I haven't done any vana runs with the magnus guns in I would say about at least a year and a half so my memory might not be the best but if I remember correctly, the orbs will stop the shot if you hit them (again I am not sure). But if I am actually wrong and the charge does go through to hit vana, the hit won't do much at all because it won't be able to hit him multiple times. The most it will hit him is twice and any other gun that is 5* and vana isn't strong against will then be doing more dps than a magnus line gun.

I am actually going to test this right now, so I will give you a concrete answer once I complete my test.

EDIT: Just got done testing it and I still can't really tell tbh. Some of my shots looked like they went through the orbs and they hit him while others blew up when they hit the orbs and yet there was nothing else near his orbs. So I don't know if it is just a ping related thing (I am on a 2 bar most of the time) and they still stop the shots or if there was some sort of invisible wall/bug that stopped my shots from doing dmg.

So my thought is that while I can't tell because of my ping if they stop the shots, It is still without a doubt better to use any other gun that isn't weak against vana. I was only able to get 1 hit per charge on him if they landed, so with my loadout that was like 440 dmg. Which compared to the blitz or even regular shots from a blaster, it isn't at all worth using a magnus line over any other gun.