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.

You're the first, maybe the only person, I've seen load 38/357 that heavy. Based on results you've posted in other threads, it has potential as a subsonic hunting round. I really wish I had built a 77/357, instead of the 77/44.

I'm trying not to increase my cartridge diversity. This one sounds cool enough to get... maybe.

A 265 grn subsonic out of a short bbl suppressed sounds like a great indoor burglar round.

This cartridge will really shine suppressed once some faster twist barrels and 300+ grain expanding projectiles are made.

The less time I spend trimming brass the more time I spend making spent brass.

It's also annoying as hell.

It uses .357 bullets not 358. As in pistol bullets. What’s I look forward to is the development of higher BC .357 bullets

I bet it shoots .358 bullets just fine.

Do want, at the right price.

The Winchester factory loads announced at launch don't look like pistol bullets. They are more akin to the bullets available for 35 Remington or 358 Winchester.

And the 357AR guys (the predecessor, at least in spirit, to the Legend) were using a variety of pistol and rifle bullets and adjusting COAL to match.

The Swift 180gr A-frame designed for 357 Magnum could work well too, especially from short barrels. That would be an interesting 150-yard hunting round from an extremely short barrel.

Played with QuickLoad some more this AM - looks like muzzle pressures from the short barrels are going to be significantly higher (50% or more) than a 147gr +P 9mm from a 4" barrel. Muzzle pressures start to match up around a 16" barrel, so you may see can manufacturers certify their 9mm cans with fixed adapters for use on 350 Legend, but with fairly long minimum barrel lengths. And the pressure doesn't begin to cover blast baffle erosion with the higher velocities from the Legend.

This is making me want a 357max barrel for my Contender.

Get a Giraud.  Spendy, but I fucking love trimming now.  My wife got me one for Christmas.

I wish I would have bit the bullet so to speak and gotten one years ago.  I really do.

Do yourself a favor and avoid PTG like the plague.

The last reamer I ordered from them it took them 3 attempts to get the dimensions right.

Their out of spec reamer ruined a $450 AR barrel in the process which I sent into them and they told me to go get stuffed.

On my last build my smith ordered a reamer from them, it went dull halfway through the cut.  Any decent reamer should last about 10 full rifle chamber cuts.

Go to manson.

This isn't the only PTG product I have had issues with.  They used to be THE company to get great products and service from.

Well, I think I'm going to need a new receiver in the future.  I'd like to see what it does, but I kind of want.  This is why I like ARs.

I know there are a lot of .357" diameter bullets, but how many are designed to go 2000fps+ for use on deer?

I've been following this thread from the beginning. This is the first option to .556 that I want.

Not many.

Which is why we'll be loading with .358 rifle bullets

It won't take long for bullet makers to come up .357 options.

In my 357AR, I currently run the Hornady 200gn FTX and the 200gn Round Nose. For plinking ammo I am using the 158gn XTP HP's. The FTX load is running 1900 fps and the XTP load is at 2191 fps.

I know the 200's are slightly below the 2000fps mark, but the two deer I shot with it this season didn't complain. I was not able to recover the bullets since they passed through. But the exit wound was over 3/4" on both of them. One was at 20 yards, the other was at 80 yards.

I am excited to see more bullet options available though, plenty of practice and development time coming up!

this will kill 300 blackout.

Im with ya on this one

One can only hope

Several people have been using .358 rifle bullets in the .357AR and loading accordingly. Back the load off and work up to what's good. Same idea will work well here.

The 357AR barrels were made with .358 blanks.

I doubt it.

Squeezebore is a thing and it will work just fine. One thousandth isn't even that much.

The impact on accuracy and velocity while staying within safe peak pressure is another question entirely. Performance may be less than ideal, depending.

I do too.

It's still a neat cartridge that fits extremely well in the straight wall hunting niche.

And the world always needs more .35s.

When uppers come on the market,i will have to give this a try.

Other than AR compatibility, the mundane 44 mag offers the same or better performance on medium / big game.
200gr at 2100 fps @ 42000 psi
Larger selection of  (300-340gr WFN) heavyweight bullets for sub/ hunting applications.

As far as it replacing the 300 BO.....

No way. Way more people have 30 cal cans.

Username checks out.

I've mostly lost interest in new AR related stuff, but I do believe I'll be needing one of these.

He's almost as bad as the 6.5 Grendeleerzs...

You two dum dums act like Winchester reinvented the wheel....lol

Just pointing out the obvious. Can't fix stupid I guess.

My favorite part is the “other than AR compatibility” like it’s a small thing.

Will be trying one of these.

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

Many 9mm's actually have .358" barrels.  When the big light hits the bullet in the ass it will bump up or obturate. The 30kpsi is enough.  A thousandth or two doesn't matter so much in a short range rifle like this.  I wouldn't be happy with a it in a bench rest rifle or long range target rifle, but here it will be fine.

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.

Always been a 35 Remington fan love my model 8 similar ballistics in a modern platform count me in for one.

I think it was a thread I read on here about a lot of Sig guys shooting .357 bullets after slugging their barrels.

That's what I was thinking in subs wouldn't this be good with a 9mm can?

But I don't know much about cans. Ballistically this should make sense in a subsonic application unlike BLK which seems lame in subs.

Some will and some won’t. Pressure is the enemy and running a big heavy bullet can raise pressures substantially. A 180 or 200 grain bullet pushed to 1050 would likely be too much for some cans if they were built with 9mm in mind.

I shoot .357 bullets in my M&P 9mm

Intersting. Any pressure signs? Or do you reduce the loads a bit?

A 0.001 inch difference in size will have almost no discernible effect on pressure. A change between two bullets of equal weight but different bearing surface will impact pressure more than a small diameter difference.

Who is going to make uppers first and when will they be available ?

But i want to shoot it supersonic too,  with a can...

9mm is .355 but I hear your point.

I bet this round will help Liberty Cans sell more mystics

Apparently CMMG and April I think