Meplat closing, and coherence among ballistics programs

C

Charles E

curmudgeon
Background:

On another thread on the topic of repointing bullets (AKA meplat closing), Jim Hardy made reference to a test by Jason Baney, firing 106 Clinch River 6mms at 1,000 yards. The repointed bullets were, I believe, done with the Whidden die, not Jim's Pindell system. The bullet strike with the repointed bullets was reported as 18 inches higher than the "as issued" bullets.

I began to wonder if this number fit with the predictions made by several ballistics programs. Damon cautioned us that the current programs are not that refined. Still, there should be a general agreement.

Not only the programs fail to be terribly precise. We've all been at matches where we were zeroed up pretty good in the sighter period, but seen our record group, fired about 10 seconds after the last allowed sighter and taking as little as 20 seconds to complete, print around 10 inches low. Still, let's just use 18 inches as the best number we have.

What would the change in BC need to be to give a group 18 inches higher? The numbers I used were a MV of 2950, and G-1 BC of .520.

This gave the following on the Pejsa program: Bullet falls 290 inches, with a time of flight of 1.50 seconds, and a 10-mph crosswind deflection of 85.4 inches.

Changing the BC to .567 resulted in a bullet fall of 272 inches -- 18 inches less than the stock bullet. TOF was 1.44 seconds, with a 10-mph crosswind deflection of 75-inches.

So, that's a .047 increase in BC to get those numbers. Is that reasonable? We didn't have the numbers from Greg's bullet for the JBM program, (106 CR), but R.G. Robinett has the exact numbers for his 108 BT, which is similar

This is what he reported:
. . . hypothetically, this - decreasing the meplat diameter from 0.05, to 0.01' - would increase the CALCULATED BC (real-world is always less) of the 108 BIB BT by about 0.040: from 0.542 to 0.583. . . .

. . . for those who don't know me, I don't make this stuff up - these calculations are from the Tioga Engineering (the late Bill Davis) program, which, used in conjunction with the McCoy based programs at JBM BALLISTICS, has resulted in some decent real-world results. The Tioga and McCoy results are always very close . . . well, unless I enter bad data! A 0.010" knock-out pin would need some SPINE!
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Well, it is in the ballpark, but maybe not reasonable. I doubt Jim could close the meplats to .010 with just the Whidden die. And Randy points out the real-word numbers are always a bit less, though in this case, the needed INCREASE would likely be very close. The real-word "lesses" would be the numbers themselves.

* * *

Another interesting thought. I shot the 106-CR for over a year in a 6mm Ackley, with an initial MV a bit over 3,200 fps. What's that give? Same BC of course, but a bullet drop of 236 inches and a TOF of 1.36 seconds. Significantly "better" than the repointed 106, except for a kicker: the 10-mph crosswind deflection of 74.7-inches is about the same as the repointed 2,950 MV bullet. Even though TOF was 0.08 seconds less, drift was the same as the higher BC bullet.

* * *

OK. ceteris paribus, repointing bullets should always show a significant advantage. The one (of several) test I made where it did not is now suspect. It needs to be repeated.

Secondly, picking up BC by repointing is more effective than lowering TOF by increasing the initial MV -- no surprise here, score shooters have always known & preached that.

Certainly we need more data. Anybody got a 1,000 yard tunnel?

I, for one, do not know the potential downsides. How hard is it to muck up repointing so there is dispersion in the group? No idea.

Secondly, more than meplat diameter alone is probably be at play here -- Nose shape is probably a factor. And with that, can we make a repoint die where it is fairly easy (cheap) to use a different radius? Can we have, say, a 15-caliber secant ogive for the nose? Since the optimum nose shape will vary with the mach number, is there a way to design the tool to accommodate the different nose shapes? Is that what the Hoover systems provides for?

And if so, will we need bullets optimally pointed to use it? Bullets with the lead not going so far up the bullet -- for example, a 187 BIB on an 1.4 jacket rather than it's standard 1.3 jacket. Can we repoint these better, in terms of nose shape?

Does Bryan Litz already have a program where we can plug in the desired mach number to determine the best point shape?

Etc.

