TRUE BC of an Accubond Lr?

[Supercat]

Hello Fellas,
I am going to work up a load for my 7mmRemMag, 26" Criterion barrel, with 1:8 twist using 175gr AccuBond Lr's. I am figuring on getting 3,000fps or close to it.

I also want to buy a calibrated turret knob for the load for my Swarovski X5, and I know how important it is to enter the proper input for it to be accurate at long ranges.

With this in mind, I am wondering what the correct BC is.
Nosler's updated BC for the 175gr 7mm ABLR is 0.648 using G1.
From what I have read, BC changes with twist rate and velocity.
I don't know what twist rate Nosler used for their .648 BC but my twist rate is 1:8"

So how would/do I determine the actual BC for my load?

Any input would be greatly appreciated! Thanks

 

[hunter24605]

http://www.bergerbullets.com/twist-rate-calculator/

Plug in the values, and it'l give you an "adjusted BC"

 

[Supercat]

Thanks for the reply Hunter!

I think that I am missing something because I don't see "adjusted BC" anywhere

What am I doing wrong?

 

[hunter24605]

Thanks for the reply Hunter!

I think that I am missing something because I don't see "adjusted BC" anywhere

What am I doing wrong?

I plugged in your data and it said you are getting FULL BC...Just to see an adjusted BC, switch it to 1:10 and it'l give the adjusted BC and by how much BC is being compromised.

 

[Supercat]

Got it!! Knew that I must have screwed it up

Thank You again SO MUCH! That was too easy

 

[joelkdouglas]

In addition to hunter24605's comment, which is good for the BC compromise:

I would use the G7. Bryan Litz in "Applied Ballistics for Long Range Shooting" discusses the difference between the form factor of a bullet and the relationship to G1 and G7 BCs.

Short version, if you want LR shooting and there's a G7 available for a RDF type bullet, one should probably use the G7 BC instead of the G1.

 

[Supercat]

Thanks!

 

[30-338]

This may help on different between G1 and G7.

http://bulletin.accurateshooter.com/201 ... d-to-know/

 

[jason miller]

In Bryan Litz's book, he shows the 175 ABLR as having an average G7 BC of .330 from 1500-3000 fps. It varies a bit from .338 above 3000 fps, down to .326 in the 2500-2000 window and 2000-1500 window, and then back up to .329 below 1500 fps. G1 is listed at .643 through that same velocity window, with a high of .714 above 3000 fps and a low of .585 below 1500 fps

Seems like part of the advantage of using G7 vs G1 would be having a more similar number throughout the entirety of the bullet's flight.

And interestingly, Litz shows the 168 ABLR as having a slightly higher BC at every velocity, with the averages being .648 and .332. His measurements show the two bullets having exactly the same radius on the ogive, a minuscule difference on the boat tail, and the 175 having a longer nose and shorter shank than the 168, though, which makes me wonder how the 168 could have a higher BC. He states that he uses live-fire results for calculating BC. Maybe he used two different barrels and the rifling engraving was different enough to make the difference in two otherwise very similar bullets? IDK...

 

[Supercat]

VERY interesting Jason thank you!

 

[joelkdouglas]

And interestingly, Litz shows the 168 ABLR as having a slightly higher BC at every velocity, with the averages being .648 and .332. His measurements show the two bullets having exactly the same radius on the ogive, a minuscule difference on the boat tail, and the 175 having a longer nose and shorter shank than the 168, though, which makes me wonder how the 168 could have a higher BC. He states that he uses live-fire results for calculating BC. Maybe he used two different barrels and the rifling engraving was different enough to make the difference in two otherwise very similar bullets? IDK...

I wonder if the higher velocity and shorter flight time makes the apparent BC higher?

 

[30-338]

In Bryan Litz's book, he shows the 175 ABLR as having an average G7 BC of .330 from 1500-3000 fps. It varies a bit from .338 above 3000 fps, down to .326 in the 2500-2000 window and 2000-1500 window, and then back up to .329 below 1500 fps. G1 is listed at .643 through that same velocity window, with a high of .714 above 3000 fps and a low of .585 below 1500 fps

Seems like part of the advantage of using G7 vs G1 would be having a more similar number throughout the entirety of the bullet's flight.

And interestingly, Litz shows the 168 ABLR as having a slightly higher BC at every velocity, with the averages being .648 and .332. His measurements show the two bullets having exactly the same radius on the ogive, a minuscule difference on the boat tail, and the 175 having a longer nose and shorter shank than the 168, though, which makes me wonder how the 168 could have a higher BC. He states that he uses live-fire results for calculating BC. Maybe he used two different barrels and the rifling engraving was different enough to make the difference in two otherwise very similar bullets? IDK...

This is new from Nosler

https://www.nosler.com/accubond-long-range-bullet/

Bryan Litz hasn't made any new comment on the above.

 

[Supercat]

Litz did a whole thread over on the Long range Forum

 

[30-338]

Litz did a whole thread over on the Long range Forum

Bryan Litz hasn't posted on LRH since 2017, so never comment on what I posted

https://www.longrangehunting.com/member ... litz.7848/

You can click his on posting give you last date he posted.

 

[Supercat]

Litz did a whole thread over on the Long range Forum

Bryan Litz hasn't posted on LRH since 2017, so never comment on what I posted

https://www.longrangehunting.com/member ... litz.7848/

You can click his on posting give you last date he posted.

Are you telling/warning me to "never comment on what I posted." ???

 

[30-338]

Litz did a whole thread over on the Long range Forum

Bryan Litz hasn't posted on LRH since 2017, so never comment on what I posted

https://www.longrangehunting.com/member ... litz.7848/

You can click his on posting give you last date he posted.

Are you telling/warning me to "never comment on what I posted." ???

This all I said

This is new from Nosler

https://www.nosler.com/accubond-long-range-bullet/

Bryan Litz hasn't made any new comment on the above.

Sure he's made pass comments but again he hasn't commented on what I posted.

I have no say on who can post or give warnings and if you take my post that way, so be it.

 

[Supercat]

Litz did a whole thread over on the Long range Forum

Bryan Litz hasn't posted on LRH since 2017, so never comment on what I posted

https://www.longrangehunting.com/member ... litz.7848/

You can click his on posting give you last date he posted.

Are you telling/warning me to "never comment on what I posted." ???

This all I said

This is new from Nosler

https://www.nosler.com/accubond-long-range-bullet/

Bryan Litz hasn't made any new comment on the above.

Sure he's made pass comments but again he hasn't commented on what I posted.

I have no say on who can post or give warnings and if you take my post that way, so be it.

Got it, and thank you for the reply my friend!

And SORRY that I misinterpreted what you said