Before any of you start in on "why" I built a 350 Legend, let me tell you that I did it because I wanted to do it. I need a 350 Legend in my inventory of AR platform rifles about like I need a third nostril. It ain't a "need thing," fellow THFer's. So, here's the list of stuff I assembled to stitch it all together:

Upper: Aero Precision Flat Dark Earth upper
Barrel: Shaw stainless steel, 18" long, in 350 Legend caliber (purchased from E. Arthur Brown company)
Compensator: Lone Wolf Distributors .40 caliber stainless
Gas block/tube: AR Stoner adjustable, low-profile, carbine-length
Handguard: AR Stoner V2 ultra-light, M-Lok, 15", Flat Dark Earth
Dust cover: Strike Industries, polymer, Flat Dark Earth, removable (without having to remove the handguard or barrel)
Charging Handle: Strike Industries, Flat Dark Earth

Lower: Aero Precision multi-caliber for AR-15
Trigger: Palmetto State Armory two-stage trigger (3.5 to 4.5 lb trigger pull)
Other lower parts (pivot and take-down pins, springs, safety selector, etc): AR Stoner lower parts kit
Pistol grip: Magpul MOE, Flat Dark Earth
Trigger Guard: Strike Industries Billet Fang Aluminum trigger guard, Flat Dark Earth
Buffer tube: Strike Industries 7-position carbine-length, Flat Dark Earth
Buffer: H2 weight
Buffer Spring: carbine length
Butt stock: Magpul MOE carbine stock
Buffer tube castle nut: Strike Industries Tribus Enhanced Receiver End Plate, Flat Dark Earth

Most items were purchased from Midway USA, but some were purchased from Lone Wolf Distributors, Arm or Ally, and Palmetto State Armory since neither Midway USA nor Brownells had all the parts I wanted in the color I wanted.

I've had dies and bullets on order for a few weeks now, so I'll let you know how this thing shoots once I get some loads made up and tested.

Most of us are way past the needs phase on firearms. Congrats on the build, looks great!

You done good. Pretty good list of stuff.

One vendor I’d recommend that’s not on your list is Primary Arms, down in Houston and great to do business with. A buddy of mine turned me into them and I‘ve hated him ever since

I like their branded scopes.

Sounds like a fun project... I built my 16" 10mm against some advice... but I really enjoy it.

Well I don't need one but may get an upper from somebody, an old buddy that now lives in Michigan wants me to hunt up there and the 350 Legend is legal in the shotgun zone. So do some load testing for us!

I plan to do that, rickt300! I have so darned many projects going on that I'm having to keep lists just to keep up with them!

When I did my 350 AR and bolt rifle builds about 5 years ago I first designed the cartridge , then I cut a reamer . Bought some .355 barrel blanks and turned them down to fit either an AR or bolt rifle . Had to figure out what size gas system was needed and make that . Next was modifying the feed ramp and a magazine to work with the cartridge . Next was making 100 cases for load testing . Tested 10 different bullets from 140 to 200 grain with 12 different powders . The gas guns did like a little different load than the bolt rifles . The 180 bullet was the best overall performer . With 2 bolt rifles and 3 AR-15's built for 4 people we tested them in the field on deer and pigs . After about 50 total taken we were very happy with the results .

Nice build.....I like that rail....

Here's a couple of promising loads to consider; they are working well in the new Legend. By "well," I mean about an inch and a quarter, 5 shot groups at 100 yards off a rest: These are the first rounds fired through the new barrel, and my experience has been that most new barrels settle in between 100 and 150 rounds. I'm thinking groups will tighten up a bit with more range time. And I haven't started playing with COL or different primers or different powders and bullet types and weights. It's a long road to one hole accuracy! Everyone's mileage will vary, of course.
Hornady SST, 180 grains, 34.2 grains of Accurate 1680, MV 2479
Hornady FTX, 165 grains, 24.6 grains of Hodgdon Lil Gun; MV 2101

Mikei, I too am working up loads for my AR-15 350 Legend and I'm struggling finding an accurate load. I'm going to try your 165 FTX load, I've tried 27.0 grains of Lil' Gun with that bullet and accuracy was not good, I think I may be pushing it too hard as my velocity is 2300 fps out of my 16" barrel which seems a bit high.

I'm interested in your AA 1680 data, is there any published data for this power in the 350 Legend?

Also, I can't find a .355-.357 180 grain SST bullet on Hornady's website, are you referencing to the .357 180 XTP?

Liking this build, I bought a Ruger American in 350 Legend. Shot several differs factory rounds down range. Have not reloaded any yet, but am building up inventory of brass. Saw video of new 9mm ammo online today with a 185 gr bullet. This may need to be looked at for hogs. Keep me posted if you find the magic load.