Charles
 
Charles E said:
Background:

On another thread on the topic of repointing bullets (AKA meplat closing), Jim Hardy made reference to a test by Jason Baney, firing 106 Clinch River 6mms at 1,000 yards. The repointed bullets were, I believe, done with the Whidden die, not Jim's Pindell system. The bullet strike with the repointed bullets was reported as 18 inches higher than the "as issued" bullets.
Click to expand...
Charles,

Unless the test was done via alternating shots, the resulting data could easily be skewed some. Was the rifle cleaned between, was it not cleaned? Did conditions change slightly, etc. I think if you were to ask Jason, he'd say for sure there was a really big difference, but to nail down a number at 18 exactly, might be asking too much.

From my own testing, and my own alternating shot groups, I'd tend to believe these numbers, or, some numbers real close to these. I don't own any 6mm 1K guns, but, a bullets a bullet. If you told me you could make a 30 cal bullet vary by 24" of vertical, I'd be reluctant to disagree.

I'd be willing to bet that with some movement on the 18" and some movement on the BC gain you predict, you could probably hit some common ground. And I certainly would not discount either set of predictions.
 
Charles:

Check out the old threads I found. After I posted the titles, someone posted the links. (Info in the prior thread on this board). The 58 bullets that Jason tested came from me out of the Pindell die. You can read all that info in the old links. Additionally, the old links show the details of Jason's testing and the pictures. The testing was round robin, i.e., one shot with the closed meplats and one shot with unaltered meplats -- with the closed meplats printing about 18" higher with a group about 1/2 the size. Bryan Litz's analysis of Jason's testing is also in these old threads. Lots of info there.

Again, find me some 106 CR and let me do my thing and send them back to you. I already know what the results will be. Post the results here. You don't need a program to tell you what will happen -- what happens will let you fit the program analysis to the results.

Jim
 
Charles et al,
An interesting sidebar to this discussion. At the 1000 yd Nationals just concluded I was shooting my 6.5-284 with
Sierra 142MK trimmed, tipped (Hoover) and molyed. MV 3065 fps. I was getting low on ammo so I grabbed 10 older
142's that were coated, but not trimmed or tipped. I just was going to use them as bbl foulers/moly up the barrel.
Now I will preface this by saying these were not ogive or weight sorted as were the match bullets, but same load/MV.
Guess where they printed?

Bottom of the target compared to centered on the trimmed and tipped versions.

Now I will admit that there are way to many variables to conclude anything from this, espicially since we were seeing a fair amount of vertical shift just do to wind conditions. (germaine to your point of impact comment Charles). But it just seems to add another bit of antecodal evidence to the discussion.
Thought you guys might be interested.

Regards,
Greg
 
Charles, w/regard to wind drift, I think you should focus on T-LAG rather than TOF for answers to 'interesting'.
Also, Hoover's pointing is taylored to the specific bullet nose to continue the radius, reducing influence to shockwave charactor.
Makes sense to me that you could not change the radius at the first 1/8th"(only) for free.
I don't know, wouldn't you create turbulence or a secondary shockwave?
And reshaping the entire nose to another radius is got to have a price or two. Like removing lead in the nose would move Cg backwards, requiring more twist, etc.. Something along those lines

According to my CR106 measurements/program similar to Bill Davis's, this bullet would have a ICAO G1 BC of .520@2950fps with a meplat of .050. I measured .038 on mine but maybe that's what JB had with his, and maybe .520 wasn't taken to ICAO. But to increase BC up to .567 same conditions would mean pointing the meplat to .025, assuming doing so lengthened the nose ~5-6thou.
I think it's reasonable, especially if he had reamed first with Kevin Cram's trimmer.
They're in the same neighborhood.
 
Mike,

As I read Bryan's material, it seems that a two-type nose, say both tangent and secant, might have some advantages. Not exactly what he's saying I suppose, but a reading between the lines.

Generalizations on tangent vs secant ogive nose design can be found at:

From http://www.appliedballisticsllc.com/bulletdesign.html

I’ll try to address the two types of ogives in terms of ‘optimal aerodynamics’.

For a given length nose, there is an infinite number of geometries to go from the meplat diameter, to the full caliber diameter. Two well known geometries are the tangent and secant ogive. Others are the cone, Sears-Haack, ¾ power law, and the paraboloid. The efficiency of the ogive design is judged by how much energy is required to ‘shock’ the air into a compression wave. In other words, the nose needs to make way for a cross section of 1 caliber in diameter to move thru the air at supersonic speed. The efficiency of the nose design depends on how ‘gently’ the nose parts the air. The less energy required to ‘shock’ the air, the less ‘wave’ drag the nose has.

