G1 or G7????

[dylan5588]

When using a ballistics calculator such as Hornady, if I enter a .224 40 gn hornady vmax bullet with a stated bc of 0.200 should I enter G1 or g7 into the system? simple terms please as I am new to all this, I read the other post on "G1orG7" and it all went over my head!!!

Regards Aj

[1967spud]

thats the g1 figure

[dylan5588]

I am still scratching my head!!!!! so the bc value that Hornady quote of 0.200 refers to a G1 calculation and G7 is something different, so if G7 is better suited to a boat tail bullet like the vmax how can I get a bc value for G7 model????? ( should have stuck to a bow and arrow!!)

[dylan5588]

I am still scratching my head!!!!! so the bc value that Hornady quote of 0.200 refers to a G1 calculation and G7 is something different, so if G7 is better suited to a boat tail bullet like the vmax how can I get a bc value for G7 model????? ( should have stuck to a bow and arrow!!) And how do you delete a post if you do as I have just done?????

[1967spud]

the g1 and g7 figures refer to co efficents for bullets iof different form facters (shape) the g1 is for a flat base standard form facter and the G7 is for a boat tail type form factor

 

 

this expanation is in a very simple and broadly description there is a lot more to it

[1967spud]

just use the g1 figure as i cant find a published g7 atm

[1967spud]

the g7 figure will be nearer .191 with a 4.7% overestimate

[dylan5588]

I think I need to do some reading up on this and other subjects,

[1967spud]

no mate just shoot youre rifle itll blow youre mind and confuse you silly

[dylan5588]

I just entered all my figures into the Hornady calculator using the 0.200 g1 model, then the Figure that you gave me for G7 model and the results were quite a bit different!!! for eg bullet drop at 300 yds was over 3 inches less with the G7 model, II am surprised at the difference

[gbal]

no mate just shoot youre rifle itll blow youre mind and confuse you silly

Broadly,probably true.

It might help to think of G1 as the original system for calculating BC,based on conical (artillery) shells.Most bullet manufacturers used it as it was the only system.

G7 was developed later,and is based on a boat tail shape,but there was no uniform move among bullet manufacturers /ballistic calculators to adopt it.....though some did.Brian Litz has published some/many G7 values,but you just need to be careful not to cross compare (one bullet on G!,another on G7).There are differences,but you need to field fire any loads to check any ballistic calculator anyhow,so it's less of an issue that it might seem (not all bullets ae boat tail etc either).You can go a long way in reloading without mastering every nuance of ballistics (like BC changes anyhow with velocity),and for that matter ever possible subtle measure or fine tuning.

The wind -because you cannot judge it accurately all the way to target-will cause more error than almost anything else,though that is no reason not to consider some other factors.But bullet weight differences of say .2 g are not really worth sorting out,for example,nor need powder be measured more consistently than say .1 g .Don't even consider Coreolis effects.....just be aware that groups at 100 will seldom be just 3x bigger at 300.

Basics are straightforward - but you do need to be aware of them,so do read a couple of standard basic accounts.Enjoy,don't worry about standardising your meplets (holes in the end of bullet)-they are fine as is.

Gbal

[dylan5588]

Ballistics is a subject that interests and facinates me, I like to think of it as a hobby within a hobby, and I love to gain knowledge, I only shoot vermin, rabbits and foxes within my job and sport,, and don't have the need to know how fast or how much a bullet has dropped at 1000 yds, I know what my rifle is doing at a given range up to about 200 yds, which is the max I feel comfortable and confidant shooting it, (.22 k hornet) But as I said ballistics interest me, and since I have been on here it has Whetted my appitite even more, So you are all to blame for me turning into a swatty nerd!!!!!! LOL

[shooter79]

Applied Ballistics by Brian Litz, if you want a deeper understanding of your ammo even out to 200yds than this will be a great read for you.

 

Regards]

 

Carl.

[dylan5588]

Thanks Carl,

Regards Aj

[Dustyman]

Just FYI and not trying to be a@&l , Brian's book quotes 0.188 For g1 and 0.096. For G7 . The first couple of chapters of his book are available on the net if you want a taster and it does delve into the maths a bit and I'm sorry to say goes a bit past me in some areas as my concentration time isn't what it used to be , but as a reference book is very usefull . Many many more on this site with far far greater knowledge than me but thought this might help if you were interested , atb

[dylan5588]

Thanks for that, I did come across the G7 0.096 figure and compared it to Hornadys quoted figure G1 0.200 They only started to differ significantly after 300 yards, And if I use your g1 0.188 I don't think there will be hardly any difference at all, certainly not until after a much greater distance that a KHornet is capable of shooting to!!!!!

