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Your pointy bullets and their flight

Bryan -

Jerry's question above is a good one, that I would like to hear your input/opinion as well...

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Back to core height: and maybe I am not understanding the total package and profile of the column bullet correctly. So I'll scratch calling what I'm am talking about, column bullet philosophy, and just go with what I have seen prove out on target accuracy. And that be: core height.

Say we don't care what the bullet weights end up at, only being concerned with the height of the core and the amount of "void" above it. Do you feel controlling the height of the core and a set amount of "void" space, more so then the density of the lead core to hold a weight specification would have relevance to accuracy potential of a bullet like I seen prove out?

While I can understand the need to hold a weight specification and a consistent BC for marketing purposes in general. Those type aspects are the least of my concerns for LR competition target shooting. Single-Lot consistency and RAW accuracy capability rules all else in our realms, sort to speak....

Donovan
 
Jerry,

We have to clarify some definitions here.

When referring to bullets, static balance is not front to rear, but radial. It's an offset of the center of gravity from the center axis of the bullet. Static imbalance is typically introduced in bullets from jacket eccentricity (jacket is thicker on one side than the other, thereby causing the core to be off-center). This is why jackets with low run-out are so critical to precision. A small amount of static imbalance (0.0001") will make it impossible to shoot BR winning groups. Dispersion from static imbalance is related to twist rate, which is why many BR shooters choose the slowest twist possible.
A football has static imbalance due to the weight of the laces on one side.

Dynamic imbalance is harder to explain/envision. In engineering terms, we say that bullets have a geometric axis (simply the line defined by the bullets shape) as well as a principle axis of inertia which is determined by the mass distribution within the bullet. These two axis are the same if the bullet is perfectly balanced. If these two axis are not parallel, the bullet has 'dynamic imbalance'. If the two axis are parallel but not together, then the bullet has static imbalance.
Back to football, when you see a ball thrown that is 'wobbly', that perceived 'wobbly-ness' is what dynamic imbalance looks like. Note this analogy isn't strictly accurate, because the ball itself isn't dynamically unbalanced, it just wobbles because of being thrown imperfectly.
You could introduce a dynamic imbalance to a bullet by drilling a 0.030" deep hole (for example) 1/4" behind the CG on the left side of a bullet, and another hole of equal depth 1/4" ahead of the CG on the right side. This wouldn't necessarily ruin the static imbalance of the bullet, but would introduce a dynamic imbalance.

It is possible for a bullet to have purely static imbalance, or purely dynamic imbalance. In reality, every bullet has some amount of both, even if it's not measurable (because nothing man-made is 'perfect')

Static imbalance is the big enemy of precision. When the bullet is in the barrel, it's confined to spin around it's geometric axis. But when it emerges from the confines of the muzzle, it immediately begins spinning around it's principle axis of inertia (CG) (because it's now in free-flight). For a bullet having no static imbalance, it will come out of the barrel and fly straight. But if there is static imbalance, the bullet will gain some lateral velocity as it exits the muzzle.

Your question referred to static imbalance being related to the fore-aft position of the CG, which, for a bullet spinning on it's proper (long) axis, wouldn't have an effect on balance.

The fore-aft location of the CG does affect the bullets *stability*, which is entirely different from balance. A bullet can be stable and un-balanced. It's also possible for a bullet to be balanced and unstable.

Balance is a property of the bullet itself. Stability is determined/affected by it's spin rate, velocity, air density, as well as it's mass and aerodynamic properties.

On the subject of precision, stability has very little effect until you fall below the critical stability factor where the bullets don't fly point on and start key-holing on target. Even keyholing bullets can be relatively precise. I shot a 300 yard group with 300 grain solids from a .338 LM, 1:10" twist which printed ~1" long keyholes and the group was under 1 MOA. This is not typical or desirable, but just shows that stability and precision aren't necessarily linked.