At low supersonic speeds, the optimal ogive shape is a curved shape, approximating a short radius, tangent ogive. As Mach number increases, the optimal ogive begins to look more like a cone with straight edges leading to a sharp juncture with the bullet shank, ie, more like a secant ogive with a long radius.

Using mathematical techniques, ‘optimal’ ogive shapes have been designed that are neither tangent or secant. The problem with these ‘optimal’ designs is that they are only ‘optimal’ for one Mach number. That’s because the ‘optimality’ is based on the geometry of the shock cone, which changes with projectile velocity. The best the bullet designer can hope for is to go with the nose design that’s optimal for the average velocity of the bullet.

One more thing on ogive design: The value of designing a throat lead angle to match an ogive depends on how fast the cartridge will erode the lands.
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This quick reply sucks... Type a reply, click the reply to thread button, it wipes it out... life is too short for this. You must be sure to click on "Post QUICK Reply"
 
Mikecr:

If I recall correctly, the 106 CR had a rather large meplat like many costom bullets. That is one reason that closing the meplat on that bullet made such a large difference as the % of closure to the 6mm dia was more.

You bring up another very interesting topic: the secondary shoulder on many closed meplats vs. a meplat that tracks the ogive closely. With the Pindell die, Ferris made me 4 closing fixtures with different angles. Of course, one fixture would do a nicer job on certain bullets than another. After thousands of rounds tested, I found that a somewhat more pointed meplat actually shot better than one that flowed more evenly with the ogive. Don't ask me why -- I can guess and I have nothing scientific (or even pictures of tests like those done by Jason Baney) but here is my thought. With certain bullets, using certain closing fixtures, I could actually "reshape" if you will the profile of the bullet leading to the meplat (by accident and not design until I noticed the difference on the target). That is to say that the fixture in question "appeared" to have improved the BC of the bullet itself with the same amount of closure of the meplat in light of the point of impact. Bryan Litz may say this in an incorrect conclusion, and I will bow to his credentials -- but this is what I have seen many times.

Seems like I recall that you have made your own BR bulelts (might have you mixed up with another shooter). If so, you may be famaliar with the following. I have found that you take a batch of bullets with exactly the same base to ogive measurement and the OAL of the projectile can vary as much as .020 -- either because of boat tail varriance or varriation of the ogive from the bearing surfact to the meplat. I have also found batches of bullets sorted to exactly the same OAL that DID NOT have the same ogive profile from the bearing surfact to the meplat, and accordingly, the meplats would close differently.

When I am closing meplats in a section of my shop which is, for all intents, sound proof, I can hear and feel the difference in meplat closing (thus OAL) easily at .005 and as small as .001 and .002 on a really good day with top shelf bulelts. If a bullet is short, the meplats will not enter into the fixture as much, and they will not close as nicely -- you can feel and hear this. Having said that, I have closed bullets that "felt and sounded" short only to find that they were just fine -- maybe even long. What happened? The ogive leading to the meplat and the resulting meplat itself formed a profile that closed "easier" and very small. How could this be? My conclusion is that the bulelts are simply not the same due to difference is lube etc during the bullet making process -- as if they had not only been made in different dies producing different bullet profiles. Of course, I have found this with commercial bullets, but I have also found this with some custom bullets. Again, I don't really know why, but I do know the results as this issue often arises. Maybe the bullet makers can give us a heads-up.

Food for thought,
Jim
 
Jim

If I recall correctly, the 106 CR had a rather large meplat like many costom bullets.
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Either you don't recall correctly, or there is a large variance in 106 CRs. The lot I had of 1,000 had some of the smallest meplats I've ever seen in an unaltered bullet (ones that had to be knocked out of a point-up die with a pin). As I said way back in the earlier post, when Tooley put plastic tips in these bullets, they gained almost nothing in reducing meplat diameter.

Whatever, we're quibbling over one bullet, and it is the rest of your post that's most interesting. If nose shape can significantly effect a bullets performance, and if we can control that with aftermarket tooling, we're on to something else that's quite big.
 
