Even the 180 Accu-Tip or Bronze point should make it through the ribs on an elk. At 50 yards you do tend to have less penetration than you do at further distance, but should still be enough. About the only thing I've ever heard of stopping the original Core-Lokt's has been very large necks like Moose and the Big bear at close range.
As a guide the Core-Lokt was one of my strongest recommendations for loads out of the 308 and 30-06. I can not remember a single animals taken with the Core-Lokt that we ever had to track. Though we did limit hunters to shots under 400 yards.
Maybe you got one of those worthless controlled recoil rounds by accident
I know a few fathers that got suckered into that stuff for their young kids. Ended up being horrible performance on game. Though in each of those cases it was more of a 30 cal FMJ entrance and exit rather than a bullet stop outside the cavity.
Everyone has their favorite stuff. Few are absolutely right or wrong in every single situation. I am a fan of the Nosler loads too. Other than my 257 Roberts all my guns love the stuff. Though most of my guns shoot the Core-Lokts, Winchester Blue box and Federal Premium extremely well too! About the only bullet I truly hate, due to poor experiences, has been light bodied animals with the heavy bullet weight Barnes TSX from slow muzzle velocity guns and the .270 130 grain Partition. But others on this forum seem to love them so
Someone seems to have a horror story with just about every bullet out there, it seems. Usually a "right bullet/wrong scenario" most of the time. But failures do happen. Sounds like Rooster had a bad one for sure! I'd bet the next 19 rounds in that box would drop that elk in it's tracks. Good thing there are lots of good alternatives out there...until the next failure
Back to the OP. As far as practicing is concerned I guess I would have to ask, "What kind of practicing will you be doing?" If all you are doing is working on fundamentals and recoil awareness I can not see where one brand of ammunition would differ from another. Although, if you are practicing to work on the best possible scope setting, grouping with your chosen hunting rounds and mapping DOPE? I'd definitely do all that with the rounds you intend to hunt with. Be that Nosler, Remington, Winchester or Joe Magillicutty's Magnificent Blood Splatters'.