I gotta say that for me sectional density does not mean a real lot.
In reality SD is only related to two things, bullet diameter and bullet weight.
SD tells nothing about bullet construction and it does not even tell anything about the bullet shape.
Also the SD number or value cannot be counted on to give an indication of the relationship of the length of a bullet compared to its diameter when looking at different caliber bullets even when they are constructed in similar ways.

For example, if a bullet in a certain caliber had a SD of say .331 and was long in relation to its diameter it is often assumed that a bullet in another caliber with similar SD value should have a somewhat similar diameter to weight relationship provided both bullets were constructed in a similar way.

This is NOT the case however!
To prove the point take a look at a (Woodleigh) 220 grain .308 cal full metal jacket "solid".
The sectional density of this bullet will be .331.
This is a very LONG for caliber bullet where the length is four and a half times the diameter.
Now look at a (Woodleigh) 900 grain 600 NE solid.
This is a very SHORT bullet where the length is only approx two times the diameter.
These are two very different bullets where the 220/.308 is very long for caliber and the 900/.620 (600NE) is very short for caliber.
But guess what.
Their Sectional densities are almost identical!
The 220 grainer has a SD of .331 and the 900 grainer has a SD of .334!
hmmmmm