We had some jacket failures on a particular type of bullet on a trial I was involved in. I was given the job of predicting where the bits, particularly the solid slug inside the bullet, could possibly go so that we could avoid hitting the helicopter flying near the bullet trajectory. Tends to concentrate the mind if you think you may be blamed so I was fairly generous in my assumptions for the models.
Hornady BCs
- Thread starter CamTheBam
- Start date
We had some jacket failures on a particular type of bullet on a trial I was involved in. I was given the job of predicting where the bits, particularly the solid slug inside the bullet, could possibly go so that we could avoid hitting the helicopter flying near the bullet trajectory. Tends to concentrate the mind if you think you may be blamed so I was fairly generous in my assumptions for the models.
Ballistic coefficient for a bullet is an interesting subject.
Ballistic coefficient is a variable used to compare the atmospheric drag on a bullet to the very carefully measured trajectory of a standard Bullet with a ballistic coefficient of 1.0.
I believe Horanday uses Ingalls tables
https://www.scribd.com/document/17536448/Ingalls-Ballistic-Tables
Because BC is comparison to a standard Bullet (ballistic coefficient of 1.0) the ballistic coefficient changes relative to the ballistic coeffient of the standard bullet as the velocity of the bullet drops.
With doplar radar chronographs and computer technology a bullet manufacturer could assign a Ballistic Coefficent of 1.0 to any Bullet they manufacture - measuring the change in velocity over distance due to air drag and then compare all of theirs Bullets to their new standard (in house) bullet
It took the Brits months firing a 1 pound bullet from a cannon at a pendulum chronograph at various measured distances to establish the British 1909 tables to establish ballistics tables for a bullet with a Ballistic Coefficent of 1.
Ballistic coefficient will vary depending on the original ballistics tables created from firing a standard bullet.
Maybe this is more information than folks want?
Ballistic coefficient is a variable used to compare the atmospheric drag on a bullet to the very carefully measured trajectory of a standard Bullet with a ballistic coefficient of 1.0.
I believe Horanday uses Ingalls tables
https://www.scribd.com/document/17536448/Ingalls-Ballistic-Tables
Because BC is comparison to a standard Bullet (ballistic coefficient of 1.0) the ballistic coefficient changes relative to the ballistic coeffient of the standard bullet as the velocity of the bullet drops.
With doplar radar chronographs and computer technology a bullet manufacturer could assign a Ballistic Coefficent of 1.0 to any Bullet they manufacture - measuring the change in velocity over distance due to air drag and then compare all of theirs Bullets to their new standard (in house) bullet
It took the Brits months firing a 1 pound bullet from a cannon at a pendulum chronograph at various measured distances to establish the British 1909 tables to establish ballistics tables for a bullet with a Ballistic Coefficent of 1.
Ballistic coefficient will vary depending on the original ballistics tables created from firing a standard bullet.
Maybe this is more information than folks want?
That reference projectile is either what we now call the G1 reference, or if not the G1 itself is very close to it. That's why G1 is unsuitable for long-range external ballistics calculations as comparing a long-nose pointed streamlined boat-tail bullet against it is a classic chalk and cheese comparison. Bryan Litz says the standard 40gn LRN bullet used in .22 rimfires is actually close to the G1 'form' and this is one of the few cases where we'd use this measure reliably nowadays.
G7 is the norm now for longer ranges and its reference projectile is that of a modern low-drag artillery shell whose shape is close enough to that of most modern match and some sporting rifle bullets to allow reasonably close comparison, although not close enough for serious ELR competitors who use custom ballistic profiles.
All of the main bullet manufacturers producing long-range products have Doppler radar these days and can track bullets throughout their entire flight giving them the ability to produce true drag profiles. As their customers recognise BCs though, averaged values for both G1 and G7 are usually quoted. In the case of averaged G7, tables, programs, ballistic solver programs and apps etc using it usually work out close enough to actual flights to around 1,000 yards, maybe a bit further as long as the bullet stays well above the speed of sound.
I very much doubt that. They may have short range fixed head muzzle velocity radars but they are simply not good enough at anything other than very short ranges (less than 200 metres). For a true drag profile you need a multi million dollar doppler tracking radar with a fully moving head operated by a top class experienced operator, backed up by fixed head muzzle velocity radars. You can hire them but even then the costs are extremely high.
I like Litz's book with all the G1 and G7 BCs and Form Factors. I noticed Hornady BCs were a bit higher than the ones Litz came up with.
