Postino,
I have not seen the Midway numbers on .32 ACP bore diameter, but my opinion is that they are not going quite low enough. And there is considerable variation, as these guns have been made in great quantity by a host of manufacturers, in Europe and in the U.S., for about a century.
A long accepted Lyman specification for the .32 ACP range is .308" - .312". My two Ortgies, an early Colt, and a postwar Mauser HSc measure right at the thirty (.308) caliber groove diameter low end, and bullets sized to that diameter fit the bores and engrave perfectly. .309" would be a common tight fit sizing recommendation for a lead bullet, with .308" used for jacketed bullets.
This is sort of an interesting subject because, for a long time, .32 ACP had fallen by the wayside. Most reloading manuals stopped mentioning it. Now, with the nationwide reform of concealed carry laws and the availability of new high tech expanding bullets, the caliber is becoming popular again; because of the ease of making small and concealable blowback pistols which do not have to deal with high pressures.
I suspect that most manufactures of guns and bullets will lean toward the .308 - .309 bullets, because they can stick with available 30 caliber tooling in the pipeline.
...But then you got me wondering and doubting myself, vis a vis all of the above. So I went down and got a full green (older) box of Remington 71 grain hardball .32 ACP ammo and measured the bullets. Guess what? They are using a diameter of
.305"! Can you imagine one of those bullets rattling down the barrel of a pistol bored to Midway's .313" specification and falling on the floor? That's what happens with such tolerances, even more so in a revolver. Been there, done that. The shot makes a "ploop" sound, no "bang". You can watch it flop into the grass downrange.
Does that further muddy the waters, or what? My conjecture is that this Remington value may be another example of lawyer-engineered ammo that goes "bang", but is guaranteed not to stick in the bore of any gun made since 1905. And yes, I regularly calibrate my micrometers.
Further, all of this relates to Lugers. We have the .30 Luger cartridge, also known in Europe as 7.65MM Parabellum. In my reference book, bullet diameter is .3095", which is close enough to a true .30 caliber dimension of .308". Lyman says .308 - .310 for this cartridge. So the round could just as fairly be called the ".32 Luger", the way the industry plays fast and loose with terminology applied to true dimensions.
I apologize if this is too much detail for some of you, but I'm a ballistics tech junky and spend a lot of time playing with load development, focused on old and high quality guns...like our beloved Lugers; can't get enough of it. As 2nd Amendment advocate Chuck Schumer might put it, "It keeps Phil off the streets."
