Range Report G7 BC for .308 175 SMK?

[WRM]

Re: G7 BC for .308 175 SMK?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Scimitar</div><div class="ubbcode-body">Bryan
Do you have the G7 BCs of the Lapua 155 Scenar and the Lapua 170
Lockbase?

Thanks
David </div></div>

I know he has the 155 - it's published in his book

Cheers,

Bill

 

[MikeeBooshay]

Re: G7 BC for .308 175 SMK?

I have been following this thread and have certainly learned alot, thanks very much ya'll.

FWIW, I looked in my Ballistics FTE program on my Iphone, and the G7 for the 175 SMK was listed at .252, in the M118LR loading. BUT.... go to the Sierra list of projectiles, and they show a G1 model choice, with 3 steps of BC as velocity dropped. That particular model did not work well in my gun.

I did get my hands on some real M118LR, not much, but enough to play with ( wish I had had a chrono). The model in FTE worked well for that, if I boosted the MV in the model a bit, I was OK with that, since my barrel is a couple inches long and the temp was about 106F. That little program in my phone has saved a lot of ammo developing come up stickers since I got it.

Wish I could find a couple thousand rounds of the real thing.....the LC stuff in the white boxes is close, but not the same.

Again thanks for the great info on this post.

MB

 

[ReaperDriver]

Re: G7 BC for .308 175 SMK?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Mikee B</div><div class="ubbcode-body">I have been following this thread and have certainly learned alot, thanks very much ya'll.

FWIW, I looked in my Ballistics FTE program on my Iphone, and the G7 for the 175 SMK was listed at .252, in the M118LR loading. BUT.... go to the Sierra list of projectiles, and they show a G1 model choice, with 3 steps of BC as velocity dropped. That particular model did not work well in my gun.

I did get my hands on some real M118LR, not much, but enough to play with ( wish I had had a chrono). The model in FTE worked well for that, if I boosted the MV in the model a bit, I was OK with that, since my barrel is a couple inches long and the temp was about 106F. That little program in my phone has saved a lot of ammo developing come up stickers since I got it.

Wish I could find a couple thousand rounds of the real thing.....the LC stuff in the white boxes is close, but not the same.

Again thanks for the great info on this post.

MB </div></div>

Also want to echo that this was a great discussion and I learned a lot. I also have Ballistic FTE (and KAC's Bullet flight) on my iPhone and want to get to the point of using correct data. The G1 models have gotten me on paper and I've had to tweak from there. I intend to work my own dope, but I'd still like to be able to use the ballistic program with as accurate an output as possible.

So to summarize - if I'm shooting 175 SMK, I should be using the G7 models, right? Is the M118LR 175 bullet exactly the same as the 175 SMK and I can use that profile in place of the commercial bullet?

What about the following bullets... are they G5 or G7: 168 SMK, 168 AMAX, 178 AMAX, 155 SMK Palma, 155 Scenar?

Thanks!

 

[Jeff in TX]

Re: G7 BC for .308 175 SMK?

[/quote]

Also want to echo that this was a great discussion and I learned a lot. I also have Ballistic FTE (and KAC's Bullet flight) on my iPhone and want to get to the point of using correct data. The G1 models have gotten me on paper and I've had to tweak from there. I intend to work my own dope, but I'd still like to be able to use the ballistic program with as accurate an output as possible.

So to summarize - if I'm shooting 175 SMK, I should be using the G7 models, right? Is the M118LR 175 bullet exactly the same as the 175 SMK and I can use that profile in place of the commercial bullet?

What about the following bullets... are they G5 or G7: 168 SMK, 168 AMAX, 178 AMAX, 155 SMK Palma, 155 Scenar?

Thanks![/quote]

For the Sierra MatchKings bullets (168 and 175 gr) they will more closely match the G5 coefficient drag model and not the G7. As for the AMAX and Palma bullets the G5 CD would probably hold true also.

