The European Designation for .45 GAP is 11.43x19mm
Nobody should care about the European designations for American cartridges, let alone a cartridge that was as big a failure as .45 GAP.
But the Taxonomist in me likes to know both names so when I come across odd cartridges with only Euro names, I can compare them all on equal footing!
On that same logic:
If we anglicize 7.63 Mauser to .30 Mauser, and 7.65 Parabellum to .30 Luger, why don’t we give 9x19mm Parabellum the english designation .38 Luger?
When Mauser rereleased the Parabellum pistol in the late 60s/early 70s, one of the test guns was marked 7.65 Parabellum/.30 Luger and the other 9mm Parabellum/.38 Luger…although it does not appear that that caliber designation ever made it to the production models.