Your current boltface is too small for a Lapua. Read this below and it will give you the info you are looking for. This was taken from another post here on LRH by J E Custom
Some times when considering a rebarrel and chamber or cartrige change you need to
know what round will work without boltface and extractor work.
I have a cheat sheet/ready reference and thought I would share it with every anyone
that is interested.
All of these groups of cartriges should interchange without bolt face and extractor
work.( some work on recever rails may be needed to improve feeding ).
As far as wild cats what ever the parent case was it should work in the action listed.
I know this list is not complete but it's close.
Short actions with a bolt face .Dia of .384 +/-
17 Rem, 204 Ruger. 222 Rimingtion, and 223 Rem.
Short actions with a bolt face .Dia of .470 +/-
225 Winchester, 22/250 Remingtion, 6mm Norma BR, 243 Win, 250 Savage, 260 Rem,
6.5/284 Norma, 7/08 Rem, 284 win, 300 Savage, 308 Win, 338 Federal, 35 Rem, and
the 358 Winchester.
Short actions with a bolt face .Dia of .540+/-
223 WSSM, 243 WSSM, 25 WSSM, 7mm Rem saum, 7mm WSM
, 300 Rem saum, 300
WSM, 325 WSM, and the 350 Rem Mag.
Long actions with a bolt face .DIA of .470 +/-
220 Swift, 6mm Rem, 240 Weatherby Mag, 257 Roberts, 25-06 Rem,
6.5x55 Swedish, 270 Win, 7x57 Mauser, 7x64 Brenneke, 280 Rem, 30/06 Springfield,
8mm Mauser, 338/06 A Square, and the 35 Whelen.
Long actions with a bolt face .Dia of .540 +/-
257 Weatherby, 264 Win Mag, 270 weatherby Mag, 7mm Rem Mag, 7mm Weatherby Mag, 7 STW,
7mm Rem Ultra Mag, 300 H & H, 300 Win Mag, 300 Weatherby Mag, 300 RUM, 303 Brit,
8mm Rem Mag, 338 Win Mag, 340 Weatherby Mag, 338 RUM, 375 H & H, 375 Weatherby,
375 RUM, 416 Rem Mag, 458 Win Mag, and the 458 Lott.
Long actions with a bolt face .Dia of .585 +/-
30/378 Weatherby, 338 Lapua, 338/378 Weatherby, 378 Weatherby mag, 416 Rigby,
416 Weatherby Mag, 460 Weatherby Mag, and the 470 Nitro Express.
I hope this information helps in deciding what your next build will be and minimize some
of the cost.
J E CUSTOM
Hope this helps