I'm making final preparations for my trip to Colorado and the guide suggest a good sleeping bag. We will be in a 'bunk house' but it is very primitive. Who knows sleeping bags and can point me in the right direction?

I know that they are rated. Here's a link that may help you decide.
http://www.bigskyfishing.com/camping-gear/sleeping-bag-temperature-ratings.php

Pay no attention to the high dollar bags they're advertising.

Big Agnes, Synthetic fill, -25' rating or thereabouts. You may get away with a bag with a higher temp rating, but I would err on the side of being rated for cooler than warmer.

I have an army mummy bag that I've used in some cold weather and have always stayed warm. You could probably find one at an army surplus store or on Craigslist.

If you want to borrow one, I have a wiggy's -60F that can't be beat.

I have a Marmot Hydrogen. It's a 30 degree bag. I sleep hot, but I could add a liner to increase the rating. If you have to pack your stuff in, you'll want a down-filled bag. If you're on a horse, then synthetic will be fine. Just remember, the lighter a piece of hiking/camping equipment is, the more it will cost. This time of year, I would go with at least a zero degree bag. It all boils down to if you are a hot or cold sleeper.

You'd be surprised at how hard them things are to find anymore. I've got one also and wouldn't take anything for it.

Cheap and you will keep you warm or make you sweat till under freezing...

Down looses it insulating properties when wet, and is slow to dry,but packs up very small, which is an important consideration when buying.

I also have a Big Agnes insulated air core sleeping pad.

I've got a wiggys also that you can borrow if my wife can find it. Damn fine bags made in USA.

Wiggys

Matters the use for the trip and what you may use it for in the future. How cold will it be in the bunk house? Will it get wet on the way or inside the bunk house?

Most sleepings bags that are for backpacking and such will be great but the temp rating and fill may prove to be important.

I doubt you will need a bag rated -25 in a bunk house but call them and ask them. Do you plan on using it camping here in bama on a 15-20 degree or lower night? If not then you can get by with O to +20.

Fill is important. Down is usually best but if it gets wet its worthless. A little snow ain't gonna get it wet on the way to the bunk house if packed well. Synthetic has come a long way and is still warm if it gets wet.....but it ain't down.

The temp ratings are not absolute. I've about froze to death (not literally but damn sure uncomfortable) at or 5 degrees above both 0 and +20 bags. So if they were to say hey, it will get to 5 degrees in the bunk house (not likely), then -20 degree rated bag would be the ticket.

Good bags include but by are no means limited to: Kelty, Marmot, Mammutt, North Face, Big Agnes, Sierra Designs, Mountain Hardwear, ect. Store brands like REI are decent too for someone who isn't going to use it 30+ nights a year.

Call and get some intel on the bunk house situation, as in heated or not!

Just my opinion......but I usually do spend 30+ nights a year in a sleeping bag, in many different environments, in many states.

Sleep in your underwear or naked. Sweating will equate to a bad experience. Since you have a shelter available, you can get away with a warmer bag, IMO. If you are hoofing it in, weight will be a consideration. I have hunted a few times up around 10-13K feet. It was beautiful but a ton of work.

Good luck brother!

I got one of the brown Canvas Coleman bags at Bass Pro a few years back that will flat cook you if its above freezing.

Check out the "Slumberjack" brand lineup.

This is a top secret secret, so don't tell anyone.

The best place to buy a sleeping bag is unclaimed baggage....

The temperature rating on a sleeping bag is the temperature at which you will die from hypothermia, not the comfort rating.

I never liked mummy bags because I sleep on my stomach. That was until I got an XL bag that North Face makes. I don't remember the name of the bag, but I love it. I think it's a Goliath but that might not be right.

Wiggys are the bear bags made...... Period. They are pricey though. If you want a bag for the rest of your life for any and all circumstances, buy a wiggys. Or borrow one of the two that has been offered.

I spent the last three months in Alaska most of which was on a tent. I used a wiggys for some of that time and an Alaskan guide series bag for he rest. The cabelas guide series bags are very tough to bear for the price.

I took a Big Agnes "Hog Park" +20' bag to Ak.
10 nights in late Sept./Oct. out of Bethel.
I dont know how cold it was but it was cold w/snow,ice,sleet.
I never got cold in my bag.
Good Bag. Roomy.

North face dolomite 0° rectangle bag is a good mid price option. Since you are not backpacking, weight isn't an issue so look at the Alaska guide models too. If you like to spread out, rethink a mummy bag.

Wiggy, big Agnes, marmut are great bags, but more money.

Goose down army issue bag.