A 30 cal is hardly a smaller caliber.
The .308 is more than enough for any elk. This last weekend, while out in the mountains with my elderly father the topic came up about how many elk we had taken in the region (we had no idea, but it was a bunch). Then the topic went to what we used rifle wise, and I had used a .308 for the vast majority of them. From one singe 50ish yard snap shot, to a 615 yard shot, they all fell over dead. The average shot (for me) was in the 400s. Not by choice, but due to environment/terrain.
I would suggest a 155 Scenar pushed by Varget .
You don't need premium bullets BTW, but if it makes you happy, go for it. Before I switched to 155 Scenars, I used Sierra 165 grain hollow point Game Kings, and they were absolutely deadly on mule deer and elk. The reason I switched was that past 5-600 yards the 165 HPGKs started to really get blown around by the wind, due to their profile, whereas the Scenars shot tight groups at all ranges. I never had any intention of shooting at the longer ranges, but the Scenars external and terminal performance was hard to ignore.
If your buddy can shoot, then he will not have any issue. Killing elk is not very hard. Getting them back to the truck is the hard part.
