first few yards due to variations in effects at the crown due to bullet base excessive muzzle blast etc remain. As the bullet settles down those transitory deflections are no longer a factor and don't result in further deflection as the nutation decreases presenting the bullet at its optimum attitude as range increases.

BTW
Among the recent developments in decreasing the magnus effect are surface finishes of bullet jackets intended for long range sniping.
The surface finish breaks up the boundary layer effects which you don't seem to believe can exist on a supersonic projectile.

 

[Old Gunner]

Al said

Solid cite but I'm having trouble finding anything that doesn't support my position. This article explores whether or not more study should be done and concludes that NO, there's no need. It shows that boundary layer effects are meaningless.

They wouldn't be trying to reduce the magnus effect if it was of no concern.
They found that the differences in the measurable effect on a 5.56 bullet with rifling engraved compared to a pristine bullet when both were fired by means of a sabot did not warrant further study, the reduction in the effect was not worth the effort of developing a sabot .223 bullet for small arms.

I'll let you guys debate the scientific principles, I'm just happy to know that the Litz book provides useful, practical information. As a matter of day to day results, my group size always gets bigger with more distance and I find about a 3 moa drift to the right at 1000 yd. compared to a 600 yard zero with a .308 or .30-06 (just to touch on two of the points of debate).

In Farrow's "Manual of Military Training" on page 306 he gives the short form description of the reversed drift of the .30-06 ball with the bullet first moving to the left of the bore line, which he states as "uncorrected line of sight" up until 500 yards where it crosses the boreline and proceeds to take up the normal expected right hand drift.

So I had mis stated when I wrote

The .30-06 drifted to the right at a measurable and predictable rate up to a certain range then the drift reversed. I can look up the figures I saw them only recently.

My Enfields all have left hand twist so I'm more used to a lefthand drift.

I had typed this out earlier but somehow deleted the post so I'll just provide a link to download the book.
http://books.google.com/books?id=Va...ook_result&ct=result&resnum=1&ved=0CBYQ6AEwAA

I think theres a better description of drift reversal in an ordnance publication, I'll look for it.

I could be wrong but I suspect a shift in the position of the magnus moment in relation to center of pressure or center of gravity would be neccesary for the early lefthand drift and its down range reversal to the expected right hand drift.

 

[Donald]

Don't you just love it when two gentlemen with a great deal of knowledge about our sport discuss their differences in a civilized manner. Makes for a very interesting read. At this point I would rate "al" as slightly in the front. Go for it guys.......

Donald

 

[Old Gunner]

Well I may be off the beam on a few points but heres the quote on the lefthand lateral jump of the 06.
Same wording as in Farrow's Manual but from a National Service publication.

The rifle has a right-hand twist, and the drift proper is therefore to the right. There is, however, a slight lateral jump to the left, and the total horizontal deviation of the bullet, excluding wind, is the algebraic sum of the drift and the lateral jump. The trajectory is found to be very slightly to the left of the central or uncorrected line of sight up to a range of 500 yards, and beyond that range to the right of this line. In order to minimize the deviations at the most important ranges, the drift slot on the sight leaf is so cut as to make the trajectory* cross the adjusted line of sight at a range of 500 yards.

Could be a mechanical effect rather than aerodynamic effect.

I don't believe so much research would be underway to reduce the magnus effect on bullets if it were of no consequence.
The military is interested in bullet performance far beyond the ranges that any marksman could hope to score on a individual target.
The performance of a bullet beyond the 1200 yards line of a rifle range would be of little importance to a target shooter, but since rifle caliber MGs can deliver indirect fire out to 4,500-5,000 yards or so and volley fire at ranges of well over 2,000 yards was still in use as late as early WW1 the performance of bullets at such extreme ranges makes even supposedly tiny effects something that requires consideration.

The impressed surface finish of some experimental ultra long range sniper bullets is directed at reducing the magnus effect.
Sabot high velocity AP rounds are already in use, the experiments on a sabot 5.56 may not have proven to be much if any improvement over engraved bullets but the effect and its reduction were measurable.

The Poisson effect related to the Magnus effect ordinarily would acentuate the Spin Drift but can counter spin drift if the nose drops. There doesn't seem to be any hard information on this.

PS
Remember this Al?