[gbal]

Aj,

Apart from the obvious drop and wind effects,which the kHornet makes pretty clear,you have no real concerns practically with sub 200 y ballistic factors,though the improved BC of modern Hornet bullets has given it a decent new lease of life.

 

Interest in ballistic is fine-for external dynamics,BD (Brown Dog,moderator on here) had a good description article on the raft of influences on bullet flight-it should still be available here.As has been suggested,almost anything by Brian Litz is sound-you may have to just accept the math,but he is quite good at explaining,and some issues are just a bit complex.I can't think of a better 'authority', and he is theory and data driven,and not judgemental,and also very clear when 'conclusions' are derived from 'assumption',as sometimes they have to be (BC values are an example).Well worth the effort,takes rifle precision and accuracy way beyond the 'BC/group size at 100y' starting point;and is very sound on the practical limitations for extended range shooting(which goes way beyond,but includes....as before).

Good reading,and enjoy

Gbal

[That bald headed Geordie]

Aj,

Apart from the obvious drop and wind effects,which the kHornet makes pretty clear,you have no real concerns practically with sub 200 y ballistic factors,though the improved BC of modern Hornet bullets has given it a decent new lease of life.

 

Interest in ballistic is fine-for external dynamics,BD (Brown Dog,moderator on here) had a good description article on the raft of influences on bullet flight-it should still be available here.As has been suggested,almost anything by Brian Litz is sound-you may have to just accept the math,but he is quite good at explaining,and some issues are just a bit complex.I can't think of a better 'authority', and he is theory and data driven,and not judgemental,and also very clear when 'conclusions' are derived from 'assumption',as sometimes they have to be (BC values are an example).Well worth the effort,takes rifle precision and accuracy way beyond the 'BC/group size at 100y' starting point;and is very sound on the practical limitations for extended range shooting(which goes way beyond,but includes....as before).

Good reading,and enjoy

Gbal

Hi George, just a mild criticism of the entry above. IT IS NOT MATH....... IT IS MATHS.

Just a thing I have as I know I blow a fuse internally when we this side of the pond take on the American version.

Right. Grumble over. Now back to my bagels and coffee.

[Laurie]

 

Thanks for that, I did come across the G7 0.096 figure and compared it to Hornadys quoted figure G1 0.200 They only started to differ significantly after 300 yards, And if I use your g1 0.188 I don't think there will be hardly any difference at all, certainly not until after a much greater distance that a KHornet is capable of shooting to!!!!!

 

Yes, you've come to the correct conclusion. First G7, as others have pointed out, is based on a long streamlined nose + serious boat-tail design of 'reference projectile' which is pretty similar to a modern long-range HPBT match bullet. (It's actually based on artillery shell designs that appeared from the 1970s which as is usually the case, preceded what we do thanks to the sheer level of money spent on military research.) While the Hornady V-Max is a boat-tail design, it's not in the same design league as the 'G7 reference'.

 

Secondly, as you've divined, there isn't a lot of discrepancy between G7 and G1 results at short range. It's only really beyond 600 yards that you start to see major changes and up to 300, there's nothing between the two forms in terms of results. This applies particularly to relatively low BC bullets at relatively low velocities.

 

The real value G7 offers to many long-range target shooters is the ability to model retained velocity accurately. Even today, we constantly see combinations quoted for .308 Win loaded with rather ballistically lacklustre BC match bullets at modest MVs that are allegedly 'supersonic at 1,000 and will therefore perform just fine' based on G1 BC outputs. Run it through a G7 program and you often find the bullet will be transonic beyond 700 or 800 yards and drop through the sound barrier under most atmospheric conditions just short of 1,000 - a recipe for strange results, exaggerated wind effects, and in some cases instability.

[dylan5588]

Thank you Laurie, are you the Laurie of Laurie Holland fame?? if so I love reading your articles such as in Sporting Rifle.

Regards Adrian

[1967spud]

thats him

[Laurie]

yes - and thanks for the kind words. Laurie

[gbal]

Hi George, just a mild criticism of the entry above. IT IS NOT MATH....... IT IS MATHS.

Just a thing I have as I know I blow a fuse internally when we this side of the pond take on the American version.

Right. Grumble over. Now back to my bagels and coffee.

Les,apologies.It was an homage to Brian Litz,and any newbie who might reasonably think the technical stuff might be easier in the singular.

How are your bagels-hope they are proper kosher ones,I was just going for a cappucino,and waffles,but as a penance ,I'll have tea and a roll-or is that a bap?

Have a nice day,y'all

 

Gbal