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I keep seeing Ballistic Coefficients described in G1 & G7 figures.

If, as we are led to believe, G1 figures relate to flat based bullets then why do makers such as Hornady refer to the BC of their .308 155 gr. ELD Match bullet as 0.461 (G1) when it is patently a Boat-tailed bullet.  More annoying is they also quote a G7 BC of 0.232.

Just confuses the hell out of me.

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The higher number G1 can be a marketing ploy...its a higher number so may be seen as 'better (by the uninformed) ' than the G7 value of a competitor bullet.

Some may genuinely need to use the G1 in their ballistic app even though G7 is usually more relevant.

The move towards custom drag models  will gradually take root.

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Entering the Bc's in my bal cal with all the other info gets me real close,good enough for my needs

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Custom Drag Models are the way forward really for long range shooting, especially when shooting through transonic and beyond - available in lots of of AB products such as Kestrels etc.

If you’re not shooting ELR however G1/G7s suit most people well. 

Ive always had good success using G1 advertised BCs with G1 models in calculators out to 800m or so, and that’s with boat tailed bullets, I guess the flight profile of the boat tailed bullet will always match the G7 better, but the G1 won’t be too far off. But either are trying to “best fit” the projectile against a modelled curve, where a Doppler radar gathered custom curve (CDM) will always be better at long ranges.

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0.5 moa at 1000yds is pretty reliable  

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Is there a "consumer" ballistic calculator that will get POI within 0.5MOA of point of aim at 1000yds?..............on Stickledown on a windy day?

I'd like to see a demo of that................

Pete

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Hornady are now using Doppler to calculate BC,s on some bullets and show G1, so the statement that G1 is for "Flat base bullets" is redundant I guess.

 

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5 hours ago, Re-Pete said:

Is there a "consumer" ballistic calculator that will get POI within 0.5MOA of point of aim at 1000yds?..............on Stickledown on a windy day?

I'd like to see a demo of that................

Pete

Elevation...!

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Truth is even more confusing.  Simply put, BC's...all of them, are only approximations which attempt to describe the form factor and drag factor of a projectile at a given velocity.  It is also velocity dependant which wrt to trajectory is in itself affected by air density, temperature etc etc (not that these matter at relatively short hunting ranges but they certainly do when you get into long range).  The bible on these things is Brian Litz's "Advanced Ballistics for Long Range Shooting" wherein you'll find all the theory (and maths!) behind this subject.  If you retain just 5% of that book, you'll be doing well!

G1 was initialised to try and predict the trajectory of early ball ammo and basic flat based pointed tip military (black powder) and is based upon that early military bullet form.  G7 is based upon a more streamlined form of spire-point with boat tail which in itself has many variables including length of tip, CoG, angle of boat-tail and length of bullet wall.

It follows that the published figures are either presented in one of two ways:  a G1 or G7 at the stated MV (cheating), or an averaged figure based upon hunting or target distances.  

Some manufacturers use the former but enter it into a Ballistic App and it will provide over optimistic results for drop and drift.  BC sells, it's as simple as that, and that is why so many are happy just to print optimistic G1 figures at MV on the box, which is about as useful as telling you your car has brakes but I've no idea how long it will take you to stop from 60mph!

Sierra almost always quote an averaged G7 figure these days for their boat tailed ammo and by and large, their figures equate well with Doppler radar evaluations at different ranges, with comparisons notably done and published by Brian Litz.

However (isn't there always one?) don't get too hung up on it, as despite what's published every rifle may shoot slightly differently (barrel twist, wear and length as well as chambering all affect the MV) so even averaged G7 won't always give you the required precision based on a stated MV (which most likely won't be your MV).  The only reliable way to calibrate your app is to beg, borrow or buy a chronograph to determine your MV and test your drops from a 100yd zero.  What you'll probably find is that quoted G1 works well for even boat tailed projectiles out to perhaps 300yds but once beyond that, drag and velocity loss really start to matter wrt form, bullet attitude (not the cheeky kind, the geometric kind!) and the effects of wind really start to kick in.  From there out, averaged G7 will provide a reasonable fit but usually not a precise fit.  To get something more reliable, you really need to measure drop (5 shot average group at each target looking for group centre) at 100yd intervals out beyond your intended range (to get a full understanding of trajectory to and beyond your intended target), using your 100yd zero and leaving the scope settings alone....well, nearly as there's a problem with that...

The switched-on will spot the obvious issues when needing to do this out past say 300yds.  Drop and drift (even without wind) may exceed practical target boundaries (well, elevation will anyway).  The answer is to re-zero for the 300yd target and measure drop out to say 600.  For hunting/vermin control, you really probably don't need to go any further and even if you only have the land to get say data to 400 yds it may be enough to help you out.

