Building a .338 lapua on a 700 action is a mistake.
Just because Remington decided to cash-in on the market desire for the big medium bore ctg don't make it a good choice.
Like that long bodied Lapua ctg? Have you seen the .338 Norma? Then there is the .338 edge which needs no boltface alteration, no other gunsmith work if you begin with a factory Ultra Mag action.
Really a big deal to open that 700 bolt rim further, from .535" to .592" Really leaves almost nothing of the "ring of steel" surrounding the ctg head.
I owned senderos in .338rum and .300rum. Sold them. Got into the .338/300win as a better solution allowing more versatility with handloads. Basically it duplicates the .340wby and .338 Dakota, but can be downloaded to .338win levels. The case is large enough to go high velocity and not so large you can't load it light w/o risk of detonation.
Really a mistake to push the 700 receiver. The Weatherby action, The Sako M995, some of the non-700 clone custom actions are more suited.
Want to save yourself money and time? Buy a Sako TRG-42 and call it a day.
On the cheap? The .340wby chambered Fibermark.
Study the loading manuals and see for yourself that the .340wby is not lacking when compared to the .338 Lapua. Norma brass at $2ea. Once-fired is plentiful, or neck-up the even more common .300wby. Cheap brass from R-P and Federal also out there, plus lots of loaded ammo.
Got the itch to build? Doing a Rem 700 mod'ed action is the best way to be sure you will NEVER recover any of the couple thousand you will put into the project. The time you will never recover.