I got an AR in 335AR Max just before the 350L was introduced. Same ballistics. For a while, I followed a Facebook group specific to the 350L. Tons of real experience has been shared and is available if you are willing to go look at it.
From a ballistic standpoint, there is not much to gain by going with a barrel longer than 16".
If you reload:
- Case length is more important than for a typical round.
- Some recommend not using Starline brass in an AR.
- Start shopping for the new 350L specific bullets (0.355") now. Using them (instead of 0.358" bullets) makes thing easier, but availability is not good.
- If you do want to use 0.358" bullets, get a Lee 0.356" push through sizer die and use it. This has been proven to work fine.