R R - I'm not mad, just tired so this is my last response.
1. You ask how is s d more relevant than weight.
That is the reason you & others don't understand the reality.
The s d is the ratio of dia/length and with the same nose shape, bullets with similar s ds are proportional.
When you compare 130 wt between 264 & 270, you're NOT comparing proportional bullets. (apples/oranges) A 130 264 is more aerodynamic than a 130 270 BUT is COMPARABLE to a 140 270.
2. AS any bullet's s d increases velocity decreases in the same cart. The 6.5 loses TOOO.
3. B Cs are only accurate indicators when used with bullets of similar S D. (comparable)
THUS using 264 120 gr IS comparable to 270 130 gr.
and 264 130 IS comparable to 270 140 gr.
I don't know your reloading background and I'm NOT being critical, but this lack of understanding is the reason you don't understand the REAL relationship between the 260 & 270.
We have writers here on the fire that can explain this better than I. And they do understand.
No hard feelings. I am buying a 6.5X55 and keeping my 270s.
Happy Thanksgiving
I understand completely about sectional density, bullet shapes, aerodynamics, etc. I understand the reasoning behind why one might compare based on SD, but there's no reason to limit the analysis to just bullets with similar SD because there is no law that states we have to shoot bullets with a certain SD. Using a similar SD is one way to compare, but not the only way to compare. Even if you limit yourself to comparing based on SD, 6.5mm bullets have better BCs than comparable .277" bullets with the same SDs (see a thread that someone started this afternoon showing that, based on SD, .277" bullets have lower BCs than 6.5mm and 7mm bullets - there's no denying facts). See also the analysis below. One could use recoil as a basis for comparison, and that's as relevant as SD if recoil is your primary interest. There has even been talk on multiple occasions here at the Campfire that SD isn't relevant in comparing bullets any more given that modern bullets like the Barnes TSX (and other monometals) and the Berger VLD work so differently than the traditional cup-and-core bullets. That's kind of a different topic, but it is relevant to this discussion in that we're no longer bound to using a certain SD bullet for a certain application any more (i.e., bullets with the same SD are not necessarily equivalent any more). You're trying to normalize using SD with the assumption that normalizing with SD will make the BCs essentially equivalent, which you assume will prove your erroneous assertion that a larger case ALWAYS equals more velocity down range by limiting the variables to basically just case size and velocity, which are related. Even using the same SD and bullet design, we'll see below that the blanket assertion is false.
I gave an example of how a bullet from a .260 Rem would have the same velocity at 650 yards as a comparable bullet with the same mass from a .270 Win even though the .260 Rem bullet started 250 fps slower. I disproved your blanket statement with hard data, and you aren't willing to admit your blanket statement was erroneous, as many blanket statements are. You disagreed with the basis for the analysis (using bullets of the same design with the same mass). Here, let's do it your way with SD as equivalent as it can be, and we'll still see that your blanket statement was false.
Elevation = 1000 ft, 22" barrels, realistic loading manual velocities:
.260 Rem 130 gr Berger VLD (SD = 0.266, BC = .552), MV = 2750 fps
.270 Win 140 gr Berger VLD (SD = 0.261, BC = .487), MV - 2900 fps
Velocity @ 650 yds: .260 Rem = 1801 fps, .270 Win = 1804 fps
Wind drift @ 650 yds for 10 mph cross wind: .260 Rem = 29.7"; .270 Win = 32"
Using bullets of the same type with the same SD, the bullet from the .260 Rem has the same velocity as and less wind drift than the bullet from the .270 Win at 650 yards. Not everybody shoots that far, but some people do, and your blanket statement didn't make any qualifiers about only being valid to 300 or 400 yards.
