In V-V's case, it was their 4" test barrel. With my handloads, the pistol with the shortest barrel was a Ruger SR9. After I bought the TP9sa with it's 4.47" barrel and hearing from the US Distributor, CAI that it was rated for +P loads, I fired those same rounds from the Canik and they chrono'd around 1175 FPS with the Hornady 147 gr. XTP, the only 147 I've tested personally that would stand up to that much velocity. And, consequently, the bullet V-V used in their data, with velocity rated from their pressure barrel, and the last time that V-V published pressure rated data, with this particular recipe being in it, 33,000 PSI/CIP was the pressure max they limited themselves to.
Before anyone gets nervous about that, simply go to the Lapua site for V-V load data. But before you go, and after posting this about a gazillion times, the SAAMI MAP for the 9 X 19mm is 35,000 PSI/33,000 CUP and 33,000 PSI/CIP is lower then either.