If we're really talking about 5-10% gains in BC, that should be measurable with the regular TOF type stuff that the bullet makers do. Perhaps Mr. Litz could do a few tests for the 3rd Edition of his book to quantify the gains...

And if 5-10% is real, it won't be long before the bullet makers start doing this for us.
 
Damon said:
And if 5-10% is real, it won't be long before the bullet makers start doing this for us.
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Damon, we are talking between 5 an 10 percent, there is no question about that. I dunno Why Jim Hardy though I was bashing the idea. I simply thought that there could be more than one element at play, and if so, we'd shove things in the 10 percent region farther and faster the more we knew.

As to the manufacturers doing it, don't hold your breath. Sierra was trying as early as 2004-2005, even earlier, for all I know. They were pursuing the tipped bullets (how many can guess where I got green tips I have?). Last I heard, which was a few years ago, the needed change in the manufacturing workflow to accommodate this was too great.

IIRC, the Nosler and Hornady tipped bullets offer very much the same numbers as the repointed & trimmed. As far as I can tell, neither makes exactly the same untipped bullet, or we could compare tipping versus repointing. Tooley did a little tipping, but only meplat trimming.

Jim Hardy's tooling might allow him to try it. The test would be to get a good plain bullet, insert tips on 10 or 20, then close the points on 10 or 20, and see what, if any, performance differences there were.

But Jim already has answers that satisfy him, nothing for him to gain by running such a test. I believe with his Pindell equipment, he can exceed the performance of a tipped bullet. I don't know what he paid for it, all he would say was "A LOT." And he is not a parsimonious man ("generous" would be more apt). For those of us unable to get that kind of tooling, it could be the tipped bullets offer all the advantages of a Whidden or Hoover die.
 
Charles:

Do you remember the lot of Hornady A-Max 6mm bullets that shot so well for Bob Crone? They really hammered. After that lot was gone (he had a substantial supply), the next lot forced him back to the green box. I know you remember the sorting done by Charles Bailey with his Berger 210's -- one sorted batch hammered. The next sorted batch (with a wider spread) out of the same lot was shot the next year and that lot was fine for score but not so much for group. All shot out of his "Blue" stretch barrel tube gun (about 165 pounds I believe). I paid a lot of attention of how little it takes to change the performance of a bullet and barrel combination. As CB's rifle would "speak the truth" on the line, it made it easier to rely on his findings. When all is said and done, it seems like nothing really changes that much -- it is still all about bullets and barrels.

Yes, the Pindell package (with all the 22 days of R&D) cost more than any competiton rifle I have ever owned. In fact, it was painful. But, it was Ferris Pindell and I KNEW we were on to something very special. Thereafter, Ferris sold a few dies (not exactly like mine :) ), for around $450. He even gave a few to friends. Ferris was that kind of man -- so full of excitement and joy over new-found tools in his kit that he just had to share it -- hid nothing from the precision shooting community.

As a point of interest (or maybe not), we all know that J4 jackets/cores have tighter tollerances than others. Certain bullets made with "thin" J4 jackets can be modified very nicely; however, there is a point when the "thin" J4 jacket will tell you to stop. The "thicker" J4 jackets, and some of the SMK offerings will allow more play time. An example: I can take the old flying grape, low BC Sierra Palma bullet (2155) and close the meplat on this tangent ogive right along the original ogive to meplat line -- very nice. The difference out of a 308 Palma rifle with the closed vs. the unmodifeid meplat is significant (I will leave the exact number alone). However, I can take that same 2155 Palma bullet BUT reshape the upper part of the ogive as it leads into the meplat, to include a meplat closure that DOES NOT track the original ogive to meplat design, and I can get that bullet to shoot amost twice as flat as the before mentioned meplat closure at 1000! As I have mentioned in another thread, you can load the old 2155 Palma bullet with EXACTLY the same load as the new 2156 Plama bullet (all unaltered), at the same sight setting that brought the old 2155 into the X ring and the new 2156 will almost shoot out the top of the 1000 yard prone target! There is just that much difference, i.e., what I did to the 2155 made it a closer brother to the 2156. This could be done because the Sierra jackets will take the modification.

