Anybody calculated AccuBond B.C?

[Thor]

Just curious if anyone's worked up their pet load and truly calculated the bullet B.C for any of these by plugging in the muzzle velocity, weather and drop data into their ballistic software after confirming the drop data in the field.

Looking for an accurate B.C for these bullets:

.277 Nosler Accubond 140 grain
.30 Nosler Accubond 180 grain
.30 Nosler Accubond 200 grain

Nosler has the 140 gr listed at 0.496, Exbal lists 140 gr Accubond at 0.496 as well. Accubond .30 180 gr is 0.507 on Nosler site and Exbal has 0.509 on multiple factory rounds. Accubond .30 200 gr is 0.588 on Nosler's site, Exbal doesn't have a factory 200 gr load listed.

I haven't been able to do this myself since both guns aren't quite finished yet. I guess I'm just wondering if these are close to actual numbers. I've been told that some manufacturers may slightly 'inflate the numbers' for marketing.

Thanks, guys.

 

[Michael Eichele]

I have shot the 200 AB extensivly and found the BC to vary greatly depending on a number of factors. I have shot it as high as .590 and as low as .459

I have also played around with the 180 AB a bit but not enough at LR to really determine a BC.

 

[Steve7mm08]

I am working up 160gn accubonds in my 7MM SAUM, would also like views on the stated BC.

What is the calculation for working out actual BC?

 

[Michael Eichele]

What is the calculation for working out actual BC?

There are calculations for a general BC number that will get you close in some cases. The calculations are complex due to the need for an accurate form factor. Youre better off using calculators made for calculating BC's such as those found in most ballistic software and some online ballistic calculators.Then there is the real world. The best way is to develop your load and then go out and determine your true BC by real world firing tests. Sometimes you will find they are spot on or very close to published and other times you will find they are way off the published number. The best manufacturers can do is give you a "mathematical" estimate and an average. This number will be close for "average" circumstances but could be vastly different if you launch them at higher than normal speeds or lower than normal speeds, spin them too fast or are stabilizing them by bare minimum standards and many other factors which is why it can be labor intensive for us LR types because we dont use average equipment.

Load em up and get out there and shoot em. Use the factory BC to start and make the needed adjustments to your software when they impact either higher or lower than the software tells you they should.

 

[mikebob]

I would do it like meichele says it the best way

 

[Thor]

I have shot the 200 AB extensivly and found the BC to vary greatly depending on a number of factors. I have shot it as high as .590 and as low as .459

Meichele,

I'm surprised you've found your B.C's to vary so widely. I would think that a true B.C would be one of the constant values in the ballistic formula. Weather (temp, altitude, and pressure) will vary by day or location. Muzzle velocity might even vary ever so slightly (wide temperature extremes) but shouldn't be enough to matter..especially with a temp insensitive powder.

Those B.C. values you had were with the weather corrections, based on the specific day?

I guess I don't understand how the B.C would vary so much. I thought the ballistic coefficient was a measure of the bullet's efficiency in flight. I would think that would remain a constant value.

I've read some of your articles/post on a number of your hunts. Congatulations on a job well done. You live somewhere I'd love to hunt someday. Alaska's incredible.

Thanks again,

Jace

 

[Michael Eichele]

I think you are under the impression that I am talking about a wide difference of BC with the same load. This is not the case. Each one of my loads has a very concistent BC. The loads I am using that yield .590 are very concistent. Another load I am using is .459. I can count on .459 being a "constant" for my ballistic calculator as long as I am using the 95.5 BMG load.

When it varies so much it is typically due to a completely different set of circumstances like from one rifle to the next. Or a major difference in the loading components or procedures. For example one of my current loads for my 300 RUM is a 200 ACCUBOND using 95.5 grains of H50-BMG powder that load has been giving me a very concistent BC of .459 It is kind of dissapointing but shoots accurate and doesnt beat up my brass. Another load I have toyed with using 86 grains of RL-25 gave me .590 at least out to 600 yards which is as far as I have shot that load. I get a better BC but it is a very rough load on my brass. Why the huge difference? I dont know, but it is what it is. One load does this, the other does that.

This post will probably get me in trouble with some here but my advice is get out there are try it for yourself. If you shoot and reload long enough, you will come accross some very bizarre experiances, esspecially in the BC department.