It then makes sense that from the bullet's perspective it NEVER gets wind on the side of it. (Which incidentally it can't anyways because it's going too bloody fast! IT HAS NO BOUNDARY LAYER present for Bernoulli to work with. The shock waves extend from the nose at too steep an angle.)

We consulted some of the top civilian bullet experts, including ballistician Bryan Litz of Berger Bullets. Mr. Litz really got the ball rolling. He suggested that the ‘next big step’ in bullet design would involve the turbulent boundary layer over the body of the bullet. Litz told us that ‘pointing bullet tips will take you only so far… think about optimizing the airflow over the entire bullet’. That made a lot of sense to us. When you design a race car to be aerodynamic, you sculpt the whole body, not just the front bumper.”

Lt. Col. Eldrick continued: “It turns out Litz was right on the money. By employing a golf-ball type dimpled surface, we were able to optimize the turbulent boundary layer on the bullet body. This reduced the low-pressure wake zone behind the bullet significantly, resulting in reduced base drag. As a result the bullet experiences much less overall drag, effectively raising the BC.” The Army team had discovered that what works for golf balls also works for bullets.

So boundary layer effects are not inconsequential.

http://www.google.com/url?sa=t&sour...m6HKCw&usg=AFQjCNHZrgPcGwRqH70I6gRRKs5pdQ1nrA

 

[alinwa]

Now we're getting seriously sideways.... As I said, we're in an area which isn't adequately served with info available in a Goog-search.

Brian and I disagree on this

In fact I think Brian's totally out to lunch on this one! And it certainly won't be the first time we've argued here on BRC if he takes me to task for it. But remember, this is all THEORETICAL..... If Brian believes in dimples and gets Berger to try it AND IT WORKS I'll happily and publicly eat crow. But Brian has learned he has to prove his view here...

Meantime I think he's jousting at windmills.

And BTW I've got some absolutely needle-pointed handmade projectiles here that Henry Childs made up which show that not only can "only so much be accomplished via tipping".... but that tipping itself has limits. HBC shows how needles aren't good either.

You really need to understand the term 'lateral jump' before throwing it out there, as well as Poisson's.... Both are irrelevant to your argument, and I'll clarify that anything I've said applies to supersonic flight only, transsonic or subsonic effects need not apply. Nothing in the accuracy game includes bullets dropping through the floor. (Also exempt are rimfire and whisper-work and other truly subsonic stuff which are DESIGNED this way right off the muzzle.... and another subject entirely... and also NOT dropping through)

BTW lateral jump occurs at the muzzle.






al

 

[Old Gunner]

Brian and I disagree on this

In fact I think Brian's totally out to lunch on this one! And it certainly won't be the first time we've argued here on BRC if he takes me to task for it. But remember, this is all THEORETICAL..... If Brian believes in dimples and gets Berger to try it AND IT WORKS I'll happily and publicly eat crow. But Brian has learned he has to prove his view here...

Meantime I think he's jousting at windmills.

Lt. Col. Eldrick continued: “It turns out Litz was right on the money. By employing a golf-ball type dimpled surface, we were able to optimize the turbulent boundary layer on the bullet body. This reduced the low-pressure wake zone behind the bullet significantly, resulting in reduced base drag. As a result the bullet experiences much less overall drag, effectively raising the BC.

Sounds like you are saying Lt Col Eldrick is full of beans, the bullets obviously do what they were designed to do.

As for the lateral jump, no explanation for this was given , so perhaps I was extrapolating, in part because I'd let my own lefthand rifled rifles intrude on my thoughts on this. The subject was one I had not taken much noticed of when I first ran across it. But the reversal of the Magnus effect when the nose is in a down attitude and the interaction of the poisson effect is a possibility. With the subject of bullets nosing over at peak of trajectory having been mentioned earlier then reversal after peaking is a strong possibilty.

But as it stands neither of us is 100% right, and your errors are basic with no apparent understanding of boundary layer effects or even recognition that they exist.

Litz is not the only one using surface finishes to reduce boundary layer and the magnus effect, the Chinese military are also working on this, their treatise on the subject is not available without registering to a research journal site though.

And of course the lateral jump happened at the muzzle, one of a number of transitory effects overcome by the increasing stabilization of the bullet as it goes to sleep as some put it.
The reversal due to lateral jump is negated by the 500 yard mark after which drift is to the right as it should be.

