One drag model more accurate then another?

[5RWill]

For the longest time i've been using G1 and typing in the G1 BC and so on. Comparing the G7 drag model with the G1 of a 175gr Berger BT match for instance there is a 1/10 mil difference at 1000yds. Is it a preference kind of thing? The results are near similar so which to choose. I had read G1 was for flat based, G5 for BTHP, and G7 for bullets like the VLDs.

 

[Lindy]

Re: One drag model more accurate then another?

Your questions may be answered in this thread:

http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=2410692&page=1

 

[5RWill]

Re: One drag model more accurate then another?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body">Your questions may be answered in this thread:

http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=2410692&page=1
</div></div>

Thanks for the link. I was reading around at JBM but they recommended buying a "applied ballistics" explaining it and all.

 

[Lindy]

Re: One drag model more accurate then another?

That would be this:

http://www.appliedballisticsllc.com/index_files/Book.htm

I recommend that as well. It will explain a lot of things. I have a copy.

 

[Leaddog]

Re: One drag model more accurate then another?

Don't worry yourself with drag models. Use either to get you there, tightening up is up to you.

Drag models, et al., is way over what you need to think about at your level. Load 43.0 grs. of Varget or Reloader 15 with a 175SMK at 2.800 OAL and have at it.

Notice I did not talk about seating depth, etc.. Later you can go there. For now, use overall length.

You say you have a 5R, so just load like I said and start working on your marksmanship, wind/mirage skills. Get some help with your reloading. Your ES's are way too far apart if they are 100 fps as mentioned in a previous thread.

Drag models should be the last thing you think about right now. Get rid of those 155's. Your rifle can't shoot them effectively.

 

[Graham]

Re: One drag model more accurate then another?

Oops, wrong Thread. By the title I thought it was a discussion about Eddie Izzard.

http://en.wikipedia.org/wiki/Eddie_Izzard

 

[Lindy]

Re: One drag model more accurate then another?

What, not RuPaul?

 

[Graham]

Re: One drag model more accurate then another?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body">What, not RuPaul? </div></div>Nope: Nothng that starts with an 'R' and ends with an 'l".

 

[mouse07410]

Re: One drag model more accurate then another?

Mathematically and theoretically - for Sierra MK, Lapua Scenar and Berger VLD (and similar) bullets G7 drag model is the appropriate <span style="text-decoration: underline">standard</span> model (because they are similar to the standard Type 7 Projectile, and very dissimilar from the standard Type 1 Projectile).

As for the actual implementations - since you probably won't be writing your ballistic calculator yourself - <span style="text-decoration: underline">regardless of the drag model or BC type used</span> some programs tend to be more accurate than others. Programs such as LB3 or QTU build their own (non-standard) drag curves based on some wisdom of their authors.

Thus - if you want to compare projectiles based on their BC, then G7 for the modern rifle bullets is the right one to use. <span style="font-style: italic">Though majority of the bullets on the market come only with G1 BC, and it's quite inflated & hardly usable for <span style="text-decoration: underline">long range</span> predictions. Bryan Litz in his book book gives (banded!) G7 BC for several long range bullets - but there are far more bullets than Bryan could test, measure and document.</span>

If you just want to compute trajectories for different bullets (and maybe compare them this way) - then what drag model the program uses doesn't matter <span style="text-decoration: underline">because the authors likely tweaked those models almost beyond recognition</span> (the Army term is FUBAR - which stands for Forced Unrecognizable By Author's Redefinition [of the standard]

). <span style="font-style: italic">And if they didn't tweak them that far - there'd be no way in hell such a program could accurately predict bullet drop for e.g. 308Win 175gr SMK at 1000m using G1 BC. Which of course matters little to a shooter who just needs his prediction data and couldn't care less how it is computed as long as its accurate = matches reality.</span>

 

[5RWill]

Re: One drag model more accurate then another?

I was wondering if one was more accurate than the other was all.

 

[Chanonry]

Re: One drag model more accurate then another?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Blackops_2</div><div class="ubbcode-body">I was wondering if one was more accurate than the other was all. </div></div>

If you want to be 'accurate' it isn't as simple as that, unfortunately.

Stand by for a blizzard of theory from the scientists but if you just want to plug a number from an existing source into a computer model then it depends on how much effort the provider has put into measuring the bc of that particular bullet. So Sierra stepped G1 bc's or Litz's G7's for the bullets he has measured are better starting points than the single G1 number provided by most manufacturers.

You may still need to tweak velocities and step bc's to get a model that gives you an 'accurate' output.

It is the old cliche, rubbish in = rubbish out, but it depends on how accurate is accurate for you

 

[BobinNC]

Re: One drag model more accurate then another?

Here's an accurate depiction of a Model in Drag......

 

[ChadTRG42]

Re: One drag model more accurate then another?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Leaddog</div><div class="ubbcode-body">Don't worry yourself with drag models. Use either to get you there, tightening up is up to you. </div></div>
+1. Use it to get you close/near the target and fine tune it as you go. At 1K, it's hard to get it 100% correct from a computer running numbers.

 

[texasaero]

Re: One drag model more accurate then another?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body">

http://www.appliedballisticsllc.com/index_files/Book.htm

</div></div>

I second this recommendation. I have my own exterior ballistics code I used Litz's G7 models for a velocity dependent drag model.

 

[mouse07410]

Re: One drag model more accurate then another?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Blackops_2</div><div class="ubbcode-body">I was wondering if one was more accurate than the other was all. </div></div>
As I said - one "pure" model (G7) is more accurate than another "pure" model (G1) for long range rifle bullets. That's the exact (and correct!) answer to your question, taken out of context.

<span style="text-decoration: underline">In practice</span> - when you deal with <span style="text-decoration: underline">implementations</span> (programs and calculators that you can buy) rather than the abstract models - developers tend to tweak those models. I don't know how much G7 model needs tweaking to yield correct predictions (IMHO - not much at all, because the LR rifle bullets fit the model), but conjecture (actually am pretty sure) that G1-based model has rather little of the original G1 curve inside because without extensive mucking it is <span style="text-decoration: underline">not supposed</span> (mathematically) to be accurate for LR rifle bullets. Still, after being uber-f... oops tweaked - programs that chose to start from G1 model seem to compute good/accurate enough trajectory, based on the experience of some good shooters here on SH.

 

[5RWill]

Re: One drag model more accurate then another?

Thanks for the advise and input. Might have to buy "applied ballistics" but gotta get back to reloading a new batch of ammo first.