Thanks to Mr Litz, manufacturers are now rather constrained in their claims. It's a bit embarrassing to claim say 0.600 G1 when Bryan comes along with the next edition of Ballistic Performance of Rifle Bullets and quotes the long-range average as under 0.500.
In the bad old days of G1 values only, people could quote very high values without telling out and out lies thanks to the speed-sensitive nature of this metric through choosing whatever velocity flattered the product the most. That's assuming that the claim was based on tests anyway as I've read more than a few times that some manufacturers used a bullet-form based computer program to calculate theoretical BCs and left things at that. I always felt that Sierra played fair here with its speed-banded G1 BC ranges and apparently lowish values compared to some competitors.
Bryan Litz and Berger Bullets have jointly changed the playing field a great deal since those times. Also back then - not so many years ago - very few people regularly shot at 1,000 yards never mind longer distances. Even if wildly optimistic, the quoted G1 values and printed ballistics tables in the back of reloading manuals would get a properly zeroed rifle onto the paper at 500 or 600 yards which was 'long distance' for many. Moreover, few people knew their MVs with any sort of accuracy and relied on the often badly inflated values given in the same reloading manuals' data-sets adjusted for different barrel lengths. [2,750 fps with a 24-inch barrel in the manual; Huh ........ that'll be 2,900 fps with my 26-inch barrel!'
]
At 1,000 yes, I thought they were dropping faster than would be implied by BC, (and drifting more) but I did not think that about them at 600. I blew them up, first, as far as I know. Running 4 Rsaums and several .284’s at the time, a couple years ago, they matched or beat every bullet I tested them against at 600, at a much lower price.
Having never yet delaminated a bullet in flight back then, I had two particularly accurate Saums with twin barrels that actually required a bit of downloading relative to another maker’s, which I presumed wrongly was the throat length or twist rate.
Bore diameter caused my problems. It took a long time to figure that out. Those two barrels were fantastically accurate as .284’s before they were set back to Saum’s, but even then, I had to down load them. In life 2 as Saums, they edged out new barrels at “colder” loads so all seemed good.
In hindsight it’s clear, the necessary downloading by about 1.5 grains in both chamberings had always been attributable to tight bores. It hadn’t mattered as .284’s because they are 200 FPS slower, and in any event ELDM’s weren’t even out yet. The blowup’s were from slightly tighter bores in combination with high speed.
I’d almost wager that every barrel blowing up ELDM’s is running seemingly average or milder charges, but in fact stresses jackets more than average.
I’d also say that the ELDM cannot take high stress as well as blue yellow or green, because since then I shed red and tested those, but that within parameters, - they are hard to beat at midrange.
As an aside I do believe without attempting to understand why, that a slightly tighter than average bore makes more accurate rifle, all else equal.
Brians356
Gold $$ Contributor
They've queered the pitch for the bullet marketers.
-
Too true Ha! Ha!
(Just like affordable home chronographs did for ammunition manufacturers' marketing-led MV claims some years earlier!)
dcali
Bullet Maker
Speaking of calculated values, they're really not that bad. When I started making bullets, I used a modified version of Bob McCoy's McDrag program to calculate BCs (among other things) to help develop an optimal design for my intended uses. I was pleasantly surprised when the BCs I calculated were almost exactly what the bullets' actual BC turned out to be when measured (with my admittedly meager resources). I've also used the software to calculate a bunch of bullets from Bryan's book, and the error is surprisingly small (to me) when compared to his tests. It over-estimates the BC because it doesn't account for any yaw at all, but not by as much as I was expecting, and it's not hard to estimate it once you're aware of the trends. At least for our purposes.
My 1:7 22BR blows up everything. 88ELDM, 95 SMK, and 90 VLD. That's a special case for that caliber I think, but has shown me the importance of not going to 300k rpm or beyond. My future rifles will all be setup to strictly spin bullets less than 300k.
My 6.5 Creedmoor with a 1:7.7 hasn't popped anything and shoots the 147 better than anything else I've tried.
I entirely agree with you about the tight bore! I think it's the primary culprit for bullets popping.
McDrag and programs like it have been good enough for the initial estimates for artillery shells for years and have formed the starting point for subsequent fire control drag laws (just try measuring the zero yaw drag of a shell or bullet in flight).
With yaw drag, it has to be low since, if the yaw is high, you will not be hitting many targets at long ranges. So yaw drag should not have a huge effect on BC which means that the initial estimates should be close with decent software.
The large calibre bullets I was involved in investigating which were popping on a regular basis all had very deep rifling engraving on recovered jackets. In this case though it was one batch of bullets, another batch had no problems at all, possibly combined with a tight bore.