The G7 CD model is typically for longer more aerodynamic VLD (very low drag) bullets. Having said that, you may get very satisfactory results using the G7 CD model. Regardless of which drag model you decide to use it’s imperative you use the corrected BC for the bullet your testing/shooting.

Best of luck.

Jeff

 

[TXHunter]

Re: G7 BC for .308 175 SMK?

Great discussion. Here's what I've observed. Using Exbal heavily for the past 5-6 years, it has always predicted more elevation at 1000 than actually needed with my .308/168Amax load. I transitioned to FTE/Iphone early this year (KAC was useless at the time due to major bugs) and it pretty mush matched Exbal - that is too conservative. A week ago, I shot my first .260/140 Amax out to 1000 and both programs are too optimistic, too little elevation. Both cases are using G1 with Hornady published BCs and both have been well chronoed with logs of both site in and existing conditions. Anybody want to propose an explanation?

 

[Jeff in TX]

Re: G7 BC for .308 175 SMK?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TXHunter</div><div class="ubbcode-body">Great discussion. Here's what I've observed. Using Exbal heavily for the past 5-6 years, it has always predicted more elevation at 1000 than actually needed with my .308/168Amax load. I transitioned to FTE/Iphone early this year (KAC was useless at the time due to major bugs) and it pretty mush matched Exbal - that is too conservative. A week ago, I shot my first .260/140 Amax out to 1000 and both programs are too optimistic, too little elevation. Both cases are using G1 with Hornady published BCs and both have been well chronoed with logs of both site in and existing conditions. Anybody want to propose an explanation? </div></div>

TX Hunter,

No flame here, just trying to help. If you’ve read through this thread, it should have answered your questions. Bryan and I as well as a couple other folks have tried to explain all of the short comings of using a ballistic program with a G1 drag model not to mention the published G1 BC. Think of G1 as bad juju with mixed results at best.

Try using the correct coefficient drag model with the corrected bullets BC to match the corrected drag model. JBM on-line will offer you the best ballistic calculator as well as allowing you to try different variables.

Hope it helps,

Jeff

 

[ReaperDriver]

Re: G7 BC for .308 175 SMK?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Jeff in TX</div><div class="ubbcode-body">[/quote]

For the Sierra MatchKings bullets (168 and 175 gr) they will more closely match the G5 coefficient drag model and not the G7. As for the AMAX and Palma bullets the G5 CD would probably hold true also.

The G7 CD model is typically for longer more aerodynamic VLD (very low drag) bullets. Having said that, you may get very satisfactory results using the G7 CD model. Regardless of which drag model you decide to use it’s imperative you use the corrected BC for the bullet your testing/shooting.

Best of luck.

Jeff
</div></div>
Jeff, thanks. From the discussion - the 175 SMKs seemed to fit the G5 definition but everyone talked about using the G7, so I was confused. Also, the military uses the 175 SMK in the M118LR round and they use the G7 model instead of the G5. Further confusion.....

I need to go back through this thread and figure out what the G5 and G7 BCs for my bullets are and compare them against my actual dope.

 

[Lindy]

Re: G7 BC for .308 175 SMK?

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">I need to go back through this thread and figure out what the G5 and G7 BCs for my bullets are and compare them against my actual dope.</div></div>

JBM has Bryan Litz' G7 BCs in their bullet library.

Another way to derive either a G5 or G7 B.C. is to back into it using your actual field shooting data. Of course, to do that you're going to need very accurate long-distance shooting data, as well as precisely recorded atmospheric parameters, not to mention a ballistic program that will use those particular B.C.s.

In addition, if I were going to trust that shooting data for the purpose of deriving B.C.s from it, I'd want to know the muzzle velocity of each individual shot, as well as the precise location of the impact of each shot with respect to the point of aim.

That sounds like a fun research project. Personally, though, I'm just using Bryan's G7 B.C.s, with some slight adjustments to fit it to my field shooting data. I'm pleased to let someone else do my research.

 

[ReaperDriver]

Re: G7 BC for .308 175 SMK?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">I need to go back through this thread and figure out what the G5 and G7 BCs for my bullets are and compare them against my actual dope.</div></div>

JBM has Bryan Litz' G7 BCs in their bullet library.

