From my perspective Ronnie Barrett's 416 is a way to satisfy the CA market for a big boomer with performance similar to the 50BMG. I have not fired a 416 Barrett, but the trajectory is reportedly flatter then 50BMG for any realistic range. As has been mentioned, with this much powder capacity 416 Barrett barrel life will be 500 or perhaps 1,000 rounds if you load lightly. But don't let this stop you from buying a 416 Barrett if you want one. How many guys shoot their rifles enough to burn out the barrel anyway? If you PLAN to shoot 500 rounds a year then this may not be the way to go, but if you are like most of us and shoot a couple hundred rounds the first year and then 50 rounds a year afterward then it makes little difference anyway.
Another issue is if you want to shoot FCSA competitions you will need a rifle in 50BMG rifle.
There is a slightly shortened 50 caliber round called 50DTC (I think this is the name) which is supposed to have the same performance as 50BMG and it is still 50 caliber so you can use all the same bullets. This caliber is likely to be allowed in all FCSA competition by mid-year so as to appease the CA shooters.
Which brings us back to 416 caliber. Not many bullets are available and those that are are pricey! If you don't handload you are at the mercy of Barrett for ammo. 416 Chey-Tac has been around for years and still I have never seen loaded ammo for sale at the stores I visit.
EDPMEDIC has a good point in suggesting the 338 Lapua. You can buy loaded ammo in 338LM and components are available if you handload for a fraction of same quality 50 caliber components. In an accuracy built custom rifle 338LM is superbly accurate out to 1,500 yards or so. When I wanted something bigger than 30 caliber it came down to 50BMG or 338 Lapua Mag. I couldn't resist the 50BMG lure and have one being built right now. But a 338LM has some real advantages as well:
It can be built on a Remington 700 Magnum action and thus any of the good aftermarket stocks can be used (McMillan, etc.)
Just some thoughts,......