Meplat effect on BC

[jsthntn247]

Will these two bullets have a different bc? The more pointed one was .020 longer base to tip and undoubtedly went farther into the pointing die.

 

[Keith Glasscock]

Maybe.

Tell me about the dimensions. What is the meplat diameter of each? What caliber?

There is a definitive point where additional pointing has no beneficial effect.

 

[DocUSMCRetired]

Short and simple answer is yes. By how much, maybe a percent or two, have to fire them to find out.

 

[bill123]

Curious what pointing setup you are using to get the one on the right to close up that much?

 

[jsthntn247]

These are 115 dtacs straight out of the box. Oal of bullets varied .027. The longer the bullet the steeper the point.

 

[spclark]

The longer the bullet the higher the potential BC for that bullet.

Trimming meplats so bullet length is consistent then pointing them up in a secondary operation inproves BC consistency but overall there's a small loss of BC from shortening them.

I recall reading somewhere (either Litz or Whidden) that the improvement is around 5% for each operation but that's in BC consistency not net gain. So I'm guessing that the pointier bullets in that box may have a BC up to 5% higher than the shortest bullets, which doesn't really amount to much in reality.

 

[jsthntn247]

The longer the bullet the higher the potential BC for that bullet.

Trimming meplats so bullet length is consistent then pointing them up in a secondary operation inproves BC consistency but overall there's a small loss of BC from shortening them.

I recall reading somewhere (either Litz or Whidden) that the improvement is around 5% for each operation but that's in BC consistency not net gain. So I'm guessing that the pointier bullets in that box may have a BC up to 5% higher than the shortest bullets, which doesn't really amount to much in reality.

I've got to disagree with that last statement. A 5% difference at 1k is 9" and at 1300 yards its 27" of vertical difference possibility from shot to shot just based on the bullet profile and not the ES of the load coming into play ( nor the wind). That's a miss every time and if your first shot happens to be high because of the sharper nosed bullet your more apt to miss the rest because you can't figure out what the heck just happened and get frustrated or dial the scope.

 

[Bryan Litz Ballistics]

In response to the last two posts...

When I measure BC's in live fire testing, I record the SD of the BC measurement. Typically, it's 0.001 to 0.003, with 0.002 being the most common number. +/-2 SD's gives you the 95% confidence interval, which for an SD of 0.002 is 0.008 range of BC. For something like a .30 cal 185 Juggernaut, this represents less than 3% of BC variation. And remember, this measurement variation isn't just the bullet, it also includes the measurement uncertainty which can be around 0.5% to 1%.

In summary, it's typically not the case that bullets come out of the box with 5% variation in BC.

I'm not saying it isn't possible. The pictures shown in the OP are an example of very inconsistent meplats which probably result in at least 5% variation in BC. Longer bullets like the 6mm 115 DTACs are harder to make with consistent tips due to the length and excessive drawing.

Most boxes of bullets have much less than 5% variation in BC, but it is certainly possible that some boxes have more than 5%. And *IF* your bullets do have 5% of variation within a box, then uniforming them thru trimming and pointing can eliminate most or all of that variation.

When asked the common questions: "should I point?", "should I trim", "should I point and trim, or trim then point, etc..." My answer is that it depends on the shape of your bullets to begin with. If you open the box and all the meplats are the same, then you won't improve consistency at all by any amount of trimming and pointing (though you can improve the average BC by pointing). But if you open a box and can visually see a large variation in the size and shape of the tips (like those in the OP) then you can probably improve the BC uniformity and resulting vertical dispersion a great deal at long range by trimming and/or pointing.

It just depends. Look at what your working with and make a decision based on that rather than applying a blanket process which may be unnecessary.

-Bryan

 

[jsthntn247]

In response to the last two posts...

When I measure BC's in live fire testing, I record the SD of the BC measurement. Typically, it's 0.001 to 0.003, with 0.002 being the most common number. +/-2 SD's gives you the 95% confidence interval, which for an SD of 0.002 is 0.008 range of BC. For something like a .30 cal 185 Juggernaut, this represents less than 3% of BC variation. And remember, this measurement variation isn't just the bullet, it also includes the measurement uncertainty which can be around 0.5% to 1%.

In summary, it's typically not the case that bullets come out of the box with 5% variation in BC.