For stability levels below 1.5, you can measure a decrease in the bullets effective BC due to the bullet flying with greater pitching/yawing angles, but again, groups don't suffer from this marginal stability. In fact, if you're dealing with bullets that have a great deal of static imbalance, you can expect *better* groups from marginally stabilized bullets because the slower spin rate results in less dispersion from the same static imbalance. Again, consider the tendency of short range BR shooters to choose slow twist barrels. Typically, stability factors of short range BR shooters are in the 1.1 range and it's not uncommon to see minor key-holing if conditions (air density, MV) are not favorable to stability on any given day.

Donovan,
To your questions about core height, I'll attempt an explanation, but admit I may be going out on a limb. I welcome comments from someone with more hands on experience actually 'making' bullets to comment on my statements here.

The question: Might it be favorable to go for a given core height vs. overall bullet weight when dealing with different lots of raw materials.

I *think* this may have to do with the array of tools available to the bullet maker; in particular core seating punches. Since jackets are tapered, and will vary in their thickness vs. height from lot-to-lot, the bullet maker is compelled to use different diameter core seat punches for different lots of material if he wishes to achieve the proper fit to jacket *and* make all lots of bullets the same weight.

For example, if a bullet maker only has one core seating punch, he may have to make the cores longer or shorter in order to achieve the proper fit to jacket and core seating pressure with any given lot of components. As you described, this would result in bullets of slightly different weight.

However, if a bullet maker has many core seating punches graduated in 0.0001" increments, he can accommodate the range of raw materials, and properly seat a core to any length necessary to achieve the desired weight.

The core seating punches used by Sierra for their MatchKing line of bullets has a clever feature. The face of the core seating punch is hollowed out, which allows the lead to relieve up into the cavity as much as it has to. This way they can use the same core seat punch on many different lots of lead and jackets, and there is someplace for the 'remainder' to go. Another function served by this cavity is that it acts to relieve and equalize the pressure on each stroke of the machine. For machines like those used by Sierra in which several forming operations are performed on each stroke, it's important that the energy of each stroke is equally distributed.

Berger's presses are single stage, meaning that the energy from each stroke is used on one forming operation at a time. The correct core seating punch is selected for the given lot of materials such that everything 'fits', and results in bullets of the desired weight.

Both process can make good bullets. In the end, the single biggest thing affecting precision is the jacket run-out. Over the years, Berger has been able to maintain a reputation for high precision. This has been achieved primarily thru a strict commitment to using jackets with 0.0003" run-out or less (which makes bullets balanced to within 0.0001"). Other advancements in bullet making have been made related to manufacture-ability, and lot-to-lot consistency. But the biggest thing in precision bullets remains static balance, and it all starts with concentric jackets.

Jackets with 0.0003" run-out or less has set Berger Bullets apart from others since the beginning. Walt Berger shot is way into the BR Hall of Fame with bullets that were made on jackets that he turned on a jewlers lathe, one at a time, so they had less run-out than any other bullets. Eventually J4 started mass producing the high precision jackets, and Berger has used them ever since.

I'll let Eric Stecker know about this thread and see if he's able to address any of my comments on core seating punches.

Take care,
-Bryan
 
All Commercially made bullets of a said specific weight, of the same lot # do not weigh the same. doesn't matter the maker Berger, Hornady or Sierra. I have weight sorted them they usually have about 12 different weights within 1 lot.

That makes me believe that all of those bullets in that specific lot, of lets say 105gr bullets, do not have the same core height because if they did they should all weigh the same at 105 grains. Now if they all had the same core height they would all be the same weight regardless if it was exactly 105 or 104.96 or 105.08. if they all weighed the same with the same core height they would be more uniform and should be more accurate. I have seen people change lots and all of a sudden their rifle won't shoot maybe that is why, the core height changed and their barrel does not like that.

I have to believe that if someone took the time they could figure out an exact core height for a given bullet shape that regardless of weight, it would make it shoot more accurately and keep that core height from lot to lot and just let the bullet weight change also from lot to lot.
 
Regarding core seating punches and core column heights, this is a subject on which I could spend a lot of time writing a lot of information that few would find interesting or useable. I will confirm that we fit our seating punches to each lot of jackets.

