Yeah that was my first guess Daryl. I have had horrible results with the Speer 270 grain in my 9.3X74R even on small deer. It's a big varmint bullet for sure. Super accurate, but the worst kind of bullet that can be made for big game.
Speer doesn't care either, and is pretty up-front is saying so if you write to them about it. I know, because I did.

And Texas John, you experience is very similar to mine. I started out with a 300 Savage and went to a 270 when I was very young. I started doing gunsmithing in my teens and I have done it for many many years now. About 1/2 a century. I can have any caliber I want for the same price, because the labor is "free" to me. And believe me, I have done it. I have made and owned a LOT of different calibers and I killed game with them all. I have to say I have seen more killed on game than I can count and when I compare good bullets to good bullets, I have not been able to see any real difference in how more powerful rifles have killed elk any faster than my 270, and the truth is many of them were not AS FAST as the 270
I can only speculate as to why. If I had seen it 3-4 times I might explain it away as "luck", but I have seen it probably 40 times on elk, at least 250 times on deer and maybe 45 times on pronghorns. Throw in a few moose 1 Bison, about 15 big horn sheep and 3 goats as well as a few bear and about 25 horses and cattle on the ranch. That's not luck.

What is it? I don't know for sure, but I can say without any reservations at all the 270 will kill well past it's supposed power level and it's been doing so for about 80 years.
Anytime theory and facts disagree it's easy to guess which one is wrong.
The 270 stands of facts.

Yes there are failures, as there are with any caliber loaded with bullets that break up. It has nothing to do with the brass powder bottle we call a "caliber". I have seen in in "buffalo rifles" and so have others. Daryl and I both have had such experience with 270grain .366 bullets fired from guns WAY more powerful than a 270. I have seen it probably 12-14 times from various 300 magnums and about 10 times from 7MM mags as well as a few dramatic failures from a 338 magnum. All were bullet failures, not "caliber failures".

But when we compare apples to apples, and good bullet to good bullet, the 270 needs no apologies at all.