Go with a 50 caliber muzzleloader, it is basically the standard, and has the most bullets and accessories available, and is a great elk and deer caliber.
I believe the best "multi-state muzzleloader" is the Knight Disc Extreme since it can be equipped with the optional "western" kit to hunt states that require open ignition and musket or percussion caps. it is a bolt style rifle, so there are more parts to deal with when cleaning. The advantage being you can muzzleloader hunt in nearly all western states with this muzzleloader.
For Colorado only, I do not believe you have these restrictions. The most simple and reliable muzzleloaders I would go with a break action muzzleloader. They are by far the easiest to clean and maintain. They are light and fast handling. I like the CVA Accura, it is a super muzzleloader. I have heard that Thompson Center also makes a great break action rifles.
Since you need to use open sights, I would go with the Williams FP peep sights for the rear sight and the XS Sights white line "partridge" front sight. With this front sight there is a fine white line that is easy to pick up in various lighting conditions. You also do not cover your aiming point with this sight. Bead type front sights can cover a considerable amount of the target at 100 yards. I typically only lose 1" of accuracy at 100 yards shooting this sight set-up at 100 yards versus a scoped muzzleloader. I don't like fiber optic front sights since they have the problems of a bead type sight and can be difficult to use in certain lighting.
For powder, Blackhorn 209 is the leading powder by far. Typically 80 to 120 grains by volume.
For 209 primers, Fiocchi makes a great primer. There is a balance of properly igniting your powder properly and the primer having too much oomph that it unseats the bullet off the powder before the powder ignites. Fiocchi's usually work great.
For bullest go with No Excuses 460 grain pure lead bullet (50 cents a bullet), or the Thor all copper bullet.
The No Excuses can be ordered on-line. The heavy bullet will retain energy well at extended range. Also the heavy long bullet stabilizes well and is typically the most accurate in most of today's muzzleloaders. Since most muzzleloaders have a fast twist shallow rifled barrel designed to shoot sabots (illegal in Colorado), a long heavy bullet typically is the most accurate out of these sabot barrels. The No-Excuses is also a die sized "slip fit" bullet and pre greased, so they are easy to load.
The Thor is a Barnes copper style bullet and you need to order the exact bullet size for your specific gun. Call Thor and get a test pack to determine the exact size you need. They come in 0.001" increments to insure you find the correct fit for your specific rifle.
With practice you should be shooting 100-150 yards. Accomplished open sight shooters are occasionally effective to 200 yards.
For practice, I personally have equipped a Ruger 10/22 with the same sights as my muzzleloader so I can shoot hundreds of shots with the same sight picture.
I too am thinking of burning 22 points on a Colorado muzzy elk hunt this fall!
Here are a few of the websites:
http://www.knightrifles.com
http://www.muzzleloading-bullets.com
http://www.xssights.com
http://www.thorbullets.com
http://www.blackhorn209.com
