Only with the intent of hunting or going to a range.
It is not legal to openly carry a rifle in order to intimidate.
Those are "fighting words", and deserve a deadly response.
I have been to dozens of demonstrations, and never saw a rifle carried like this, (except Korean grocers on their own roof tops, in LA).
It was clearly illegal for Rittenhouse to deliberately try to provoke and intimidate with the open carry like this.
And again, Rosenbaum had more right to use deadly force than Rittenhouse, because Rittenhouse was the original violator.
We have no idea what Rosenbaum would have done with it.
Assuming a deadly intent by Rosenbaum is not legal.
We can assume Rittenhouse was the one with the deadly intent, since he brought it.