I know I have some one-off Pindell gear, but some of Kevin Kram's tooling does an outstanding job along the lines of my Pindell mini lathe. Kevin's products are top shelf and very affordable. The Whidden and Hoover meplat closing dies are also affordable in light of the difference to be made on the target. One advantage of these meplat closing dies is that they allow you to adjust on the fly. In the 1000 BR game where not nearly as many rounds need to be prepped as in the long range prone and F-Class games, you can make all the meplats look the same -- even on a lot of bullets with considerable OAL and Base to Ogive varriation. Some of the "stuff" I do with the Pindell setup is because I just enjoy the journey. Much of it is not pratical for most shooters who have no interest or desire to take the time to learn the "tricks" that really make a difference. In that regard, the Whidden and Hoover are great dies, and when combined with Kevin's tools, very nice work can be done at an affordable price.

Off topic in many ways, but I have learned a lot being around some of the best smallbore prone shooters in the country. The AMU will often shoot at my home range. If you want to see what "picky" is with ammo, just sit and listen to Olympic and World Champions talk about their ammo. Different fps nodes. Different bullet shapes. Different lubes on the bullets. On and on. Some of these things make a HUGE difference and they really pay the big bucks for the ammo (of course the AMU takes care of there shooters). There are certain contingencies that test in Germany and get the great majority of the lots that shoot on a World Class level.

There is always so much to learn about bullets and barrels. As we get older and or eyes fail, I often wonder how many barrels and bullets we have left in us. I hope you and I and Joel will have a chance to sit down to a good steak again and share our thoughts and experiences on these topics. Oh yes, add David Tooley and Scott Fletcher to the mix and we could create a lot of memories.

Favor Center,
Jim
 
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Jim,

Yes to all you said. I do indeed remember Charles Bailey's 3 tests to grade bullets, and Bob Crone's fortune on that prototype lot of A-Maxes. Then there was my solution -- shoot BIBs. I still remember when I talked CB into buying 1,000, and he called me on the phone, all excited, saying "sorting them is a waste of time!" So why am I still interested? R.G.'s BIBs solve only one problem, consistency. It is a good design, but conservative, as most good designs tend to be.

What your work has shown is that there are other places we can work on a bullet, and hopefully soon, we can quantify and model that, so the improved design will produce bullets just as consistent as we can get now, either with or without sorting -- and if needed, develop whatever tools are needed to sort bullets with modified points.

What I would hope is that some younger people are following this thread, and can investigate the effects of nose shape on bullet performance. I know it is not going to be me, I'm just too tired and in too much pain. Matches 3 and 4 are at Butner Saturday. In matches 1 & 2, I took a HG relay win in score and another in group. As you probably remember, it is the relay placement that determines the 6 and 10 match aggs, so I'm in a good position. To go, all I have to do is drop powder and seat bullets. I'll probably be able to talk myself into that, but maybe not. I have cases I've promised myself to clean and anneal for the past two years, still not done that.

The only contribution I can realistically make to this sport these days, is to push hard enough on people like you to write out clearly what you've done and found. All the little details, rather than the sweeping conclusions, no matter how warranted the conclusions may be.

To only apparently change the subject: I have a good friend who is a book designer, and he's writing a book on that topic. I convinced him to add a chapter by a type designer -- one who makes some of the tools used by a book designer, and by a "typesetter" (good ones are called compositors), who take the plans a book designer draws up, and in some fashion -- limited to extensive -- works over the type from the type designer, to make a better book. Before the 20th century, typesetting involved much of the aesthetic contribution to a book, not so in the 20th century; tradesmen only. But with digital type, "typesetters" now have the tools to work over the rough offerings from type designers, and make a superior product.

By all accounts of preliminary readers, those two chapters are the most exciting of the forthcoming book.

Sound like what you're doing with bullets?
 
I was just checking my email real quick before leaving for the NRA show and had a message that lead me here. Interesting discussion.

Being low on time I'll hit the high points.

1) The 9% gain in BC implied by the 6mm 106 gr bullet test is higher than average. Two big factors make this believable: a) VLD style nose (I'm assuming this, not having seen this specific bullet), and b) mention to the fact that the lot of bullets tested had larger than average meplats 'out of the box'.

9% is certainly above average BC gain from pointing. Consider the following examples of BC gained from pointing (Whidden die). All the following testing was done with the original die insert, prior to the two other angled inserts being available. Tests were done with TOF measurements (not drop). The tests were done back-to-back, so the comparison between the numbers is very high confidence.

