From what I understand the 350 legend bullets are largely based on the 9mm dia. (.356"). Winchester is loading ammo using .357" bullets. While I'm aware that either of these bullets are adequate for deer I was contemplating using Speer 35 cal. 170 gr bullets (.358") designed for cartridges like the 35 Rem. and sizing them down to .356". The reason for this idea is that I believe the Speer bullets will be "sturdier" for use when black bear are the target giving me better penetration than the thinner jacketed pistol bullet. Comments welcome please.

having done similar minor resizing for other bullets in other rifles, in the past I don,t see where theres potentially any issue,
yes Id work up handloads starting 3-4 grains lower and step up at only about 1/2 grain steps in the process,
just to be cautious, but I would not expect issues

I don't see any issues either hardcast. My concern is the expansion of the rifle bullet. I guess I'll have to do some type of expansion testing. I don't just want to "poke a .35 caliber hole in a critter"

have you considered use of a 150 grain-180 grain cast gas check bullet?

Not yet but that could be an option. I have to watch which bullet I get because I will be using them in an AR style rifle and I don't want feed issues. But I'm also considering getting a CVA single shot (Elite Stalker) in the 350 Legend too.

The Legend is NOT designed for .355” bullets. It does have a unique SAAMI specification in that it calls for .357”-0.004” bullets, whereas revolver rounds like 357mag use .358”-.004 or .359” for lead bullets, and of course, 9mm pistols use .355”-0.003” bullets.

The problem folks are wrongfully assigning to the BULLETS is actually with the brass. The SAAMI specs for the chamber neck are 0.3789” with 0.3780” cartridge neck, and .357” bullets. That only leaves 10.5 thousands of room for the case neck, so given 2 thousandths neck tension, brass necks cannot be thicker than 11.5 thousandths. Unfortunately, the available brass is largely 12-14 thousandths, so guys run into chambering issues. A more generous maximal spec chamber will allow about 13 thou brass neck thickness.

A friend of mine on Hawaii has a rather generous chamber in his Ruger American, he is able to chamber .358” Speer 180 Hotcors without sizing or neck turning. Personally, I have only built two AR’s in .350 so far, and both readily accepted .357” SIZED 180 Hotcors.

But all of that info is just a demonstration of the process - if you know your chamber neck diameter, you either have to turn necks to fit your desired bullet diameter, or you get stuck under sizing bullets to fit your oversized brass. Personally, I would prefer to neck turn ONCE instead of size every bullet.

For deer with the Legend, I HIGHLY recommend the 180 Speer HotCor, sized to .357” if necessary.

That's the bullet I was thinking about Nomercy. But I plan on sizing to .356".

If it meets your neck tension, brass neck thickness, and chamber tolerance, then you’ll be well served.

Thats odd because Hornady's bullets for reloading 350 Legend are indeed .355.
https://www.hornady.com/bullets/rifl...5-170-gr-sp#!/
https://www.hornady.com/bullets/rifl...-165-gr-ftx#!/

https://cdn0.thetruthaboutguns.com/w...GEND-SAAMI.pdf

I can appreciate that self-guided study is a burden...

SAAMI Specification page for .350 Legend