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BC for .308 145g FMJ-BT

This is a discussion on BC for .308 145g FMJ-BT within the Ammunition forums, part of the M14 M1A Forum category; Can anyone cite the value of and source for the ballistic coeffcient (BC) of a .308 145g FMJ-BT? I need the BC for the ballistic ...


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Old January 8th, 2013, 01:35 PM   #1
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Question BC for .308 145g FMJ-BT

Can anyone cite the value of and source for the ballistic coeffcient (BC) of a .308 145g FMJ-BT? I need the BC for the ballistic calculator software so I can create an MOA table for this load.

In have 1000s of these 145g FMJ-BT bullets from Wideners. I also have 1000s of 150g .308 Hornady FMJ-BTs. The 145s perform quite differently from the 150s. I know the BC for the Hornady 150s (from their website) is 0.398. But I gotta believe the 145 BC is as different from the 150 BC as it's performance is from the 150s performance. So I've been trying to find a BC for it online, but can only find BCs for 150 and 147. And even across the different 147g M80 bullets used by different MFGs I have found variances in the BCs reported.

I found this for Winchester 147g WB ...

http://blog.hsoi.com/2010/12/13/winc...-coefficients/

... which cites a BC for the 147g @ 0.421.

Then there is this M14TFL thread ...

NATO ammo coefficients

... that cites a BC for the 147g @ 0.393.

Here're the bullets. Left = Hornady 150g FMJ-BT, Center = TopBrass 150g FMj-BT, Right = Wideners 145g FMJ-BT:


I suppose I could use an average of the two 147 BCs, but I figured I'd ask here first in case anyone has the real BC.

Thanks in advance.

15th

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Old January 8th, 2013, 01:44 PM   #2
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check out this website. just sign up its free. its the best ballistics calc on the web, and its practically identical to my nightforce software...
since g7 scopes are nightforce scopes...

http://www.gseven.com/ballistic-program

federal 150 is .408
winchester usa 147gr is .418

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Old January 8th, 2013, 08:25 PM   #3
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I think you will find that the Wideners bullet will give better performance over the others, part of that is it has a better boat tail angle. I suspect there Lithuanian production.

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Old January 9th, 2013, 06:15 AM   #4
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Not hijack the thread, but how does the BC of the 7.62 FMJBT M80 bullet compare to the BC of the 30 Cal. FMJFB M2 bullet?


Last edited by Sailormilan2; January 10th, 2013 at 07:55 AM.
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Old January 9th, 2013, 09:02 AM   #5
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Unless you have proven test data for the three bullets in question, you're just guessing. Most published BCs are no more than guesses made by somebody else. As far as entering data into a ballistic calculation, a good guess is all that you need. Don't forget, you will also be guessing on other input, such as the environmental factors. In the end, the results aren't going to vary that much and they need to be verified by actual firung.

I'd use .400 for the boattail M80 and .340 for the flat base M2.

JMHO

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Old January 9th, 2013, 12:17 PM   #6
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I see where you were already sent a link to a BC calculator. Here is another...along the left side of the linked page. You then put the given BC into the program and it gives you a lot of targeting data. I've used it for some time with good results! Good luck.


http://www.handloads.com/calc/

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Old January 9th, 2013, 12:25 PM   #7
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jbm ballistics has a file of BCs for most commercial bullets. Since very few bullet BCs have been determined by actual testing, I suppose most of them are calculated. Not that there's anything wrong with that, or that it really makes any practical difference.

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Old January 9th, 2013, 01:48 PM   #8
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Quote:
Originally Posted by raymeketa View Post
jbm ballistics has a file of BCs for most commercial bullets. Since very few bullet BCs have been determined by actual testing, I suppose most of them are calculated. Not that there's anything wrong with that, or that it really makes any practical difference.
I'll check that out.

And as you said in your earlier reply, there are so many factors and a few others are mere guesses anyway, so I think you're right. It's just an estimate. For this 145g Wideners bullet I took the average of the 2 BCs for the 147g and plugged it into the Point Blank Ballistics software that I have, and the MOA table for the 145g calc shows elevation adjustments (in inches) that are almost identical to the 150g load I also put into the software.