So our discussion has been fruitful in a number of ways.
While your insistence that shockwaves somehow insulate the body of a projectile from boundary layer effects appears to have been proven false by actual measured effects of real bullets tested by the army.
Your contention that the magnus effect could not be observed and measured by spark photography was also proven false.

Main difference is that when I found I'd misread and mistated I corrected, you on the otherhand ignore published results if they don't match your preconcieved notions.

You may have a point mixed in with your misinformation, but if so its been obscured.

You might start by proving that theres no such thing as the poisson effect. Not that it can't be demonstrated as you thought the magnus effect could not be, but proof that the theory doesn't hold water.

 

[Greg Culpepper]

The dimpled "golf ball" surface was an April Fool's joke on www.accurateshooter.com . It was a bit too plausible and people began to believe it. A number of other websites even began to report it as true. "Eldrick" is Tiger Woods' first name so it was used for the fictional colonel. Sorry about that...

http://bulletin.accurateshooter.com/2009/04/dimpled-bullet-spoof-continues-to-fool-web-readers/

Never spoil a good story with the truth! I wonder how long some will cite this gem to support the unsupportable.

 

[Old Gunner]

Well jokes on me on that one, but that doesn't alter the fact that the same sort of experiments in reducing magnus effect are being explored by actual government institutions.
I can look up the links to the research papers on these, there are a slew of them and none april fool related..

 

[Old Gunner]

Never spoil a good story with the truth! I wonder how long some will cite this gem to support the unsupportable.

Is this also an april fools joke???
http://www.google.com/url?sa=t&sour...rqXcDg&usg=AFQjCNEgTDMy89ioQnf-0oka4E_BF5SMhQ


Just to be clear, how many here believe that theres no boundary layer effect on a supersonic projectile?

 

[alinwa]

Gunnner, I have the utmost respect for the work done at Aberdeen but don't begin to have the necessary background to understand it or most scientific analysis of these issues. That's why I stay out of these discussions. My testing, which was as straighforward as I can make it, was an attempt to follow the logic in Litz's book with some actual firing and I found that my firing results were supportive of his work and predictions. That's as far as I go on the subject - I'm no scientist.

See, German's problem is...... he spends entirely too much time actually SHOOTING.

I keep telling him: "German, you're wasting time here, get'cher butt back inside and GOOGLE this stuff. Shooting and testing stuff is just so, so..... well, serious and time consuming!

"You ain't got sense to come in out of the rain...."

But he doesn't lissen A'tall.

Maybe someday he'll wake up and smell the coffee.....

speakin' of coffee....

ahhhhh


al

 

[alinwa]

DOESN'T remain stable in extreme cases and tips over....

How does hollow points fit into this equation?

All Match Grade bullets are hollow points for two large (and several small) reasons.

#1, only by leaving the point empty can proper weight distribution be achieved. CG MUST be held to the rear for a bullet to behave properly. If you bring the center of gravity too far forward you run into oscillation problems. To understand this look at a child's top. A top is fat on top. Make a top fat on the bottom or spin it upside down to see why. A stable bullet is a 'top' which balances on the airflow it perceives...... bring a wind in from the right and the top "rights itself" by nutating over to 'balance' on the new vector. A proper bullet must be light in front.

#2, mechanically the front should be left empty for mfg reasons.... pointing up a bullet with a nose full of lead leads to unpredictable, uncontrollable eccentricity. This is huge. This is one of the reason full-core bullets (Game Kings, Silver Tips, Partitions to name a few) can never be accurate.... and partial hollow points can be even more problematical. Read 'Rifle Accuracy Facts' section on .270 bullets to see with pictures and descriptions how unsupported lead will slump, yet understand that while lead is "fluid" under pressure of firing it's still a very viscous fluid and therefor cannot redistribute itself for balance. Hand made Match Grade projectile as recently detailed in the 50,000 views (defunct??) bullet making thread will always be hollow points. As will machine produced bullets.... just go to Sierra's site to see that Match Kings are the hollow pointed projectiles on the page.

Other problems have to do with flexure during flight and several other mfg details..... as well as the fact that when using fragile J/4 jackets the pleats are likely to open and spew molten lead if you get it up into the point section very far.

BTW a tipped bullet like NBt or A-Max is still a hollow point, but with the point plugged with a hunk of plastic or AL or somesuch, not necessarily a good idea.


hth


al