.22 cal
Berger 70 gr VLD: +5.5%
Berger 77 gr BT: +2.2%
69 gr SMK: + 1.9%

6mm
Berger 105 VLD: +3.1%
Berger 108 BT: +3.1%
Berger 115 VLD: +4.1%

7mm
Berger 175 XLD: +7% *large meplat
Berger 180 VLD: +2 to 3% *small meplat, multiple tests
Berger 180 Hyb: +8% *large meplat
Sierra 175 MK: + 2%

.30 cal
Berger 155 BT: +1.5%
Berger 155 VLD: +4 to 5% *multiple tests
Berger 155.5: +1.3*
Sierra 155 Palma (2155) +1%

My general conclusion is that the greatest gains in BC are realized when:
1) the meplat is large to begin with, and
2) secant ogives

Note that pointing secant ogives with the original (old) insert resulted in a sharp discontinuity (corner) where the base of the pointed cone meets the ogive. I don't believe this corner has a bad affect compared to a smooth juncture. It's true that the corner will generate a weak shock that costs energy in the form of drag. However, by blending the two 'ramps' with a smooth radius, the supersonic airflow still changes state in a way that costs energy. The only difference is that rather than an expansion shock, there is an expansion 'fan'. Not as visible or abrupt as a shock, but still 'costs' the same. From an energy balance point of view, it's like skiing straight down the hill on the steepest part of the hill vs winding your way around. You still start and end at the same points and have the same net change in potential energy, the only difference is the path.

All the above is small beans IMO. When I was designing the new angles for Whidden die inserts, I concluded that 3 angles would maximize the BC gains for the wide range of bullet ogives. BC gains (typically 2-4% with some exceptions exceeding 5%) can be had by pointing. Discussing the exact shape of the point is (IMO) not worth worrying about. Your talking about a difference that's well under 1% in BC.

Now, if there's something about one method of pointing that makes it more mechanically repeatable, and leaves a rounded shoulder, you might conclude that the rounded shoulder has a flight performance advantage based on groups being smaller. However, the smaller groups are caused by the mechanical repeatability and not the rounded shoulder.

Oh crap, I've got to get on the road. Michelle's gonna be mad if she has to set up the booth by herself!

Take care guys. I hope I can re-engage the conversation from Pittsburgh later this week, but can't count on it!

-Bryan
 
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Bryan:

With your credentials and position with Berger -- as well as your World Class shooting ability -- you may have more upon your shoulders than you realize. Who has this combo to advance the application of long range ballistics to our long range games? No one that I can think of. Berger's agressive development program of the Hybrid projectiles and other offerings is a tremendous contribution. Keep the ball rolling for all of us as "You Are THE Man" in all of this!

Favor Center,
Jim
 
And THAT was what I wanted to know. Thanks, Bryan. Nothing like a few tests to get some concrete info out there.
 
Charles E said:
The only contribution I can realistically make to this sport these days, is to push hard enough on people like you to write out clearly what you've done and found. All the little details, rather than the sweeping conclusions, no matter how warranted the conclusions may be.
Click to expand...

Have you considered a book of your own? I'd buy it.
 
this would be easy to test in a big bore with lathe turned bullets

Law Dawg said:
Mikecr:

If I recall correctly, the 106 CR had a rather large meplat like many costom bullets. That is one reason that closing the meplat on that bullet made such a large difference as the % of closure to the 6mm dia was more.

You bring up another very interesting topic: the secondary shoulder on many closed meplats vs. a meplat that tracks the ogive closely. With the Pindell die, Ferris made me 4 closing fixtures with different angles. Of course, one fixture would do a nicer job on certain bullets than another. After thousands of rounds tested, I found that a somewhat more pointed meplat actually shot better than one that flowed more evenly with the ogive. Don't ask me why -- I can guess and I have nothing scientific (or even pictures of tests like those done by Jason Baney) but here is my thought. With certain bullets, using certain closing fixtures, I could actually "reshape" if you will the profile of the bullet leading to the meplat (by accident and not design until I noticed the difference on the target). That is to say that the fixture in question "appeared" to have improved the BC of the bullet itself with the same amount of closure of the meplat in light of the point of impact. Bryan Litz may say this in an incorrect conclusion, and I will bow to his credentials -- but this is what I have seen many times.

