The 180 grain Hornady GMX or the 200 grain Nosler Partition are both good.

I killed a nice bull with 170 grain SSTs 3 years ago and I will not try it again on elk. Good for deer, but penetration was less then I like and one of the bullets came apart leaving only the jacket and penetrating only about 14".

I have used the 200 grain Partition with perfect results in the past and so I will likely go back to that in the future but I put together some loads with the GMX and they shoot under MOA so I am confident they would do fine too, despite the fact I have never killed an elk with one of them. They shoot a bit flatter, and with 95 to 100% weight retention, I feel confident in saying they will go through too. Complete penetration with an exit is my goal and weight retention is one way to gain penetration, but if I get a good wound channel of reasonable diameter and an exit in a fairly straight line, I am satisfied with the load.

My 8X57 is a full-stocked carbine and with only an 19" barrel I give up a bit of velocity. My best loads shoot super well, but most times they are not "red-hot" and the rifle seems to shoot it's best at about 2400-2500. But with 180 and 200 grain bullets.

I find the 200 grain Speer shoots to the same point of impact and is just as accurate as the 200 grain Nosler, and that is my main reason for choosing the Nosler 200 gr Partition as my hunting bullet. I shoot the Speer, sometimes up to 1000 per year, as a practice round and then I need only buy 1 box of Partitions for killing game. This is typical of the accuracy I get from both the Speer and the Nosler.
[Linked Image]PC070001 by .com/photos/156296479N08/]Steve Zihn, on [bleep]
[Linked Image]PC070002 by .com/photos/156296479N08/]Steve Zihn, on [bleep]
I have found the Speer to be very prone to come apart too, which on deer and antelope is not a big deal because even when it comes apart it's still large enough to exit.
Here is a picture of one of them sectioned to show the jacket thickness. It's next to a 270 Remington bullet made in the 1970s
[Linked Image]PA130001 by .com/photos/156296479N08/]Steve Zihn, on [bleep]

However I get a lot less fragments and ruined meat with the Partitions, so I'd even stick with them for hunting small deer just because I don't need to use anything else. I can do all my practice with the Speers and just shoot Noslers for game. I had an 8X57 which I used when I was in my 20s and for some (dumb) reason I let it go, but I did kill several head of game with it. I made the short barreled carbine for myself about 6 years ago, and have killed deer, antelope and elk with it too.

40 years ago I used some 185 grain Remington Core-Lokts and they did very well for me, but Remington has stopped selling them, so I am back to the 200 grain Partitions.
As I said, I have full confidence in the 180 grain GMX too, but that is just from tests in saturated news paper with cow bones. So far I have not killed an elk with one.