I'm not saying it isn't possible. The pictures shown in the OP are an example of very inconsistent meplats which probably result in at least 5% variation in BC. Longer bullets like the 6mm 115 DTACs are harder to make with consistent tips due to the length and excessive drawing.

Most boxes of bullets have much less than 5% variation in BC, but it is certainly possible that some boxes have more than 5%. And *IF* your bullets do have 5% of variation within a box, then uniforming them thru trimming and pointing can eliminate most or all of that variation.

When asked the common questions: "should I point?", "should I trim", "should I point and trim, or trim then point, etc..." My answer is that it depends on the shape of your bullets to begin with. If you open the box and all the meplats are the same, then you won't improve consistency at all by any amount of trimming and pointing (though you can improve the average BC by pointing). But if you open a box and can visually see a large variation in the size and shape of the tips (like those in the OP) then you can probably improve the BC uniformity and resulting vertical dispersion a great deal at long range by trimming and/or pointing.

It just depends. Look at what your working with and make a decision based on that rather than applying a blanket process which may be unnecessary.

-Bryan

I'll just buy 115 vlds and point them myself more than likely.

 

[Bryan Litz Ballistics]

don't overlook the 105 hybrid. Much more speed for only being 10 grains lighter, less bearing surface for copper fouling and pressure.

Lots of guys shooting awesome groups and scores with the 105 Hybrid.

-Bryan

 

[JHardy]

Bryan:

Thanks for your ongoing posts to this board as it is an education to all who are serious about their 600 to 1000 yard game. I give you an Amen to everything you have said in this post, but I have observed something a little different since 2002 -- and especially in the last 12 months of extensive testing. Here is what I have found:

This even goes back to Jason Baney's testing of the 106 Clinch River bullets out of the box vs. 58 I sent him that had the meplats closed with the Pindell. All the meplats were very uniform out of the box. Also when I want to check this out, I place a large amount of bullets into a bullet board with the meplats facing up. In just moments you can pick out the "culls" and end up with great meplats from the get go.

In Jason's round-robin testing with his Championship light gun in 6BR, the unmodified bullets shot a very nice 5 shot group at 1000 yards (1022 at the PA club?) in the 5" range. The bullets with the meplats closed -- no other sorting or trimming -- shot about 18" higher. That was nothing new to me as I had already run that test. BUT, the closed meplats shot in the mid 2" range with about half the vertical.

I like to sort base to ogive and as to meplat uniformity using bullet board. Without exception, especially with the 6mm offerings, the smaller the meplat, the more uniform the vertical of the match grade bullet. This is with the 105 Hybrid, 108 BT, 103 Vapor Trail, 103 Spencer, 107 SMK, 104 BIB, 105 BIB Flate Base, 95 BIB Flate Base, Barts 105, etc. I don't know exactly why but in reading my Litz library materials, I tend to believe that the flaws get sucked up into such a small meplat that they are less a factor than exist in good but larger meplats If I had not done so much testing, the sample would be too small to make a call, but that is what I have found -- every time.

Of course there may be other variables. I have worked on a certain lot of Hybrids that have a dead nuts to less than .001 BTO. Same with a certain lot of 108s and some Lapua 105s. Great bullets all and the same result. Educate me here as I am taking my best shot at the reason for the improved vertical uniformity with already great meplats and bullets after a detailed meplat modification.

As an aside, I have found in commercial and some custom bullets, that the internals of the bullet near the meplat are not uniform. There are some that look like a full metal jacket just below the meplat. Others have core material very close to the meplat like the old 300 grain SMK. It may be that a uniform trim and or an internal uniformity process helps on these issues. I can only guess.

Long ago I realized certain basic truths, one form Ferris Pindell and the other just hit me in the face: 1) Accuracy is the culmination of tremendous trifles, and 2) things that are different are not the same. Maybe all these little things stack up to make uniformity on the loading bench and on the target.

Often I don't know the answer to what I am observing, but if the observations hold, they speak for themselves. Vertical uniformity is what I am observing. But why? Thanks in advance for your education and help.

Jim Hardy

Hardy Custom Bullets, Inc.
Passion + Precision = Perfection

Shop: 770-886-1997
Cell: 770-855-8960

 

[jsthntn247]

I can usually only get the meplats to close 50% before I see the base to ogive measurement change. I'm guessing that doesn't matter or you have some way to close them without moving bto.

