Quoted:
Just playing around in QuickLoad with this, using 357 Maximum with updated case length, COAL, and making an assumption on H20 case capacity based on 357AR (357 Max Rimless) on the Mad Dog forums, here's what I come up with:

1.710" case length
2.230" COAL
34.5gr H20 fired case capacity
200gr .358 Hornady FTX bullet
55ksi maximum pressure
A max charge of 20.6gr of Winchester 296 powder (Insert standard disclaimer - this is a theoretical load in modeling software for illustration purposes only - do not attempt this at home - reload at your own risk - consult published OEM data for actual loads - start at the starting charge and work your way up)

Results with some common AR barrel lengths:

Barrel Length / FPS
20" / 2,005
16" / 1,938
14.7" / 1,911
12.5" / 1,856
11.5" / 1,827
10.3" / 1,786
8.5" / 1,711
7.5" / 1,658

That's only 150fps drop from 20" down to 12.5" and 350fps drop from a 20" barrel all the way down to 7.5", with a fairly long 200 grain bullet.

Right now - there isn't much in the way of .35cal 200+ grain bullets that will reliably expand at any range in this velocity window. Until someone comes up with something designed with a lower minimum expansion velocity, the 150-180 grain bullets will be your best bet. Which is probably exactly why the Winchester factory loads for launch are in that window, except for the subsonic load.

But, imagine if Nosler was to come out with an 200+ grain Accubond Long Range .35 caliber bullet that expanded down to 1,300fps like they offer in other calibers. We'll be hunting with heavy-for-caliber bullets out to 200 yards with 7.5" barrels and getting reliable expansion!

Right now - best heavy hunting handload in Quickload I can come up with is the Hawk 200gr flat point with a .025" jacket. Not sure what the expansion threshold is on that bullet, but it's the thinnest jacket Hawk offers so should offer more room on the low-end. Taking a wild-ass guess at seating depth and using an 10.3" barrel, it's still pushing almost 1,850fps at the muzzle.

I think I'm gonna have to build one of these!

Edit - A load with the Hawk 180gr Flat Point with .025" jacket could be pushing just shy of 2,000fps from an 11.5" barrel. That may be a better sweet spot hunting load.

Quoted:
Will be trying one of these.

Two main challenges to it killing 300blk: magazines and 30 cal cans.

Quoted:
Will be trying one of these.

Two main challenges to it killing 300blk: magazines and 30 cal cans.

Quoted:
Counterpoint:

The 350 Legend should significantly outperform the terminal ballistics of .300blk, especially at subsonic velocities, and depending upon the pressures involved, there's a good chance that it will work with 9mm and .45 cans.

Quoted:
Counterpoint:

The 350 Legend should significantly outperform the terminal ballistics of .300blk, especially at subsonic velocities, and depending upon the pressures involved, there's a good chance that it will work with 9mm and .45 cans.

Quoted:
That's not really a counterpoint to the fact that magazines won't be nearly as easy as mags for 300blk, and 350L won't work with almost all 30 cal cans.

I agree it should outperform 300blk, especially subsonic.  But people with only a 30cal can won't flock to this, and expensive mags will stunt growth big time.

Quoted:
That's not really a counterpoint to the fact that magazines won't be nearly as easy as mags for 300blk, and 350L won't work with almost all 30 cal cans.

I agree it should outperform 300blk, especially subsonic.  But people with only a 30cal can won't flock to this, and expensive mags will stunt growth big time.