People need to remember, a .284" 160gr and a .308 160gr or 165gr are NOT the same.

A smaller bore has more friction. But an equal weight bullet better penetratration, ceterus parabus, and a better potential ballistic coefficient.

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Also I have trouble understanding shooter logic. If "modern" powders can improve some cartridges so much why a belt on the outside of a cartridge means an often larger capacity case can't also be improved in velocity similarly?

In addition the Gun hack writers rave on about modern cartridges fat, short, straight walled being "efficient".

I have a real problem with unsupported by any actual objective and independent evidence scientific claims.

Like the "bubble" which allegedly forms in front of a meplat flat bullet IN FLESH .... A bubble may well form in flight in gas, is air. Does not mean a "bubble" in a solid ie flesh occurs. Independent objective evidence? Always lacking. Sure some ballistic gel test by the seller or hack. But one result? Perhaps the best only shown. From the maker I'd want to see TEN comparative gel tests. By an verified independent tester.

Same with cartridge efficiency. Sure a short fat cartridge MIGHT burn the powder better? But it might not. Long and thin might with reasonable width. We are talking about fire here. Compressed thick often burns lesser?

If short straight fat IS more efficient .... And just because hacks repeat it endlessly does not make it true. Remember how once "one had to have a cartridge with a magnum belt!". Then " only a rimless cartridge is good, not those magnum belts". Then it became "only straight wall and fatbonly". Pfffffft!

Myself I KNOW a sloping sided cartridge like an Nitro Express or Vintage cartridge EXTRACTS better. A SUPERIOR characteristic for a dangerous game cartrudge used in hot or tropical climates. My guess, also for icy frigid climates ...

Whenever I see 2+2=5. I get distrustful.

If there is more efficiency, what is the increase 0.5%, 1%, 5%, 20%? I think any efficiency increase is very minor. And largely irrelevant.

To test I would want to see two cartridges, equal bore, same bullet, equal powder, same powder capacity. Same barrels, twist, length in front of the chamber. One cartridge longer, thinner, more sloping. The other short, straight walked, fat. What is the velocity difference? Is there any way to test unburned powder? 100 shots from each test.

If a .30-06 can be souped up, I'm sure a 7mm Rem Mag can be as well.