Do you all realise that BC is not an absolute or constant number?
Velocity plays a huge influence on actual BC.
The BC of a bullet shot out of a 338-378 is going to be different than the same bullet shot out of a 338Marlin.
Just saying.
Cheers.
Velocity plays a huge influence on actual BC.
The BC of a bullet shot out of a 338-378 is going to be different than the same bullet shot out of a 338Marlin.
Just saying.
Cheers.
If the correct reference drag law is being used velocity should have no effect on BC at all. That was the whole basis for having different reference drag laws with different shaped drag curves to match the shape of the drag curves for different projectile shapes. There can be differences from bullet to bullet and gun to gun due to bullet yaw but again it should only affect the single value of the bullet BC (i.e. move the drag curve up or down to match the bullet drag curve) not any variation with speed.
dcali
Bullet Maker
This is a pet peeve of mine. Bullet manufacturers (I’m looking at you, Hornady and Sierra). Publish different BCs at different velocities.
In Sierra’s case, it’s because they refuse to use a G7. What they are doing is a pragmatic hack that basically invalidates the entire purpose of a BC - to have one number that relates a bullet’s drag to a standard drag. If the mismatch is so bad that you need to use multiple BCs to get good results then you are doing it wrong (using a poor standard). Sierra does this for historical reasons I assume, but times have changed and it’s not a lot of effort to update their data to modern standards.
But at least Sierra carefully and clearly explains why they do what they do and how to use the numbers. I can’t say the same for Hornady. I don’t understand what Hornady is doing because they don’t explain it, but their velocity dependent BCs are confusing, especially when you consider that they offer a calculator that is supposedly using a bullet specific drag function and not a standard at all. That they don’t tell you what to do with these BCs is mystifying. Are you supposed to use them like Sierra’s? Is it muzzle velocity they’re talking about? Do they match the curves at one velocity? They don’t say in any kind of clear manner.
No wonder shooters get confused. If you’re not going to publish the full drag curve, publish one BC - a G7 usually. If you must, publish one for each standard (G1 and G7) so that shooters can compare bullets easily to companies who only publish G1. Ideally, I’d like to see drag curves and BCs published, but so far, Lapua is the only major manufacturer to do that.
End of rant. Both companies make good stuff and that’s what matters. But I wish they’d get their acts together on this.
In Sierra’s case, it’s because they refuse to use a G7. What they are doing is a pragmatic hack that basically invalidates the entire purpose of a BC - to have one number that relates a bullet’s drag to a standard drag. If the mismatch is so bad that you need to use multiple BCs to get good results then you are doing it wrong (using a poor standard). Sierra does this for historical reasons I assume, but times have changed and it’s not a lot of effort to update their data to modern standards.
But at least Sierra carefully and clearly explains why they do what they do and how to use the numbers. I can’t say the same for Hornady. I don’t understand what Hornady is doing because they don’t explain it, but their velocity dependent BCs are confusing, especially when you consider that they offer a calculator that is supposedly using a bullet specific drag function and not a standard at all. That they don’t tell you what to do with these BCs is mystifying. Are you supposed to use them like Sierra’s? Is it muzzle velocity they’re talking about? Do they match the curves at one velocity? They don’t say in any kind of clear manner.
No wonder shooters get confused. If you’re not going to publish the full drag curve, publish one BC - a G7 usually. If you must, publish one for each standard (G1 and G7) so that shooters can compare bullets easily to companies who only publish G1. Ideally, I’d like to see drag curves and BCs published, but so far, Lapua is the only major manufacturer to do that.
End of rant. Both companies make good stuff and that’s what matters. But I wish they’d get their acts together on this.
I have shot a fair amount of the M118LR out of an M40, the 175 SMK in that combination maintains pretty good accuracy through the transonic. Keep in mind pretty good accuracy is a measure of how well the ammo-rifle-shooter combination can hit the target of interest, in this case the target is larger than most targets we consider in this forum.
Turbulent Turtle
F-TR competitor
Yeah, well just so you know; Hornady lists the G1 AND G7 values for all their ELD Match, ELD-X and their awesome A-Tips. They only lists the G1 BC values for their older bullets, which should not be used for long range anyway.
dcali
Bullet Maker
Yeah, well just so you know; Hornady lists the G1 AND G7 values for all their ELD Match, ELD-X and their awesome A-Tips. They only lists the G1 BC values for their older bullets, which should not be used for long range anyway.
Right. And for some of them (at least- I haven’t looked at them all) they list multiple BCs for one drag function, which is the confusing part.
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