 

[butchlambert]

Bryan:

Thanks for your ongoing posts to this board as it is an education to all who are serious about their 600 to 1000 yard game. I give you an Amen to everything you have said in this post, but I have observed something a little different since 2002 -- and especially in the last 12 months of extensive testing. Here is what I have found:

This even goes back to Jason Baney's testing of the 106 Clinch River bullets out of the box vs. 58 I sent him that had the meplats closed with the Pindell. All the meplats were very uniform out of the box. Also when I want to check this out, I place a large amount of bullets into a bullet board with the meplats facing up. In just moments you can pick out the "culls" and end up with great meplats from the get go.

In Jason's round-robin testing with his Championship light gun in 6BR, the unmodified bullets shot a very nice 5 shot group at 1000 yards (1022 at the PA club?) in the 5" range. The bullets with the meplats closed -- no other sorting or trimming -- shot about 18" higher. That was nothing new to me as I had already run that test. BUT, the closed meplats shot in the mid 2" range with about half the vertical.

I like to sort base to ogive and as to meplat uniformity using bullet board. Without exception, especially with the 6mm offerings, the smaller the meplat, the more uniform the vertical of the match grade bullet. This is with the 105 Hybrid, 108 BT, 103 Vapor Trail, 103 Spencer, 107 SMK, 104 BIB, 105 BIB Flate Base, 95 BIB Flate Base, Barts 105, etc. I don't know exactly why but in reading my Litz library materials, I tend to believe that the flaws get sucked up into such a small meplat that they are less a factor than exist in good but larger meplats If I had not done so much testing, the sample would be too small to make a call, but that is what I have found -- every time.

Of course there may be other variables. I have worked on a certain lot of Hybrids that have a dead nuts to less than .001 BTO. Same with a certain lot of 108s and some Lapua 105s. Great bullets all and the same result. Educate me here as I am taking my best shot at the reason for the improved vertical uniformity with already great meplats and bullets after a detailed meplat modification.

As an aside, I have found in commercial and some custom bullets, that the internals of the bullet near the meplat are not uniform. There are some that look like a full metal jacket just below the meplat. Others have core material very close to the meplat like the old 300 grain SMK. It may be that a uniform trim and or an internal uniformity process helps on these issues. I can only guess.

Long ago I realized certain basic truths, one form Ferris Pindell and the other just hit me in the face: 1) Accuracy is the culmination of tremendous trifles, and 2) things that are different are not the same. Maybe all these little things stack up to make uniformity on the loading bench and on the target.

Often I don't know the answer to what I am observing, but if the observations hold, they speak for themselves. Vertical uniformity is what I am observing. But why? Thanks in advance for your education and help.

Jim Hardy

Hardy Custom Bullets, Inc.
Passion + Precision = Perfection

Shop: 770-886-1997
Cell: 770-855-8960

Jim, I lost your address. Email it to me and GM TEC will be coming your way.
Butch

 

[Laurie]

I can usually only get the meplats to close 50% before I see the base to ogive measurement change. I'm guessing that doesn't matter or you have some way to close them without moving bto.

If you point your bullets properly the bullet OALs will change. A GB 'Match Rifle' shooter who was into this sort of thing maybe 10 years ahead of F-Class shooters and who also went down the machined solids so effectively they were subsequently banned by our (UK) NRA allegedly on range safety grounds, said to me: 'point them sharper until they stop growing in length'. If you're doing pointing to such as degree that the BTO measurement changes, I'd reckon that's overdoing it and risks poorer long-range consistency.

With some bullets, such as 7mm Sierra MKs, I've found the amount of closure seems to be greater within these parameters and trimming / pointing is well worthwhile. Berger meplats are so relatively small, and appear so relatively consistent, I rarely point this company's bullets now. I also believe the downside risks may outweigh the likely benefits. The new Scenar Ls come with (in relative terms) large meplats and trimming / pointing of the new 180gn 7mm Scenar has worked very well for me.

 

[Bryan Litz Ballistics]

Jim!

Great to hear from you man, it's been a while.

While reading your accounts and questions about improved vertical dispersion for pointed bullets vs. Uniform but unpointed, I had several thoughts as to possible explanations. However I'd like to include this preface.

When discussing improvements to 5" vertical at 1k, casual readers should understand that it's a very specialised conversation and the issues discussed may not apply to everyone or every shooting scenario.

