Study Identifying Luger Caliber: .30 Luger or 9mm Luger?
 

Here are some illustrations to help with identifying the caliber your luger was made in.

The original Luger cartridge was the .30 Luger (7.65x21mm Parabellum), a bottleneck cartridge. The chamber that this cartridge fits into has a stepped shape that supports the bottleneck.

The 9mm Luger (9mm x 19mm Parabellum) cartridge has a similar cartridge base, and does not have the bottleneck. This is why the one Luger magazine design can work with both cartridges.

Several posts mention the "pencil test". The fact is that a hex shaped (sharp edges) No. 2 pencil Will snugly fit down a .30 Luger caliber barrel. A round No. 2 pencil generally will not fit down the .30 Luger barrel.

Both pencils will loosely fit down a 9mm Luger barrel.

The pictures attached to this post are annotated.

They first show a 9mm cartridge placed in a .30 Luger barrel's chamber. It will NOT fit properly into this chamber, and would do damage if it went off (photos are of a dummy cartridge). It will stick out of the chamber, and the toggle train will not go into battery.

Next, pictures show how a 9mm Luger round will rest on the end of a .30 Luger barrel, and a 9mm Luger barrel.

Next, a Hex No. 2 pencil fits tightly into a .30 Luger barrel, and a Round No. 2 pencil rests on top of the .30 Luger Barrel.

Next, a Hex No. 2 pencil fits loosely into a 9mm Luger barrel, and a Round No. 2 pencil fits loosely into a 9mm Barrel.

Hope that these help you identify the caliber of your Luger!

Marc

Hard to believe, but this "primer" seems to have been necessary lately...
Thanks, Marc!!

Here's my contribution - 7.65mm Luger on left; 9mm Luger on right...

And since most of us will have a 5/16" drill bit lying around, the bit will fit in a 9mm barrel but not a 7.65mm barrel... :thumbup:

(It'll be a very sloppy fit in the 9mm) :D

Rich..And since most of us will have a 5/16" drill bit lying around, the bit will fit in a 9mm barrel but not a 7.65mm barrel...

That's not true! I turned on my drill and it went right in! Few shavings and chips but in it went!

HAHA! Seriously... should move this over to a sticky. Good Job Rich and Eric

Excellent illustrations in an easy format.

A very nice tutorial, that proved needed lately.

We need to keep Jerry away from power tools! :) Best stick with a needle and thread, Jerry!

This question keeps coming up. Sticky?

Marc

Excellent Tutorial on distinguishing .30 caliber from 9mm. I will make it a "sticky"!

Up until 1908 with the exception of the commercial fat barrel 1902, 7.65 including the Swiss was the only calibre that I am aware! All the 1908 models Army, Commercial and Military were the 9mm. A few 1920 carbines retained the smaller calibre 7.65. as many used leftover parts during the Weimer era~

Was there a specific time when the switch occurred from 7.65 x 21mm (.30 Luger) bottleneck cartridge to the 9 x 19mm Parabellum cartridge? Yes, almost immediately after George Luger invented it.

Was this transition across the board (did all manufacturers change simultaneously)? Yes, since there was only one manufacturer, DWM.

What was the reason for the change (i suspect it had to do with the forever argued concept of knockdown power)? Exactly! Good guess! There is little to argue about here really. BIGGER is better 100% of the time.

The 7.65(.30 Luger) was in production till 1947, so there were no switch as such, but parallel production.