168g VLD on elk at 300 RUM speeds is definately not the bullets fault...You should have been using the 190g at least like you said, and even better yet, the 210g...If you notice around here, no one uses anything less then the 190g VLD's out of the 300 RUM for deer/elk, theres a reason for it. Poor decision on your part to use basically a varmint bullet at those speeds on elk.
I had great success with my 300 RUM using the 210g VLD and 88-89g H-1000. Using Rem cases, Fed 215 primer, seated to touch the lands. Velocity was right at 3K, and accuracy was 1/2-3/4 MOA to 800 yards.
I never did shoot any deer/elk/bear with the 210 VLD's, only a couple very unlucky coyotes, rocks, and steel. They are a very frangible bullet and really not meant for penetration. They are designed to fragment and explode inside the cavity. This can be good or bad, depends on how far and where you hit the animal. Depends on if you want 2 holes or not I guess. For elk/bear, I"d use 200g AB's and thats exactly what I did after shooting a 450lb black bear at about 200-250 yards with a 200g SMK at 3200fps. Bullet entered behind shoulder and was found on the offside shoulder. All I found was a tiny piece of jacket that weighed about 30g. Sure the bear died within 10 yards and no follow up shot was needed, but based on that performance alone, I was not about to use them on elk. I switched to 200g AB's at 3200fps and never looked back for killing animals. I took a few elk with the 200g AB and it smashed through cow's and spike bulls shoulders leaving baseball size exit holes and a blood trail stevie wonder could follow. Except there was no tracking to be done as they all hit the ground instantly with shoulder shots.
Bergers just seem to be either to explosive, or they pencil through.
I have used the 7mm 168g and 180g in a 7 RM on deer and have had mixed results. The first year I used the 168's at 2950 and took a buck at 618 yards. Bullet entered the shoulder and blew up badly. The buck ran down hill and a follow up shot was needed. Upon examination, the 1st shot barely got through the shoulder bone and didn't reach the vitals, this was at 600+ yards mind you!! The next year I decided to use the 180g VLD thinking the heavier bullet would be little tougher built and penetrate a little better. I had these loaded to 2825fps and I shot a buck through the shoulders at 100 yards and he stood there like he just hadn't been hit with over 3000 lbs of energy. He should have dropped at the shot, but instead he just stood there and walked a few yards and looked at me. The 2nd shot I put behind the shoulder and he fell over dead.
Using milk jugs filled with water will give you a good idea of what to expect as well, at least from my experience. WIth the 168's, they would vaporize the jugs out to as far as I could hit them. With the 180's they acted like FMJ's and had absolutely no POP what so ever to the jugs. That performance was identical to what I saw on my deer that I shot.
Based on these experiences, I am pretty much done using target bullets for game, save the 300g SMK out of my 338 EDGE.
For long range deer, I look no further then the Nosler Ballistic Tip. I haven't found a bullet yet. For elk/bear, the AB is tought to beat for repeated terminal performance.
Hope this is of some help.