Range Report G7 and Lapua's 170-gr Lock Base

[uvson]

Hi,
I'm looking for the BC G7 for the Lapua's 170-gr Lock Base.

I would like to compare to Lapua's 155-gr Scenar with ballistic explorer

I have 878m/s (verified) with the 155gr and nearly 820m/s with the 170gr, but wich choose!!

Thank you

 

[mark5pt56]

Re: G7 and Lapua's 170-gr Lock Base

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Julien</div><div class="ubbcode-body">Hi,
I'm looking for the BC G7 for the Lapua's 170-gr Lock Base.

I would like to compare to Lapua's 155-gr Scenar with ballistic explorer

I have 878m/s (verified) with the 155gr and nearly 820m/s with the 170gr, but wich choose!!

Thank you

</div></div>

I show .525 for the Lapua 170 lock base fmj bt. From Exbal program.

Mark

 

[Graham]

Re: G7 and Lapua's 170-gr Lock Base

Julien, ca va?

Avec Exbal, 170HPS, pour moi ca marche avec un(e) seul(e) BC de .521.

For the Scenars I use Sierra's multiple BC's for the 175SMK.

 

[uvson]

Re: G7 and Lapua's 170-gr Lock Base

Hello Graham and Mark

Merci, ca va bien!!
C'est gentil d'ecrire en francais.

thanks for answers.

ok for BC G1, but I'm looking for the G7. This is the BC use in LR

Beyond 600m, you need to have a real ballistic table. The G7 works well!!
http://en.wikipedia.org/wiki/Ballistic_coefficient

 

[buffybuster]

Re: G7 and Lapua's 170-gr Lock Base

Julien,

I would initially start with a .240-G7 BC to get a workable dope chart. Take that out to the range, chronograph some loads to get accurate MV and start shooting at distance and start comparing your actual drops with the calculated drops. Afterward, it should give you some data so you can back into a more accurate G7 BC.

 

[Jeff in TX]

Re: G7 and Lapua's 170-gr Lock Base

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Julien</div><div class="ubbcode-body">Hi,
I'm looking for the BC G7 for the Lapua's 170-gr Lock Base.

I would like to compare to Lapua's 155-gr Scenar with ballistic explorer

I have 878m/s (verified) with the 155gr and nearly 820m/s with the 170gr, but wich choose!!

Thank you

</div></div>

Usually I could help you with this but I'm on the road on business and I don't have my conversion equations with me, but if you don't get it by Wed evening I'll be happy to figure it out for you.

However I have a question? Why are you assuming that bullet will use a G7 coefficient drag model and not a G5 coefficient drag model?

 

[Jeff in TX]

Re: G7 and Lapua's 170-gr Lock Base

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Julien</div><div class="ubbcode-body">Hi,
I'm looking for the BC G7 for the Lapua's 170-gr Lock Base.

I would like to compare to Lapua's 155-gr Scenar with ballistic explorer

I have 878m/s (verified) with the 155gr and nearly 820m/s with the 170gr, but wich choose!!

Thank you

</div></div>

Julien,

As promised here you go.

Lapua 155-gr Scenar
G1 BC = .505
G5 BC = .319
G7 BC = .253

Lapua 170-gr Lock Base
G1 BC = .525
G5 BC = .332
G7 BC = .263

Hope it helps

 

[uvson]

Re: G7 and Lapua's 170-gr Lock Base

Hello Jeff,
thank you a lot
sorry for delay, I was out my home during some weeks.
I want G7 BC because, it gives me real ballistic data behind 600m
On SH, I've found a post with 155gr Scenar .234g7 & .459g1


Thanks again

greetings from France

 

[Jeff in TX]

Re: G7 and Lapua's 170-gr Lock Base

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Julien</div><div class="ubbcode-body">Hello Jeff,
thank you a lot
sorry for delay, I was out my home during some weeks.
I want G7 BC because, it gives me real ballistic data behind 600m
On SH, I've found a post with 155gr Scenar .234g7 & .459g1


Thanks again

greetings from France </div></div>

Julien,

For the 155gr Scenar I got the .505 G! BC off of Lapua's website and converted that to the G5 & G7 BC's

Glad I could help!

 

[JL]

Re: G7 and Lapua's 170-gr Lock Base

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Julien</div><div class="ubbcode-body">Hello Jeff,
I want G7 BC because, it gives me real ballistic data behind 600m
On SH, I've found a post with 155gr Scenar .234g7 & .459g1
</div></div>

Yes and no.
Yes, G7 can be very close or at best same when supersonic.
For example, G7 doesent take account bullet wobble at transition.

And No, G7 is not <span style="font-style: italic">real</span> measured data based on that specific bullet.

Instead, Cd -values are based on true, bullet radar measurements which are as close to truth than basically any amateur -program can be at the moment.

See link:
http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=1210983#Post1210983