I've seen two elk killed with a .257 weatherby using 100 grain barnes tsx. One was maybe 175 yards, the other much closer. Both one shot kills, both hit behind the shoulder. Both made it about 20-30 yards, both bullets shot clear through, breaking a shoulder in one case, just ribs on the other. I also saw a friend shoot a mature oryx with the same 100 gr tsx and same thing...dead oryx, that one didn't take but a couple steps.
I've seen I cant tell you how many pronghorn killed with a 257 weatherby. I have friends from AZ that shoot that round a lot, and for everything they hunt. They have been coming here to hunt for 15-16 years straight, and usually kill 2 or 3 pronghorn each.
The argument that you need a .30 caliber or bigger for elk is all hogwash. Certainly nothing wrong with a .30 caliber, but we live in a great time for bullets, brass, powders, rifles, etc. etc.
When I killed my first elk in 1980, I would have agreed that a 30/06 or better was the best choice. Even then, the partition and a few other bullets were quickly going to level the playing field.
As far as shot selection and worrying about penetration on quartering shots...a crap bullet in a .30 wont penetrate as well as a smaller caliber with a controlled expansion bullet.
Heres a few elk killed with the 7-08 and 140 accubond...I've seen 18 elk killed with my rifle and recovered 2 bullets on shots from 50 yards to 625, from all kinds of angles.
Shot this one hard quartering away about 30 seconds after I punched a cow behind the shoulder...bullet entered in the back 1/3rd of the rib cage, exited the point of the off shoulder:
Tight behind the shoulder on the cow, 30 seconds prior:
Cow entrance side:
Exit, about ideal IMO/E:
Out of 71 elk I've killed, this is the only one that I've broken both shoulders on. Bullet exited at 210 yards:
Have to admit, I was a bit worried shooting this bull hard quartering at 70 yards with the 140 AB and 7-08. Not sure what I was worried about, broke the on shoulder and exited the back of the rib cage. Bull left a short, but copious, blood trail that any amateur could follow. You can see the exit on the bulls side toward the back of the ribcage:
Bull my brother killed with my 7-08 485 yards hit him about the middle of the ribcage on the on-side as it was quartering a fair bit. Recovered the bullet on the off side, and broken shoulder just under the hide. One of the 2 140 grain AB's I've recovered from my 7-08. Entrance side facing camera (small blood spot on the hide):
Recovered bullet from that bull: