I wouldn't say it's the "Last Word" in protection. It beats the rifle leaning against the woodpile or otherwise not ready for immediate use.
The right bullet goes a long way towards being sufficient, Hardcast being your friend.
I watched a video of a guy testing a .45-70 for penetration. I don't remember the exact figures, but he tried two loads with the same bullet, one at 1800(?) fps, the other possibly around 1300(?) fps.
The slower bullet far out-penetrated the faster one.
That's normal. Sometimes.
A soft bullet that expands, will expand more at higher speeds.
Expanding absorbs energy, a wider bullet is harder to push.
Less penetration, bigger wound channel.
A hard bullet that holds its shape will use 100% of its energy
penetrating. And go deeper, if driven faster.
Then you run into the modern "Trick" bullets.
Controlled expansion, partitions, tapered jackets, mono, bonded,
petals that fold back/break off...
combinations of them?
They each have their own rules.
