Best four season bag out there. Good to below zero and less than 600 clams if you can...

What's your height, weight, and chest girth?

Down or synthetic?

Where is the intended use (mostly)?

Aside, there is no "best"...

Agree with Brad 100%. If I had to buy one for myself today for under $600, probably Valandre Shocking Blue.

If you are "new" to below zero "camping"...better study up, first.

+1 on the Valandre Shocking Blue.

For $720ish (retail $799.99), looks like a great bag for weight of 3+lbs (normal sized climbers, not little guys) and "comfort rating" of 12F to -3F...

A little spendy and a little heavy for its range.

Many bag makers use the European rating system. With it a 0 degree bag doesn't keep you warm & comfy at 0. It keeps you alive at 0. Be sure of what system they use.

Shocking Blue regular size is $600 at EverestGear. I've pushed it's lighter brother, the Mirage, to single digits and got sleep. The design is good to go. Different cut than WM though, by a lot, it's not for everyone. Slim footbox through the legs, wider at midsection. Best for sleeping on back.

I’ve taken a Shocking Blue down to -10F with a good pad and some minimal layering.

Probably a great bag. The characteristics you noted are not ideal for many. Marmot suits me better for a lower price and weight.

Everest Gear has a great selection of ice tools. Most of their other gear is higher priced than what is available.

Marmot bags, while good are not in the same category as Valendre’, Western Mountaineering, or Feathered Friends.

I'd say a "great selection" of ice tools would consist of more than Stubai and Grivel, but whatever.

Seems like Brad nailed it pretty nicely on first reply.

Anyone tried a Feathered Friends Lark (or a Raven) 10 UL Sleeping Bag?

The last couple CO 1st rifle seasons have been cold

Feathered Friends, Western Mountaineering, and Valandre are all high end bags and it all boils down to personal preference.
Of the three I believe Valandre's quality of construction is the best....but it's not my favorite (WM).
Valandre is geared towards climbers so they are wide through the torso while narrower in the hips and footbox (so not as efficient)....and the exterior fabric is durable as a result of its target users. That said, I used a Valandre Mirage for many years for three season trips in the Sierra and was very happy with it. I only replaced it as since I've become older, I tend to sleep colder and debated between WM and FF and went with the former.

PRM: Feathered Friends tend to be conservatively rated so either bag would work....though you could always have them add overfill when placing the order. Additionally, I'd look at their other fabric choices vs the UL as one might be better suited for colder climates where condensation might be an issue.

Since this is the backpacking forum, have you considered a quilt? Some guys don't like them for real cold weather but I've slept in mine as low as 5 without any problems. The trick is to get one as wide as possible.

I've noticed that the "rated" temps on bags, only means what you should be able to survive in. Not be comfortable in.
Haven't tried these but, there has been some good reviews from people I know that have.

https://www.wiggys.com/by-temperature-rating/

Yeah, they are less expensive, lighter and warmer.

True...didn't see any Black Diamond or Petzl.

Like firearms, one can shoot anything handed to them...if the shooter CAN shoot well.

Same with ice tools, screws, pickets, belay devices,etc. ad infinitum.

I see "snowy" in your name...how are you on water ice, alpine ice?

Past prime, and mediocre at peak. Never led past WI4 and Hyalite WI4 at that.

It's called the ISO (International Standards Organization) rating. It more or less insures that every company using it tests bags the same way so comparisons have some meaning. It still can't account for what the user wears to bed or for how warm individuals sleep, but it's a decent comparison and the most accurate you can likely get.

Was up there years ago, but in summer. Seems like there were some pretty good gullies.

There's 80+ deg angle water ice at Hyalite?? Above Temple Lake? One pitch waterfalls? Wall seeps? Up in the canyon or gully ice? Canyon looks steep in places.

Glad you experienced it.

We have this here every year:

https://bozemanicefest.com/

Dozens and dozens of established routes. The biggest perk of Hyalite is the accessibility of moderate ice. The biggest downside is there are precious few multi-pitch opportunities.

I have one that is rated to 0. It is not a warm bag, and below 20* you will freeze your butt off. It is built well, and is light, and I use it on my sept. hunts,but later in the season I go to a warmer bag.

5 11...190...Never measured but pretty wide shoulder and chest....Down...Montana Wyoming and Utah mostly, and in the mountains. I have camped below 0 lots of times just looking for what works best for others.

It’s a couple hundred bucks more than your target, but I cannot say enough good about the Western Mountaineering Sequoia MF. Proves it’s value late August in the Brooks Range/ANWR. Several nights about 20* and it was toasty, am sure comfortable well below that. Bought it at Hermit Hut in CA, free shipping and free overfill. I’d do it again in a heartbeat.

I have a 20* a 0* and just bought my son a 20* for Christmas. I’ve had my 20* for ten years IIRC, and my 0* for half that. I use the 20* year-round, including winter camping into the 20’s inside a four season tent and on a good pad. I wear thermals to bed (mostly to keep the bag cleaner) and throw whatever outer layer I took off over the leg end of the bag. I sleep toasty, and feel like the rating is honest. The bags are well built and tough, and my only complaint is compressibility. The frameless pack gram weenies would never buy my bags.

I bought the 0* bag on sale for extreme cold, and as a backup loaner in case I could ever talk my aging dad into a basic car camping trip. It’s still unslept in because my 20* is serving me without fault. I also love my Wiggys vest enough that I bought a backup, even though my first one still looks basically new after several years of consistent use.

I’m not a “fan boy,” and don’t know Jerry personally. I just shop hard for the gear that I can afford and that will serve my needs. So far, I’m very happy with what I’ve bought from Wiggys. YMMV.

I have this only in OD green and I think the rain cover is digital i will sell for $100 shipped. This was an issue item but like the one sold here.

https://www.amazon.com/Military-Modular-Sleep-System-Goretex/dp/B002LLPILC