Differences in BC

[FOTIS]

Barnes lists a BC of .398 for the 165 TSX 308 caliber.

When this bullet was launched from a range certified 30-378 WBY the Oehler 46 read the BC as .471. Is this not weird?

 

[Ridgerunner665]

At that velocity...the rate of spin is MUCH, MUCH faster (I'm guessing its a 1/10 twist)...recent studies (Litz) show that spinning bullets faster increases BC, up to a point anyway...plus the higher velocity helped too, Barnes probably averaged it based on several predictions under varying conditions...the lower BC is probably close to right from a 308/30-06.

 

[Ridgerunner665]

It would be interesting to see data from same bullet/rifle combo at 300 and 600 yards...it would likely show a good example of why Sierra uses stepped BC's.

 

[Ridge_Runner]

only bullet I ever worked with that I didn't hafta change the BC to make my charts match my trajectory is the lapua 139 gr scenar (and it sux for hunting)
the .284 160 AccuBond is advertised at .531, I run it 3575 out of my 7mm AM 9 twist, I run the BC at .62 to get my charts right to 1500 yards
the .264 berger 140 has a published BC of .618 (use to be .64 back before the yellow/orange box days) I run it at 3280 from my 6.5 gibbs 8 twist, I run the BC at .7 to make my charts match the actual trajectory to 1200 yards. this is a couple of examples that I recall the numbers.
RR

 

[FOTIS]

Very interested indeed!

 

[HOGWILD338-378]

http://www.bergerbullets.com/12/
The differences in BC's is explained in this article pretty well and it's not that they have changed but that they have been measured wrong for ages! Brian Litz has been testing all kinda bullets to see what the discrepancies were and explained this in this article! He also did a test on ABLR's and found that they were off a tad as well! Here is a list of the ABLR's that he tested and the differences that he found in published Bc's vs actual BC's !

i talked to a Ballistician but forgot where I called and was told they were fixing to use a Doppler radar to,actually measure the projectile vs a static calculation is what I was told? Hope this makes a little cents

 

[Ridgerunner665]

In the past...I've given Nosler a pretty hard time over their advertised BC's being off by a good bit...now that I know more than I did then...I'd like to apologize for that, I was out of line.

I still say they could do more to get us some usable numbers...but until the last few years the market didn't really demand it...however, now that more shooters are more keenly aware of BC and how it works...if they could provide more detailed data (a la Sierra) it would be very helpful.

I know providing an accurate BC is trying to hit a moving target...it varies by velocity and twist rate, and rate of spin (actual rpm's the bullet is spinning) varies by muzzle velocity...so the only way to get even a reasonably accurate number is by doing it the way Sierra does...testing at different velocities in standard for caliber twist rates.

Most die hards know by now how to figure out the BC in their rifles...but more accurate numbers "on the box" would likely be of great help to the "not so die hards" who are just getting started.

Just a thought...and an apology for being an ***.

 

[Vince]

Never thought you were a you know what.
You bring up a valid point and one I feel needs to be addressed. I'm not shooting far enough yet that it matters much but it will soon. I use the published BC data as an approximation and refine it further by measuring my bullet drop at various distances.

Sent from my SGH-M919 using Tapatalk

 

[Ridgerunner665]

Never thought you were a you know what.

I've given them a pretty hard time over it in the past...nothing drastic or outright rude, but "pointed" a couple of times.

 

[Vince]

Nothing wrong with that.

Sent from my SGH-M919 using Tapatalk

 

[FOTIS]

Here is another one. This one the 180 TSX