Specifically, what allows a cartridge such as the .338 Lapua handle such high pressure? Is it just the thickness of the case web/primer pocket area or the quality/hardness of the brass or both?
Here is a list of SAAMI pressures for different cartridges
Max Chamber Pressure - SAAMI Specs
Notice the 338 Lapua listed no standard pressure, but I would be surprised if anyone was running a load much over the 65,000 psi standard for modern high pressure calibers like the RUM's and WSM's. IOW the 338 Lapua case should not have to withstand anymore pressure than a 338 RUM, or a 300 WSM or even a 270 Winchester
Pressures are regulated by the amount of powder, burn rate of powder, chamber dimensions, bullet weight and bore size so that it would not matter if you were loading 91 gr of RL22 in a 338 RUM or 69 gr in a 300 WSM you would get the same approximate pressures.
Therefore the pressure on the brass is the same in both
Now if someone can show me where the accepted pressure for the 338 Lapua is more, say 75,000 psi, then I would say that Lapua has a metalurgical secret that they use in the their "super brass"
In Quickload, the 338LM is SAAMI max at 60Kpsi, which implies that it's not a 'high pressure' design compared to many other cartridges.
Handle as in lasting brass life?
Primer pockets staying tight?
This I think.
I responded previously on this thread with the standard answer of basic design, quality control etc. While this is certainly important and everyone is pretty much saying the same thing, I have thought more about it. Given those basics, after many years of working with lots of different rounds, the strongest, longest lasting cartridges have been the ones that give me the required accuracy, velocity, and distance, when my load is built to work well within the maximum SAMMI pressure of the cartridge, and, importantly, the rifle chamber has the correct dimensions. I have had 308's and 223's that a 100 box of Lapua brass gets me over 1500 rounds down the barrel with maybe a few annealings required. One the other hand, I have just stretched slightly the limits of the same cartridges and they fall apart in a few reloads with case head separation, loose primer pockets, etc. and the initial pressure signs were not always obvious. I have a buddy that uses one box Lapua of brass per barrel with his 6BR. Overall, I think that given the basic design and manufacturing process is sound, the specific load and rifle combination is what creates a strong cartridge.IMHO.