gwmican,
You might/will want to slug your bore before deciding on what diameter conical to shoot. The knight bore diameters can range from .500" to .5035" from just the few I know about lately. I just bought 3 Knights of the same make and model (Disc Extreme MHC) and all 3 have different diameters. I used .503" No Excuses to check the land to land bore measurements.
.501" = started with fairly hard pressure (not good)
.5015" = started with moderate pressure (acceptable)
.502" = started with light pressure (perfect IMO for a .503")
A .504" bullet would have been a real bear in the .501" bore. Of course if you order from Bullshop, you can have them sized to whatever your bore prefers.
Knights specs are .500"-.502", but we all know that most barrels run on the high side of that and over. I would say the majority run in between .501"-.502" as in my examples. UC had a KRB7 with a tight bore, but just got a new barrel with a .503" bore IIRC. His KP1 has a .5035" bore.
If you know your bore diameter, it will save you alot of time and money finding the proper conical. Either the 445 gr UC Shorts or the 460 gr NEx from Bullshop, or 460 gr No Excuses should be perfect for Colorado Elk. I use 80 grains of FFFG 777, .518" x .060" fiber gasket wad under my .503" diameter bullets in my .502" NEF Huntsman (Green Mountain 1-28" barrel, same rifling as Knight).
Remember Colorado has a limit on bullet length, no longer than twice the diameter, or basicaly 1" for a .50 caliber. If you want to get technical, a .504" White could go with a 1.008" bullet. The 460 No Excuses/460 NEx Bullshop are around .970" or a little under.
Don't use a PowerBelt, trust me on this one. To make a long story short...my buddy shot a huge 6x6 at 28 yards and the PowerBelt blew up on the shoulder...tracked for over 3/4 mile...looked for 2 days...came home sick...still sick! I shot mine in the exact same place (opposite shoulder) a couple days earlier with a 430 gr White Super Slug (obsolite) at 46 yards, went 56 yards and was DOA. The solid lead slug plowed through the shoulder, taking out the heart and lungs. The problem with PowerBelts are the deep hollow point, it is the same on all the bullets, so the ones under 400 grains are to light and explosive, the ones over 400 grains are too long for Colorado. Save yourself the headache, don't use them on ELK!
Hornady is making a new bullet, the FPB. This bullet is a 350 grain skirtless bullet that is supposed to load like a powerbelt, that may show some promise. I have not seen the length of it posted anywhere as of yet, so it may or may not qualify for CO. Any bullet would be better than the PB IMO.
Good luck on the draw, if you have never been to Colorado in September before, you are in for a REAL TREAT!