Re: AH: need to know about first generation 1911 ACPs
Better yet, since he has to "shoot his way out" and the 45 has such a small magazine, use a good old Browning High Power. Also invented by J.M. Browning (an American) it was made in Europe and would be common for a German officer. You could have him opt for the Browning in place of his Luger because it's more reliable and carries more rounds. You could even have him "hollowpoint" his own ammo using standard German 9MM.
Even if the 45 was a prized trophy of German officers, that's not well known and most readers will see it as a mistake. Altered ammo is a serious No No in the military but that's not a consideration for your renegade officer.