 

[Michael Eichele]

Also please note:

It has been quite some time between experiments with the 2 different loads using the 200 AB's. When I tested the 200 AB with RL-25 my barrel was very new. Now I have exceeded 700 shots in this barrel and the 200 AB has not been used for most of that. For a 300 RUM that is about the usefull life. It has only been recently I have played with the 200 AB and H-50BMG. The BC now is quite a bit lower and could be due to a degraded barrel. My personal opinion is that the degraded barrel isnt enough to account for more than .100 of the BC (although I could be off base). Rather my opinion is that that much BC loss is due to both a degraded barrel and much different internal ballistics from powder charges and burn rates. Bear in mind this is ONLY my opinion. The fact remains that I have seen the 200 AB as high as .590 and as low as .459 even in the same barrel just different junctions in its life and in conjunction with different powders/charges.

I hope that makes sense.

 

[Steve7mm08]

Thanks for your advice there Meichele.

Like you said I used the on line drop charts to give me some figures to work on then tested at each range from 300 to 700. some were bang on, others were out by up to 1 MOA.

I intend to try the 162 AMAX next, have heard the BC is accurate on those which I hope will translate to less shots fired confirming the drop chart.

Rgds, Steve

 

[Michael Eichele]

Steve,

I have never shot the 162 AMAX but I have worked with the 155 and 178 AMAX's and have results that were either only slightly lower than advertised or much better. I have shot the 155 as high as .474 and it is advertised at .460 I think. The lowest I have seen for the 178 was .490 and it is advertised at .495. I think you will find the AMAX line to be close whether it be a bit higher or a bit lower. Regardless, the 162 will be better than most 7mm bullets.

 

[AJ Peacock]

Steve,

The 162Amax is the only Amax I've played around with. From a Rem 700 in 7mmRM, (around 3000fps) the BC has always been as close as I've needed it. It is the most accurate 7mm bullet I've used in that rifle.

Good luck,
AJ

 

[Thor]

Meichele,

Thanks for explaining that for me. Yeah, I was thinking you were having wide variations from the same load.

Too bad I'm not shooting a .308 M118 match round, all the homework's been done on that one. Here's my question to the backyard scientists out there.

Any .30 Accubond 180 gr bullet should have the same ballistic coeficient (B.C.) regardless of what .30 caliber gun (i.e 300 RUM, .300 WM, or .30-06) since the B.C is a measure of the bullet's efficiency in flight - compared to the model's 'standard' projectile. Same theory applies to another caliber bullet as well. Right?

Wouldn't the same bullet in a certain caliber have the same B.C since ballistic coefficient is a measure of it's efficiency in flight (drag through the air)?

Now I'm definitely not a scientist but I was told there are multiple 'G' models (G1,G3,G7) and that they are not interchangable but I thought all manufacturers used the same G1 model to compare 'apples to apples'. BTW- I don't know jack about the individual differences between each G model.

Somebody asked how you would determine the bullet B.C. Here's what I'd do:

1. Fire your pet load on a certain day, note muzzle velocity, air temp, barometric pressure.
2. Determine your 'come ups' for different ranges.
3. Plug the velocity and weather and altitude into your software along with bullet B.C. Compare the drop data calculations to your actual field results.
4. If they dont exactly match at the all ranges then change your bullet B.C. value up or down until the software calculations match field data.
5. Write down the numbers you used.

You should now be able to pull up drop data for any hunting condition you need anywhere in the world.

This is why I was curious what guys had for the true BC. I'll post what I find after I shoot them but it should be after the guns are done.

 

[Steve7mm08]

Cheers for that, I am pretty new to this long range game, its alot of fun so far and I am still just getting set up.

Longest shots to date were 525 yds for Sika deer with a 7MM 08 (120 Barnes TSX) and 512yds for a goat with .223 (55gn spire points)

The 7MM SAUM will be my long range baby and I hope to take deer sized animals out to 800 yards with it.

Heres the rifle, Sendero with Leupold Mk 4

currently using 160gn Accubonds seated out to just touch the lands, I had the magazine box extended with a Wyatts box. Using 64.5gn Vithavourhi N165

I shot this group at 600yards the other day in a nice breeze while verifying drop chart data, I was most happy

 

[Steve7mm08]

Heres a couple of pics of a local area for feral goats where I tested the Accubonds on goats

white billy goat in centre picture, shot four goats here at 230yds, not hard shots by any means but interesting to see how the 160's went