Choosing an app that allows a starting point whereby you input the stated (average) G7BC, then use tested drop and drift data out to your max tested range and see how that correlates to the app predictions.  You can then in Strelok Pro for one,  alter the BC "actual value" until the app gives you the same or near as damn-it drops.  Whilst you can also alter the MV figure to get a fudged fit, technically an averages BC is better practice imho.  Job done and it should be spot on for your newly developed loads.

This though is just the start.  If you intend regularly, or not so regularly shooting beyond 400 yds with any sort of precision, you'll almost certainly be tripped up unless you also calibrate your app with powder temperature sensitivity and with differing environmental data.  At least for on-target first-shot.  I've been shooting LR for many years now and have come to realise that the more I learn about it, the more I realise I don't know!  That and there's a requirement for fastidious discipline and consistency in home loading to ensure consistency which comes from the right load, and low ES (a must for LR shooting).

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On 6/6/2019 at 10:04 PM, PhilM said:

Custom Drag Models are the way forward really for long range shooting, especially when shooting through transonic and beyond - available in lots of of AB products such as Kestrels etc.

If you’re not shooting ELR however G1/G7s suit most people well. 

Ive always had good success using G1 advertised BCs with G1 models in calculators out to 800m or so, and that’s with boat tailed bullets, I guess the flight profile of the boat tailed bullet will always match the G7 better, but the G1 won’t be too far off. But either are trying to “best fit” the projectile against a modelled curve, where a Doppler radar gathered custom curve (CDM) will always be better at long ranges.

Spot on Phil.

At least where first shot on target counts.  Usually (an I include myself here) most people tend to use the apps with approximations for BC/MV to get on target, then dial in after shooting a series of groups or test shots.  You can take that approach (and why not...it's valid?) for fun shooting, but it's a waste of time for LR vermin control (they don't stand still once a bullet thumps in several feet away) and for comp, you sometimes get very limited...or no calibration shots depending on comp and discipline.  Custom drag models are by miles the best way.

AFAIK, Lapua are the only company currently offering limited custom drag modelling for their bullets, but it's now the defacto mainstay for military sniper training (at least in the USA).

I have to say though I'm surprised to learn that you get "good success" out to 800m using G1 on a stated MV for boat tail bullets.  I've tried many times and its been no-where near (acceptably) close.  G7 seems to model way better once out past 300yds IME.

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Hornady have their "4DOF" calculator that has doppler radar drag data for their own (obviously) and a selection of competitor bullets.   I tabulated 4DOF, Shooter and actuals at Eskdalemuir last month. Using their predictions worked very well for the 300gn Lapua .338 out to 1 mile and a lot better than "Shooter" with G7 data.

The .308 178gn  ELD-M was similarly accurate for me.

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Wasn't aware that they had consumer-user software though?  Handy though having that data if you shoot Hornady bullets.

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Thanks for the heads-up. I'll check out whether they have any data for some I use.

 

Edit.  Just done that and it's spot on wrt to my own data for the 139 scenar at both 600 and 1000yds  That's a handy reference resource.👍

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I tried G7 and found my elevations were way out and found G1 much better for me,I've no I deer why it was way out 🤔,I can't remember exactly but it was a couple of minutes or so keen.

Not sure if the bc for the 7mm 180gr ELD match bullets has been confirmed yet.

Last time I checked it had TBD which may have ment to be determined..!

Again these hornady Bc's are with this doplar radar which is probaly only a gnats willy difference anyway 

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14 hours ago, VarmLR said:

I have to say though I'm surprised to learn that you get "good success" out to 800m using G1 on a stated MV for boat tail bullets.  I've tried many times and its been no-where near (acceptably) close.  G7 seems to model way better once out past 300yds IME.

He is not alone in that experience, although I suspect (no data to support this view) it is coincidence rather than science that it "works". It certainly does not work on demand. With some loads the G1 seems to give a better model than G7 even with the "wrong" bullets.

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19 minutes ago, Chanonry said:

Before we start getting aroused by "doppler radar data".

Hornady 4DOF bull or Ballistic Bitches ? You choose.

4DOF Hype?

Bryan Litz makes a compelling argument against poor commercial practice and hype.  All I can say is '4DOF' gave better results than 'Shooter' for me out to 1mile.  I intend to try 'Applied Ballistics"

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I've found Litz's Point Mass Ballistics Solver to be very good, and the huge tome it comes with is a mine of info.

It's saved me shedloads of time and hassle.

Pete

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Lapua’s 6DOF and TRASOL are almost identical for me in both 6.5x47 and .338NM.

Results have been pretty spot on out to 1000m. 

Ive recently acquired a Kestrel 5700 with AB so it’ll be interesting to see how the regular AB, and the custom DM, compares to the Lapua & TRASOL solvers.

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