I will NEVER shoot another animal with Sierra bullets out of my .303 again. Shot a mulie this year three times with 180 grain Sierra handloads - the deer died (I hit him good all three times), but almost zero bullet expansion that I could tell. I wasn't at all happy during the post mortem.
Prior to that little adventure in handloading, The Wife(tm) and I both have been shooting everything (deer, elk, bear, grouse, etc) with Winchester 180 grain PowerPoint's. Everything we've ever shot with those died in short order, and the only bullet we ever recovered (center-punched two ribs and a shoulder on an elk and hung up in the hide on the far side) was a mushroom approx twice the original diameter, and about 160 grains of retained weight.
I give two thumbs WAY up for the Winchester PowerPoint's in the 303 British. I'd expect any elk close enough for you to hit him in the vitals would be dead in short order if shot with that load.