I could be wrong:
The bottom of the breech block is cylindrical. The bevel sits against the nose of a round in the magazine. This bevel keeps the round in the magazine in line. If it were not beveled and still cylindrical I could imagine a round would be forced to the left or right possibly binding the action.

 

Just picked up my 1912 Erfurt, the breech block lacks this bevel. It was retrofitted with a holdopen after not getting one from the factory.

 

Interesting and unusual not to have the bevel. It could raise some issues if you shoot the gun. Do you intend to test shoot it?

 

I do plan to, this one also shows a decent bit of evidence that it has been used in its lifetime. Obviously I cannot tell if from the wars or in the 80-100 years after.

 

The gun is completely matching and yes, conditions of all parts are congruent with one another and properly Erfurt proofed (including the ejector, both grip screws, and even the S-link). I had to go back to work and leave the gun at home so I can always look in a few hours when I get home for anything else.

 

Here are four Erfurt breechblocks. Three 1917’s and one unknown.

 

Here are four Erfurt breechblocks. Three 1917’s and one unknown.

Hey Sega,

what year is this Efurt and Serial Number?

 

Thanks for sharing the pictures!

 

The way it looks on a postwar assembled (PX) Krieghoff (which is similar to the machining/beveling on my 1940 HK).

Still looking for your answers to the OP question.
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Is it possible the lack of it on the early pistols is related to the fact they used bullets that were truncated cones rather than round nose?

 

Do we have pictures of breech blocks of “early” Lugers that don’t have that bevel? I know that my two P04 Navies have it. How early are we talking about.
I should add that the “bevel” is not likely used to help with guiding the bullet.

 

All of these early Lugers have the tiny bevel. (Pictures from Borchardt & Luger)

Swiss 1899 trials pistol.

 

And I add that the bevel is shown in the blue prints for the P04 (signed by Luger himself). It is even assigned a length dimension.

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I’ve been experimenting!

(1) A fresh 9mm round was placed under a snap cap (for safety).

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(2) As the Luger’s toggle was held back by the hold-open latch, the magazine was inserted into the grip.
(3)The toggle was pulled back by hand to its extreme rearward position and then released suddenly.
(4) The magazine was removed, and the round inside was inspected. The pictures below show the markings left by the bolt (point of initial impact).

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The rear edge of the tiny bevel (notch immediately behind the hold-open cut) left a mark on the case neck just before the bullet. It appears that the back of the notch strikes very close to the top edge of the brass first, before the bolt belly touches the body of the round and drags across the round while it’s still in the magazine.

Here’s how another fresh 9mm round—sitting directly below the top magazine round being chambered—looked after four repetitions of the above experiment. Sort of exaggerating the point of initial impact markings. Note that the round has rotated slightly during this second experiment.

On the Luger I used, the notch behind the hold-open lip is generous, measuring 2mm in length. Without it, the sharp edge of the hold-open cut on the bolt would strike the bullet directly, latch onto it, and then attempt to push it forward—potentially causing a jam on the feed ramp while another round is being chambered.

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I’ve been discussing* the purpose of this tiny notch with @G.T. , and here’s what he had to say (posted with permission): "I'm almost certain it involves the sharp edge requiring some relief so it doesn't stall and catch on the bullet! I've actually had this happen and I had to put the relief on the breech block to cure the jam. Also, the relief cuts vary greatly, not a lot of time spent on accuracy, any bevel was enough … just so you are aware of it, the round next under the breech block moves back and forth rather dramatically just like a little hammer! When it drags forward it causes a jam on the feed ramp, best GT“

* [Edit] Also had ongoing discussion on it with @SegaDreamcast, and a brief exchange with @Doubs.

 

Explains why when I was looking over every other one I had (all DWM’s) they had this bevel there, and yes it varied widely in shape. I didn’t grab pictures though, will have to do so later.

 

It is amazing how accurate this Animation is (a short clip from a Youtube video). You can slow it down and check the point of impact.