For a 300-yard ZERO, the MOA tables show the following for a 100-yard target distance ...

300-yard POI adjustment
A. 145g @ +5.37
B. 150g @ +5.29

400-yard POI adjustment
A. 145g @ +8.56
B. 150g @ +8.45

500-yard POI adjustment
A. 145g @ +12.11
B. 150g @ +11.97

... meaning, for example, that if you sighted in for a 300-yard ZERO using a 100-yard target you'd want the POI at about 5.5 inches about BE, etc.

So since they are that close, I think your supposition is spot on. I'll take the trajectory data with me to the range when next I shoot and validate the software at 100 and maybe even 300 yards. I've chrono'd my loads so at least that factor is accurate.

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Old January 9th, 2013, 02:15 PM   #9
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Quote:
Originally Posted by Mainzer View Post
I see where you were already sent a link to a BC calculator. Here is another...along the left side of the linked page. You then put the given BC into the program and it gives you a lot of targeting data. I've used it for some time with good results! Good luck.


http://www.handloads.com/calc/
Thanks Mainzer. I tried it and got a BC of 0.426 for a .308 145g Boattail; which seems a bit high to me. The ballistic data that was produced was similar but not quite the same as the Point Blank Ballistics (PBB) software results I calc'd earlier. I also tried the 0.407 (avergae) BC I used in the PBB software and it pretty much matched up for the 300 and 400 yard zeros when using a 100-yard target: +5.68" and +13.50" respectively. But for the 500 it shows +35.96" compared to the +12.11" POI adjustment from the PBB software. So now I am concerned because that's a delta of over 23".

One or both of these programs may be off. I guess I'll have to validate at the range.

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Old January 10th, 2013, 10:11 AM   #10
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Information from Prvi Partizan of Serbia, the company that makes that bullet, states that it's ballistic coefficient is 0.404.

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Old January 10th, 2013, 11:28 AM   #11
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Quote:
Originally Posted by Phil McGrath View Post
I think you will find that the Wideners bullet will give better performance over the others, part of that is it has a better boat tail angle. I suspect there Lithuanian production.


I'd have to nix that on the Lithuanian Production. I've got some of the pre-nato designated loaded ammo. I've pulled some down and the weigh 150gr rather than the 145gr shown here. Also the cannalure is similar to the type on the Hornady bullets, and not rounded as the 145gr bullets. Maybe others can add more info. dozier

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Old January 10th, 2013, 05:22 PM   #12
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Quote:
Originally Posted by John Coleman View Post
Information from Prvi Partizan of Serbia, the company that makes that bullet, states that it's ballistic coefficient is 0.404.
Ok then. I suspected the Wideners 145g 308 was a PRVI bullet but I didn't know for sure. So this is good news. I'll plug in the 0.404. I was close with the 0.407 average I used from the 2 147g rounds. Thank you John.

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Old January 10th, 2013, 05:38 PM   #13
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I wish I had 1000s or 147 Gr FMJ-BT. You would not want part with a Hundred or two would you?

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Old January 10th, 2013, 05:42 PM   #14
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Quote:
Originally Posted by raymeketa View Post
Unless you have proven test data for the three bullets in question, you're just guessing. Most published BCs are no more than guesses made by somebody else. As far as entering data into a ballistic calculation, a good guess is all that you need. Don't forget, you will also be guessing on other input, such as the environmental factors. In the end, the results aren't going to vary that much and they need to be verified by actual firung.

I'd use .400 for the boattail M80 and .340 for the flat base M2.

JMHO

Ray
+1 most calculators will allow you to verify BC and velocity by measuring your drop at different ranges. IE zero for 100, then shoot at 200 and 400 input the data for the weather and the observed drop and you'll have a pretty good baseline.

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Old January 11th, 2013, 01:57 PM   #15
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I got the 0.404 figure from the 2012 Prvi USA catalog. I found my personal record of the Privi website from 2006 and translated from Serbian and the factory loaded velocity is slightly different with the ballistic coefficient listed as 0.419 for the same bullet.

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