Another way to derive either a G5 or G7 B.C. is to back into it using your actual field shooting data. Of course, to do that you're going to need very accurate long-distance shooting data, as well as precisely recorded atmospheric parameters, not to mention a ballistic program that will use those particular B.C.s.

In addition, if I were going to trust that shooting data for the purpose of deriving B.C.s from it, I'd want to know the muzzle velocity of each individual shot, as well as the precise location of the impact of each shot with respect to the point of aim.

That sounds like a fun research project. Personally, though, I'm just using Bryan's G7 B.C.s, with some slight adjustments to fit it to my field shooting data. I'm pleased to let someone else do my research.

</div></div>
I feel like a complete idiot, but I just spent 45 min searching though JBM and couldn't find Mr Litz's library of G7 BCs. I did however find the pull down in the actual input page for the caculator that had (Litz) after the bullet type - but it would not update the BC in the input field when I selected it. What am I doing wrong?

 

[Lindy]

Re: G7 BC for .308 175 SMK?

The program will use the BC selected from the bullet library. I don't think it will tell you what it is. However, it's easy enough to figure it out.

Calculate a shot at a long distance using the bullet from the bullet library.

Then enter a guess at a G7 BC, resetting the library field to "None", and calculate the same shot. Adjust the BC until it matches the dope for the shot using the bullet library. Voilá!

Or, you could order a copy of Bryan's book. I recommend it.

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

 

[ReaperDriver]

Re: G7 BC for .308 175 SMK?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body">The program will use the BC selected from the bullet library. I don't think it will tell you what it is. However, it's easy enough to figure it out.

Calculate a shot at a long distance using the bullet from the bullet library.

Then enter a guess at a G7 BC, resetting the library field to "None", and calculate the same shot. Adjust the BC until it matches the dope for the shot using the bullet library. Voilá!

Or, you could order a copy of Bryan's book. I recommend it.

http://www.appliedballisticsllc.com/index_files/Book.htm
</div></div>
OK, good. At least I'm not losing my mind!

 

[hifly78]

Re: G7 BC for .308 175 SMK?

Thanks Bryan for all the great work on your book. Read it cover to cover, a great resource.

With new understanding the transition to G7 has been easy. Also thanks for giving the G1 measured BC's and also the calculated variations on both so an informed decision on which BC to use can be made.

 

[Scimitar]

Re: G7 BC for .308 175 SMK?

tag

 

[TimSues]

Re: G7 BC for .308 175 SMK?

I found this site researching Berger bullets for my 30-378 Weatherby and have been involved with this thread for two days, researching the plethora of information you all have provided. I am a new ballistic junky... But am excited about the opportunity to predict and execute shot placement at ranges in excess of a grand.

Bryan and Jeff thank you for you research and knowledge sharing.

I would like to ask if you have recommendations for ballistic software,(I went to JBM site and they have so many calculators I din't know what product would be best) any suggested ballistic and bullet grain G7 BC (I am liking Berger's product) information for 30-378 Wetherby.

 

[hrt4me]

Re: G7 BC for .308 175 SMK?

great info, thanks!

 

[Bob 964]

Re: G7 BC for .308 175 SMK?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: WRM</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Scimitar</div><div class="ubbcode-body">Bryan
Do you have the G7 BCs of the Lapua 155 Scenar and the Lapua 170
Lockbase?

Thanks
David </div></div>

I know he has the 155 - it's published in his book

Cheers,

Bill </div></div>

G7 BC for the 155 Scenar is 0.236.

 

[hrt4me]

Re: G7 BC for .308 175 SMK?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bryan Litz</div><div class="ubbcode-body">.30 cal 178 grain Amax
G7 BC = 0.240 lb/in^2</div></div>

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bryan Litz</div><div class="ubbcode-body">.224 cal 75 grain Amax: G7 BC = .212
.224 cal 80 grain AMax: G7 BC = .231</div></div>

thanks!