I've been playing with an AR15 upper in 350 Legend lately and I must admit it is kinda fun. Looking forward to taking it to Oklahoma and whacking 3 or 4 deer with it (if our hunt happens this year) and maybe a hapless hog or 2.
I've found that H110 or WW296 (same powder) is truly THE powder for this cartridge, 23 grains and a 170 grain Barnes TSX are working great together, light roll crimp.
With a 16" barrel and a 3-9 compact scope I am printing 1" five shot groups at 100 yards 2140 fps.
It is ringing my gongs with some authority so I can't wait to see an impact on game. In water jugs and sand bank tests I've tried 170 grain Hornady SP's, 165 Hornady FTX, 180 Power Points and the 170 grain Barnes TSX, I listed them in softest to toughest order.
I found that the Winchester 180 grain Power Points are great factory rounds and shoot same POI as the 170 Barnes and produce same group size.
The 350 has gained popularity with some middle states who need to comply with the "straight wall cartridge" rules.
I just found it a fun alternative in an AR15.
So far I have assembled and killed deer with AR15's in .223, 6x45, 25x45, 7.62x39 and now the 350 Legend.
I helped a buddy assemble a .277 Wolverine and a .358 Yeti both on AR15's with a lot of extra horsepower over the .223.
Fun stuff for those that are into something a little different.