Consider these unique factors of 105 class 6mm bullets at 1k:
Relatively small and lightweight
Relatively long
Into high end of transonic zone for the last couple hundred yards.
Large meplat vs small.

Considering the above, I can offer the following guess which may explain your observations.

The center of pressure is further forward for the larger meplat. This makes the bullet less stable than a pointed one, all else equal. As the bullet approaches high transonic, stability gets worse. Maybe the improved vertical dispersion of the pointed meplat bullets is due to them being pointed and having a more AFT CP, making them more stable.

we could test this theory a few ways. First, if it's true then there should be less of a difference in vertical dispersion for pointed versus non-pointed bullets 'of a larger caliber'.

Another test would be to look at pointed versus non-pointed 6mm 105 class bullets fired from faster than normal twist. This should put both bullets in a elevated stability state and you should see less of a difference between the two.

I've got to go for now, these are my initial thoughts. I'll keep thinking about it.

Cheers,
-Bryan

 

[JHardy]

Will do Butch.

Jim

 

[JHardy]

You have made a good observation. If your BTO measurement is different after meplat closing, simply treat that as your new BTO and tune your rifle accordingly. In fact, sometimes this change in BTO after closing will be more uniform than prior to meplat modification.

When I was closing meplats for my own bullets, I would just set my tune to the modified bullet, if needed. When you close meplats for customers, they tend to measure everything before they fire a shot. Accordingly, I have developed a technique to keep the same BTO after closing the meplats.

I have been closing meplats on the Original Pindell die that Ferris and I developed in 2002. I also have an array of Whidden closing dies as they are easy to read with my old eyes and the meplat closing inserts were designed by Bryan Litz -- that says a lot. John can even furnish heat treated inserts for those that close a lot of meplats. That is important to me as I just went past the 250,000 mark this week while working on Bart's fine 105. I have developed several techniques that take advantage of the benefits presented by each individual die and closing fixture. That journey has been long and very time and labor intensive -- but very exciting.

Regards,
Jim Hardy

Hardy Custom Bullets, Inc.
Passion + Precision = Perfection

Shop: 770-886-1997
Cell: 770-855-8060

 

[6BRinNZ]

You have made a good observation. If your BTO measurement is different after meplat closing, simply treat that as your new BTO and tune your rifle accordingly. In fact, sometimes this change in BTO after closing will be more uniform than prior to meplat modification.

When I was closing meplats for my own bullets, I would just set my tune to the modified bullet, if needed. When you close meplats for customers, they tend to measure everything before they fire a shot. Accordingly, I have developed a technique to keep the same BTO after closing the meplats.

I have been closing meplats on the Original Pindell die that Ferris and I developed in 2002. I also have an array of Whidden closing dies as they are easy to read with my old eyes and the meplat closing inserts were designed by Bryan Litz -- that says a lot. John can even furnish heat treated inserts for those that close a lot of meplats. That is important to me as I just went past the 250,000 mark this week while working on Bart's fine 105. I have developed several techniques that take advantage of the benefits presented by each individual die and closing fixture. That journey has been long and very time and labor intensive -- but very exciting.

Regards,
Jim Hardy

Hardy Custom Bullets, Inc.
Passion + Precision = Perfection

Shop: 770-886-1997
Cell: 770-855-8060

Not Arguing - I have always pointed until I see this BTO change and then stopped and backed off .001+ (whidden pointer) as I assumed pointing pressure was causing some sort of distortion - the inference being it would be bad. (No testing done to confirm otherwise)

Does your testing indicate its not bad just needs to be consistent?

 

[JHardy]

Your technique of backing out .001 if the BTO is changing will work. However you may lose some of the benefit of additional closing. The BTO will change more on some jackets than others. The J4 jackets will show more change than the Sierra. Some new custom jackets also seem to behave very much like the Sierra. Your suspensions are correct in that it does not matter if the the BTO changes as long as it is consistent and you adjust your seating depth and tune accordingly. But, as you probably know, it can get away from you till you get your system down.

It also matters what closing insert you are using with any closing die. On the Whidden system, the #1 closes great on VLDs. the original #0 has a wider closing and the # 2 has the widest closing. Each closing fixture puts different pressure on the jackets and meplats.