Jacket weights within a given lot typically are tight because they have tight dimensional controls. In drawing and ironing, the copper can only go where the tools put it. It is rare to see jackets that weighs more than +/- .05 of a grain. I could be wrong but given how jacket forming is done I would expect this to be true of any brand as long as they have good tooling and lot controls

Even jackets with "higher" TIR should weigh the same or similar. The part of the jacket that is thicker is typically on the same side every time so the weight should be the same. The difference in the weight of the finished bullets comes mostly from the differences in the amount of lead.

Controlling the weight of the cores is far more challenging. If you simply feed and cut your cores from wire the weight will vary considerably due to differences in diameter and feed mechanisms. We use a swagging process to form our cores into a single die to get uniform weights. I won't go too deeply into how we do this but our goal is to maintain tight weight controls on our cores.

It is true that if you have a bullet that is too light or too heavy, the forming forces can be different if you don't compensate for the fact that the volume in which you are forming the bullet is fixed. This can affect dimensional consistency. One approach to overcome this is to relieve the punch to allow for the lead to flow into a cavity in case there are variations in the weight of the cores. if you cut a bullet in half you can quickly see which brands use this method.

Our approach is to keep tight control of our core weights so that we can use flat, fitted punches. This is what Walt found to make the most consistent bullets.

Why one lot of bullets performs differently than another is a puzzle that we are eager to solve. Our approach is to make bullets that are as consistent as possible. Consistency at least helps reduce the variability in working to achieve top performance.

The trick is, at what combination does that consistency pair up with the tune of a given rifle. Once you have both consistency in the components you use and proper tune the results should be exceptional.

I suspect that whomever sorts out the quickest way to get there will do very well until the rest of use figure out how they've done it.

Regards,
Eric
 
Wow, this was very informative. I did run a test on some Berger 180 hybrids when they first came out. I first weighed and tipped them. I took the culls-various weights- but all outside of .5 grns weight and shot the heavy and light alternately at 1000 yrds on an exceptionally calm morning at Lodi. Took me three weeks to get a day like that.

They both shot two mall groups around 2.5 inches. One centers at the x and one centered on the 9-10 ring. Oddly the heavy ones shot higher! Not sure why. Guess they built up a little more pressure. I just got done weighing 1000 6mm 105's and 1000 180 gr 7mm hybrids on Christmas day. Fun times! Anyway I was amazed at how close in weight they are now.

I have been trying to make my own bullets-going on 4 years now, still waiting for some dies. I think I will not be able to produce any better bullets than Berger or some of the custom guys and I probably wasted a bunch of money!
 
Bryan and Eric, thanks a bunch. Lots of shooters will benefit from what you guys are telling us. (I'e missed out for some reason I don't have my 6mmbr account set up so it notifies me of replies).

Getting back to the original intent of this thread, which I intended to get some feelings (explanations) of how or why bullets that have a longer unsupported portion of their body may be harder to get to shoot accurately because, for a simple explanation, may have more wobble going down the barrel or at least have more wobble in the earlier part of their flight. I am using the word wobble for what is technically called yaw.

Now, if we can use technical terms, lets try to explain the inconsistencies of the bullet in its flight using ANSI/GD&T Y14.5 terms. These standards for dimensioning and tolerancing gives us more finite definitions to use, for example circularity and cylindricity for controls for the simple circle.

http://en.wikipedia.org/wiki/Geometric_dimensioning_and_tolerancing

I hope I'm not pushing my asking too far. If so, I apologize.

.
 
Getting a little deeper in trying to set up and control the important parameters of a physical object, in this case our bullet:

"GD&T representation: Unlike GD&T presentation, the GD&T representation does not deal with how the information is presented to the user but only deals with which element of a shape of a product has which GD&T characteristic. A system supporting GD&T representation may display the GD&T information in some tree and other dialogs and allow the user to directly select and highlight the corresponding feature on the shape of the product, 2D and 3D.
Ideally both GD&T presentation and representation are available in the exchange file and are associated with each other. Then a receiving system can allow a user to select a GD&T callout and get the corresponding feature highlighted on the shape of the product.
"
 
