I found great wisdom in the above replies. I have a 300 weatherby mag in a vanguard action. Built it up with a lilja mark 13 barrel, McMillan A5 stock, CDI bottom metal with AICS box mag. IOR Valada scope. Lots learned during and after the build. I have always wanted a 300 weatherby since I was 10 and read about it in Field and Stream so I got one at the age of 29 love my rifle. What I learned converting this bone stock vanguard to more or a tactical type of rifle which I carry with me every deer season and shoot out to 1350 yards so far on steel is this. I can't load some long heavy for caliber bullets because of the COAL compared to action inlet leinght. This got some what better by a .150 when I went to CDI system and now can load out to 3.695 and still have reliable feeding i can go to 3.720 but the cartridge hangs on the ramp so not good for hunting. To load some of the 210's plus it pushes me back into the powder column and some VLD styles have the ogive into the neck. That is the main problem I have with the action which I can have the feed ramp milled back a bit and get some of the AICS 3.800 ish boxes and get into the heavier VLD's. This will cost more money and questionably weakens the action. I would rather buy a new action in time.
With all that said on my experience, look into a cartridge that will fit your action inlet and get a detachable box system from CDI it coast 400 for the bottom metal and two AICS boxes you can go cheaper with magpul. This will give you all the room you can have for the action you have, plus CDI will inlet your stock for free. Look at the ballistics like Applied Ballistics or JBM great stuff and run the numbers for said cartridge with different weight and style bullets you may find as I have a heavy long VLD for caliber may only give you better wind and energy down range than a mid weight hybrid will, and only marginally better at that. So you may not have to fight with long COAL that requires special attention and frustration.
If it were me wanting to shoot elk at 500 to 600 yards and have fun shooting steel I would stay around .30 cal to 7mm you have energy down range this will help in the hunting world as a near heart shot needs the extra knock down as well as the heavy front shoulder bone. We all know that animals don't stay still and it only takes the flight time of your round to take a perfectly executed heart or double lung shot to turn into a direct sholder bone, liver, neck etc. I like my horse power and it never fails.
As mentioned by another pick your favorite cartridge and caliber keep it real with the hunting aspect use the ballistics app's and look at your action you can always rebarrel and have a gun smith cut the chamber to precision. PS you can shot steel and paper with a .22Lr but not elk just saying.
Sorry so long of a post.
