Nosler Folks - Your .270 BCs

[Lou270]

Nosler Team,

One thing I have been curious about is why your .270 bullets generally have lower BC than bullets of 7mm given same bullet weight or .308 of slightly lower SD. For example, the 7mm 140 Partition and BT have higher BC than the .270 equivalent and the 150 and 180 .30 Cal have higher listed BCs than 130/150 .270 bullets, even though the 270 are a bit higher SD. Was this an intentional design move or some other reason? Just curious as I noted that on AccuBond the .270 140 is higher than the 7mm and that for pretty much every other manufacturer, the relationship between SD and BC is evident (i.e. higher the SD, generally higher the BC - so a 130/150 .270 is generally higher BC than 150/180 .30 cal and equiv. weight 7mm). It is not something I'm worried about, but something I've noticed and have been curious about.

Thanks,

Lou

 

[WPH]

It seems to me that bullet companies have their own ogive design that seems to have an efficiency peak in certain diameters. Also compare other diameter bullets with the same sectional density, .243, .358, etc. Usually at a point each way you start losing b.c. . 6.5 mm to .338 seem to have the best. 6.5mm and 7mm usually have the highest b.c.

 

[Lou270]

WPH,

Similar statements about the 6.5mm and 7mm usually having the highest BC is what got me curious to go looking around. I have seen several articles in the magazines comparing .277 to 7mm making similar statements (i.e. 7mms have higher BCs) and the most common example used is the Nosler BT. When I went and looked at just about every other bullet maker I could think of, the .270, given similar weight bullets, has a higher BC than 7mm bullets. This is what I would have expected because of the .270s higher SD with same weigh bullets. Nosler BT and Partition in the 140 gr. weight are pretty much the only 2 bullets that show a reversal of this trend and maybe some of gunwriters are cherry-picking data to further their own bias. I was wondering if the BC data for either 7mm or .270 data is incorrect, maybe not apples to apples (for example, Sierra lists BC based on velocity), or design (as you mentioned, maybe Nosler's Ogive design is not optimized for .270).

-Lou

 

[Bigwheels]

I would also like to know how they get thier BC's.I shoot a 338 with 225gr. AB's,& noted that when I put the given information into my Infinity software the results did not add up with field testing.The Nosler bullets dropped more than expected @ all ranges.I have done everything I'm capable of testing on my own(ie. measured MV useing 2 different chrony's,etc.)I have no explanation.

 

[Guest]

Not sure what is going on with the 338's, but the issue for the 7mm is that, for a given weight class of bullet, i.e.-light, middle, and heavy for caliber, the 7mm has about the best BC out there. Yes, a 150gr .277 has a higher BC in some cases, but comparing apples to apples, that bullet compares to a 160gr in 7mm. Consider the light bullets for caliber. In 7mm, light means about 120gr, in .277, the light bullets are 90-100gr. In most situations, in similar cartridges like the 270 and 280, or 270WSM and 7mmWSM, the lightest bullets are going about the same velocity give or take, and the heaviest bullets are also going about the same velocity. The bullets are, for caliber, roughly the same. The difference? The 150gr is moving faster out of a 280 than a 270. So, slightly higher BC gives way to slightly higher velocity, I imagine. Take a look at the comparisons for various load data and see for yourself.

For a more obvious comparison, consider the 100gr .243 bullet's BC compared to a 100gr .277. Still 100gr, but not the same BC. 7mm is, for most ogive designs, the most efficient (highest BC) bullet available per weight for caliber.

 

[remingtonman_25_06]

For size, 6.5 and 7mm have the highest BC's, save except the big .338" 300g bullets. .277' BC's only compare to 7mm in lighter weights in 140- 150g, they dont compare to a 160g or 175g in 7mm, nor does it compare to a 140-142g 6.5"

 

[Lou270]

For a more obvious comparison, consider the 100gr .243 bullet's BC compared to a 100gr .277. Still 100gr, but not the same BC. 7mm is, for most ogive designs, the most efficient (highest BC) bullet available per weight for caliber.

I guess this is what I'm trying to figure it out. I agree that 7mm bullets of higher SD (i.e. greater weight, such as 160 and 175gr) will have higher BCs than a .270 of lower SD, but I see no trend anywhere that supports that a 7mm of equivalent SD has a higher BC than a .270 bullet of equivalent SD. I have seen several writers make the comment that 7mms have higher SDs than .270s given the same bullet weight, but the only anomoly I could find was the 140 Nosler BT and Partition, which lead to my original question. Just about everywhere else, whichever caliber was using a bullet weight with a higher SD (given equiv design), the BC was higher, which I would expect.

-Lou

-Lou

 

[Lou270]

I have seen several writers make the comment that 7mms have higher SDs than .270s given the same bullet weight

Meant to say "that 7mms have higher BCs than .270s given the same bullet weight.".

-Lou

 

[Guest]

I haven't checked every bullet on the planet, but I can tell you from my cursory check of six different manufacturers, that my original post is right on. Given a tit-for-tat comparison of bullet weights for each caliber, the 7mm's have a higher BC than just about anything out there. Again, consider that the 130gr .277 is equivalent to the 140gr .284, and go from there. Of course the 150's are not identical in BC, as one is larger in diameter than the other, and thus it has a different BC for the same grain weight, because it is shorter (by definition of it being larger diameter). As for the differences in SD, I can't really speak to that, haven't checked it out, but I know the rule is the heavier a bullet is in a given caliber, the higher the SD, and that's the rule I always use.

 

[Savage99]

Nosler BC's are all over the place.

I use Sierra's data. Thats not only tested but relevant to the velocity. Just match the bullet as best you can to the closest Sierra and then test the impact at the maximum range.