Bryan and Eric, Some of this is so deep that that it's like tripping over 20 dollar bills to pick up a penny. I have and had issues with the dimensions of the pressure ring getting huge on the 105 bullets ……… why? They get to the point that they are so much larger than the shank that spring back in the neck won't hold the bullet except for the small area at the pressure ring and it is starting to show up in a number of bullet makers. Nobody seems to have the answer why a diameter at the pressure ring can change but the shank size stays the same. Does it grow after it comes out of the die? Why doesn't the shank grow at the same rate? …….. jim
 
raythemanroe said:
Maybe try a twist on the BT to stabilize flight like an arrow fletching Jerry?





Ray

Ray, I have a strong feeling the BT is not the problem, the crown might contribute if it is not symmetrical however. But, if the bullet is traveling down the barrel with ANY yaw it probably will not be as consistently accurate as a bullet minus ANY in-bore yaw.

If the bullet can exit the barrel asleep it SHOULD be more accurate than a bullet that takes a portion of its flight to fully stabilize. I.e. I don't think bullets get closer in flight??
 
Hey Jerry, Piedmont is having a "fun" match this Saturday. Gather up your stuff and go by and get Carmichael and come down and shoot with us. It has been a long time and we miss you.

Larry Isenhour
 
I'd love to Larry but Saturday is already spoken for...family stuff.

Hope to see you at the Hickory Egg Shoot and at Unaka. I'm going to try to do SOME 600 again this year.

I did a couple of 6BR barrels and they don't shoot the pointy things worth crap. I probably will go back to my 6-40 Dune and Berger 90 grain BT's . Lester had some 1000 round boxes and I got a couple that I haven't opened. I do have a 6-40 barrel screwed on my LG finally.

That is why I started this thread. I can get the old Berger LTB's and these 90 BT's to do better and they both have less pointed noses.
 
Jerry, hope you do get to shoot some 600yd this year. It is still fun for me because I get to spend time with my son Paul and James Coffey. James rides with me to the match and at 82 he is very competitive.

This has been a good discussion. You have cured some "winter time blues" by getting this started. I am not winning much anymore so I am the last person you should listen to for advice. Rodney and Sam and Mike Haines will share their thoughts with you. They are at the top of the game right now and would be the ones to listen too.

And another thing Jerry, You have been doing this for a long time so I suspect you aren't far from where you need to be. It is always good to get thoughts from others just to keep us from getting "tunnel vision".

Happy New Year. I have enjoyed this thread.

Larry
 
jerrysharrett said:
I'd love to Larry but Saturday is already spoken for...family stuff.

Hope to see you at the Hickory Egg Shoot and at Unaka. I'm going to try to do SOME 600 again this year.

;)I did a couple of 6BR barrels and they don't shoot the pointy things worth crap. I probably will go back to my 6-40 Dune and Berger 90 graBT's . Lester had some 1000 round boxes and I got a couple that I haven't opened. I do have a 6in-40 barrel screwed on my LG finally.

That is why I started this thread. I can get the old Berger LTB's and these 90 BT's to do better and they both have less pointed noses.


I thought you told me you could make the VLD's shoot…….. i really don't think it's the bullets, but it could be try some Vaper trail bullets……. jim
 
I can make them shoot Jim. I just don't like the long pointy things and I don't like the 6BR. For shooting in 600 yard competition there are much better choices than VLD's and 6 BR's.
 
jerrysharrett said:
I can make them shoot Jim. I just don't like the long pointy things and I don't like the 6BR. For shooting in 600 yard competition there are much better choices than VLD's and 6 BR's.


If it isn't shooting in a .1 or less at 100 yds. your right it isn't shooting…….. If you haven't tried the Vaper trails do so and if they don't shoot go to the BIB104 it isn't a VLD and it will if you have a 8 twist barrel. if both don't work it could be your scope or gun. If all of those are good it your loading, what worked for short range will not begin to work for long. I have done both and short range methods are too crude to be successful at longer ranges. Either bullet is as perfect as any short range bullet…… including the jackets……. jim
 

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