338 Lapua and 338 Lapu Ackley Improved. . .
For what its worth:
I have built a few 300 RUMs, 300-338 Lapua Magnums, 338 Lapua Magnums, and 338 Lapua Magnum AI's. I've done this on a variety of actions to include Remington Long actions. I've not experienced any trouble what so ever. I've pushed some of these to ridiculous velocity also.
The way I look at it is this:
If you are relying on the thin margin of material on the bolt to some how prevent the case from rupturing (or containing a rupture), you are only fooling yourself. By this line of thinking, a lot of other actions would be disqualified. We can sit and rattle off names all day of companies chambering guns in this caliber with no ill effects.
If the gun is headspaced properly and if bolt to breech face clearance is kept conservative, experience has shown me that the good ol generic 700 Rem will run all day. A Sako extractor will fit and it will work.
I think the problems and horror stories associated with this is when folks start wild catting the big cartridges to make magnum calibers.
The 416 is not a high pressure case. The 338 Lapua Magnum's bloodline traces back to the 408 Jeffreys. The relation ends there though. The brass is thicker and harder on the Lapua cartridge. This allows for the elevated pressures. 60,000 CUP if I'm not mistaken. A 416 will do that for awhile. . .
I realize lots of people fiddle and fuss with hot rodding 416 cases. All I am saying is that you are running on borrowed time. The case was never intended to operate at that performance level and if/when it does let go on you, all bets are off and I hope you have an ER close by cause you'll probably need it.