Let me ask the PUNDITS of the Campfire Ballistic Police Association (CBPA) what really matters in a mattering way.
If one mentions Foot Pounds Energy the CBPA says the FPE figures don't matter.
If one mentions Momentum the CBPA says Momentum doesn't matter.
If one mentions Taylor Knockout Value the CBPA says TKV doesn't matter.
If one mentions Meplat diameter the CBPA says it doesn't matter.
If one mentions a hard alloy the CBPA says to use medium hard.
If one mentions a medium hard alloy the CBPA says to use hard.
If one mentions a Soft Alloy the CBPA says to use medium.
If one mentions A2400 the CBPA says to use H110.
If one mentions Unique the CBPA says to use Powerpistol.
If one mentions Alliant Bullseye the CBPA says to use Red Dot.

I could go on and on since I am retired and just twittle my thumbs but I am absolutely sure as smart as the CBPA is they get my drift.
Unless maybe they aren't.

SO WHAT DOES REALLY MATTER IN BALLISTICS?

Sig line

what did John Taylor kill a bunch of elephants with? .257 Rigby?

.275 Rigby aka 7x57 Mauser.

Don't you mean Bell