I have been using an 8mm ultra-mag for 3 years now. I love it!! Dies were from RCBS and were about $150 if I remember. I am using both 7mm and 300 brass, both are a run through the sizer die and load,no different than reloading for anything else. I am getting 3300 fps out of 200's Accubonds and Matchkings.
I have lived in North Idaho all my 44 years and hunted since I was 12. I have had the 7mm's. They kill elk but not nearly as good as a 300 does. The 300's do well but not as good as the 8mms. What I like out of the 8mms is they kill so very well and all with the recoil of the 300's.
I build my own rifles so have had just about everything. You do not need more than a 200 grain bullet for an elk no matter the shot. A 200 in either the 30 cal. or 8mm will break all apposing bones and get the job done.
I used to hunt with a 378 weatherby until I shot the barrel out. I rebarreled to a 416 Weatherby improved. It was much fun. That rifle is now a target rifle in 500 A-Square with a super match barrel from Pac-Nor. I am getting 2400 fps out of 750 grain A-Max's. For energy at long range only the 50 bmg really does much better. Remember the buffalo hunters used to make incredible shots out past 1000 yds with the Sharps.
I have used the 338's, all of them. I only mentioned this to help those who question what I am about to say understand that this statement is not made from a fear of recoil. I have sat on the bench with a 10 lb 378 (no brake)for over 80 shots a session shooting at over 1000 yds more times than I can remember. I pulled the same stunt with the 416 getting 2900 fps out of 400 grain bullets(also no brake,11 lb
I will say the 500 needs a brake for any fine long range shooting.
The difference between the 8mm and the 30 on elk is very noticeable. I find that the bullets I am using (accubond and matchking,also the 220 sierra) are the ones I would use even if there were more bullets available. The 338's are OK but most guy's need a brake to use them where if you are already comfortable with the 30 cal you would only notice how much better the animal was hit with the 8mm. As far as hitting at long range with any of them? Most people are just going to put on the scope with the target knobs and dial it in.
I find it heartening to see other people trying new cartridges and calibers. I would never tell anyone not to try something they thought would be neat,TRY IT!!!! Without this concept we would still be using the Krag. Remember,it still kills them dead.
You can get used to anything if you go shoot it enough.