Seems like I recall that you have made your own BR bulelts (might have you mixed up with another shooter). If so, you may be famaliar with the following. I have found that you take a batch of bullets with exactly the same base to ogive measurement and the OAL of the projectile can vary as much as .020 -- either because of boat tail varriance or varriation of the ogive from the bearing surfact to the meplat. I have also found batches of bullets sorted to exactly the same OAL that DID NOT have the same ogive profile from the bearing surfact to the meplat, and accordingly, the meplats would close differently.

When I am closing meplats in a section of my shop which is, for all intents, sound proof, I can hear and feel the difference in meplat closing (thus OAL) easily at .005 and as small as .001 and .002 on a really good day with top shelf bulelts. If a bullet is short, the meplats will not enter into the fixture as much, and they will not close as nicely -- you can feel and hear this. Having said that, I have closed bullets that "felt and sounded" short only to find that they were just fine -- maybe even long. What happened? The ogive leading to the meplat and the resulting meplat itself formed a profile that closed "easier" and very small. How could this be? My conclusion is that the bulelts are simply not the same due to difference is lube etc during the bullet making process -- as if they had not only been made in different dies producing different bullet profiles. Of course, I have found this with commercial bullets, but I have also found this with some custom bullets. Again, I don't really know why, but I do know the results as this issue often arises. Maybe the bullet makers can give us a heads-up.

Food for thought,
Jim
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just make the nose of the bullet with a "more pointed meplat"---or whatever----would be interesting to get someone to try it---I know you cannot point them but it would be easy to see what shape is ballistically superior---I think the minor weight variations produced would be negligible if using the really big .338's or .50's
 
Bryan, Jim,

Something in these numbers doesn't add up. First of all, I have 105, 106 and 100 grain Clinch River 6mm bullets. I believe they are all made with the same point-up die, the 105 and 106 just have a slight a difference in lead, the 100s are made on a shorter jacket, like the Berger 95VLDs.

The bullets I have look like the are a high-number tangent ogive. The meplats are quite small, the same as, or slightly smaller than, the Berger 95 VLDs.

I'm assuming these are the bullets Jason Baney used for his test, which showed an 18-inch higher bullet strike. The are the ones I referred to as Tooley inserting plastic tips, which gave no improvement in my testing.

On the other hand, if the meplat could be reduced to .010, the JBM program *predicted* the gain in BC (reduction in drag) could almost account for the 18-inch strike.

I don't have very many of the 106s left, but enough for a test, if it can be a controlled test. I have a lot more of the 105s if they would do. We could ask Greg Sigmund if they all used the same point up die -- to the best of my knowledge, he had only the one 6mm . . .

Secondly, Jim reported:

I can take the old flying grape, low BC Sierra Palma bullet (2155) and close the meplat on this tangent ogive right along the original ogive to meplat line -- very nice. The difference out of a 308 Palma rifle with the closed vs. the unmodified meplat is significant (I will leave the exact number alone). However, I can take that same 2155 Palma bullet BUT reshape the upper part of the ogive as it leads into the meplat, to include a meplat closure that DOES NOT track the original ogive to meplat design, and I can get that bullet to shoot almost twice as flat as the before mentioned meplat closure at 1000! As I have mentioned in another thread, you can load the old 2155 Palma bullet with EXACTLY the same load as the new 2156 Plama bullet (all unaltered), at the same sight setting that brought the old 2155 into the X ring and the new 2156 will almost shoot out the top of the 1000 yard prone target! There is just that much difference, i.e., what I did to the 2155 made it a closer brother to the 2156. This could be done because the Sierra jackets will take the modification.
Click to expand...

This doesn't seem to jive with Bryan's reported 1 percent increase in BC

Sierra 155 Palma (2155) +1%
Click to expand...

A one to 2 percent improvement in BC (on the G-1 scale) isn't very interesting. It just about gets back what you lose with trimming. I suppose that's a plus, as Larry Bartholomew's raw data showed some bullets with a .010 ES of BC (10 shot groups), but it's not terribly exciting. And the JBM drag/twist formula at least hints of higher gains available.

Are we just going to leave it here?
 
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