In my experience developing loads for many 338 Lapuas as well as the 338 AX which is an improved version of the Lapua and from what I have seen, your well above what is normal for this bullet in a standard Lapua. Could be a fast barrel but even then your a bit high. FOr a standard Lapua, I would say 3100 fps is about tops of what I have seen with this bullet.
The main problem with custom rifles
that are built correctly will not show normal pressure signs, especially when combined with a strong case such as the Lapua which will easily handle around 70,000 psi before the primer pockets loosen up.
An example of this that I always tell my customers is about a customer of mine that I built a 257 STW for on a fully trued Rem 700, 30" lilja 1-10 Lilja barrel. The load data I sent home with the rifle was with a 100 gr BT at 3850 fps which I have found to be about the top for STW in Lilja barrels.
Well, he had gotten on line and found some reports that the 257 STW is a 4100 fps chambering with 100 gr bullets in a 28" barrel that were posted by a rifle builder that I personally believe is very irresponsible. Anyway, my customer started building up the powder charge and sure enough he got to 4100 fps and was very happy, that was until he resized the cases he had used to develope the loads. The primers simply fell out of the cases when he tried to prime the cases. He came to me pretty upset as he had shot over 50 rounds of brass before he found the problem.
He commented that something was wrong with the rifle as the bolt could be opened with one finger on a fired case and extraction was effortless as well. I explained to him that this is common with a trued receiver as they do not show the normal tight bolt signs from high pressure like you would in a factory rifle.
After a bit more education, he decided to go back to the 3850 fps load and not look for greener grass elsewhere.
My point, do not think that if your getting velocity levels that are far over what is normal for a given chambering that you are getting these velocities with normal pressures. Velocity is simply a function of pressure behind the bullet and the time this pressure acts on the bullet while its in the bore. There are other factors but simply put, if your getting very high velocity, its mainly a result of higher pressures.
I once had a Ruger M77 MkII chambered in 7mm Rem Mag. I developed a load with the 140 gr Ballistic Tip using Reloader 22. I was looking for pressure signs and had none in any way so I kept increasing the load looking for signs that I should stop. I got to 3450 fps and still had no pressure signs at all, even primer pockets were snug still. How could this be. I was pushing a 140 gr bullet as fast or faster then even a 7mm RUM factory load.
After thinking about this for several days I decided it was wise to drop back to 3300 fps and be happy. Your chrono is your best friend in predicting pressures, even more so then trying to read pressure signs from your rifle or brass, pay attention to what your chrono is saying. An extra 100-150 fps is not worth the strain you are putting on the entire rifle system for that extra velocity.
Just my opinion from what I have seen with similiar handloading results.