Sometimes a closing fixture that is not designed for that bullet will do a great job. You just have to learn what works best. A tip: use a thin lube on the bullet. If I am using Imperial sizing wax, I have it sitting under a fly tying lamp during my process. That keeps the lube thin without any hydro effect on the bullet. Ballistol also works very well. Just be very consistent with your lube.

Keep you closing dies very clean -- especially the closing insert. Also, keep them tight in the press whether or not you use a #17 o-ring between the press and the lock ring. Run your closing dies in a press that is dead nuts square or floats -- like a co-ax which does a very good job. John Whidden furnishes bullet bases for the co-ax and standard presses.

My Pindell die allows me to be very aggressive. I can close the meplat until it sticks in the fixture if I want. On the Pindell, I have a knock out pin so no big deal. Then I back the fixture off till I have no bulge on the meplat. Then I adjust the die where I can hear and feel as little as little as .001 difference in the bullet length when closing. I also adjust the Pindell so that the bullet gently falls into my fingertips at almost exactly 2 seconds from the closing as I am able to adjust the air suction holding the bullet in the die after closing. When you get down to hearing, feeling and an exact 2 second release of the air suction, you can get very exact with what you are doing -- VERY exact. Even the difference in the drop time tells you that something is different.

A plug for the Whidden system (and yes he is a dear friend of mine): The easy to read lines and numbers on the die are great. The closing fixtures designed by Bryan Litz will close about everything very nicely indeed. Customer service is not just quick but "sudden" on occasions. After having closed over 250,000 meplats since 2002 (as of this past week), a huge asset to my passion for bullet perfection has been learning to combine the Pindell and Whidden systems this year. It has been a game changer for me. Bullets will talk to you and let you know what they like. Learn to listen closely and develop a system that enhances that conversation.

One of the best things you can do is to make a bullet board for the bullets you are meplat closing. Place the bullets base down in the individual holes with meplats facing up. You can easily view 500 bullets, with or without magnification, and sort the meplats for size and uniformity within seconds. A very easy step that will produce a difference you can see on paper. Remember, you want to keep everything the same.

Lastly, shoot great bullets. Life is too short to mess with junk bullets. Yes, even the GREAT bullets can be improved for your 600 and 1000 yard matches. There are higher scores and smaller groups to be had right there at your work bench.

Regards,
Jim Hardy

Hardy Custom Bullets, Inc.
Passion + Precision = Perfection

Shop: 770-886-1996
Cell: 770-855-8960

 

[jsthntn247]

You have made a good observation. If your BTO measurement is different after meplat closing, simply treat that as your new BTO and tune your rifle accordingly. In fact, sometimes this change in BTO after closing will be more uniform than prior to meplat modification.

When I was closing meplats for my own bullets, I would just set my tune to the modified bullet, if needed. When you close meplats for customers, they tend to measure everything before they fire a shot. Accordingly, I have developed a technique to keep the same BTO after closing the meplats.

I have been closing meplats on the Original Pindell die that Ferris and I developed in 2002. I also have an array of Whidden closing dies as they are easy to read with my old eyes and the meplat closing inserts were designed by Bryan Litz -- that says a lot. John can even furnish heat treated inserts for those that close a lot of meplats. That is important to me as I just went past the 250,000 mark this week while working on Bart's fine 105. I have developed several techniques that take advantage of the benefits presented by each individual die and closing fixture. That journey has been long and very time and labor intensive -- but very exciting.

Regards,
Jim Hardy

Hardy Custom Bullets, Inc.
Passion + Precision = Perfection

Shop: 770-886-1997
Cell: 770-855-8060

Not Arguing - I have always pointed until I see this BTO change and then stopped and backed off .001+ (whidden pointer) as I assumed pointing pressure was causing some sort of distortion - the inference being it would be bad. (No testing done to confirm otherwise)

Does your testing indicate its not bad just needs to be consistent?

I was told to back off when bto changes as well. With my .224 90vld's and the Hoover pointer with correct pointing insert I can close the meplats to about a .040 opening with no change in bto. However, I did notice that if I closed them to around .020 (did a few by mistake) that the bto moved only 1/2 thou on all bullets that were "over pointed". Seems the bto movement was consistent across all the bullets over pointed and I did not notice any bulging at the tip but still tossed them. I might purposely do a few like that and shoot them at the end of a string next match and see what happens.