7.65mm Luger specs
 

What is the optimal barrel length and twist for the 7.65mm Luger? Does anyone know why the barrel length of 11.75 inches was used on the carbines?

Steve,

Are you planning on building a new 7.65 Luger, as several of our board members have done this.

Sieger

Barrel length is a balance between utility, power and accuracy. That is why you see different lengths used.

The longer the barrel length, the higher the potential velocity a given bullet weight and powder load will achieve. It's simply because the high pressure expanding against the back of the bullet spends more time accelerating it.

At the time that Lugers were engineered, instrumentation for measuring the high pressure and velocities, including terminal velocity and energy dissipation, were pretty crude and empirical in nature.

Starting on page 230, the red Sturgess book discusses development of the Luger Carbine, including the history of pistol carbines to that point and issues relating to barrel length. Luger prototype pistols had a range of barrel lengths, presumably for use in testing. A table on page 315-316 shows a large number of experimental lengths.

Ultimately, selection of the barrel length was a compromise between utility / carrying convenience and ballistic performance. Each military commission had it's own priorities. Eventually things settled down to standards.

Steve, Just remember that the German engineers were not measuring in inches. The standard 4" military 9mm barrels were actually 100mms, Navy 150mm, Artillery 200mm and carbine 400mm. So probably none of these even measurements are optimum for either caliber, but up to a certain point, the longer the barrel, the higher the exit muzzle velosipy with a standard power charge. TH

I understand that length in most cases will equal a higher velocity. I was just wondering what the optimal length would be for this caliber. And yes, I know that barrel length was measured in mm's. Sooo, why was the carbine barrel length approximately 300mm long? Was this length chosen just because or was there a specific reason for a barrel around 300mm long?

Lugerdoc, isn't 400mm almost 16"? I was sure that the carbines were closer to 300mm.

I wonder if the 11 inch came from an input from the Kaiser?. In those days, whatever the Kaiser wanted, he got...............probably not the real reason..... :) Just kidding.........

Lots of variables would be considered in your query. Powders all have their own burn rate. Fast powders like Bullseye are used in small capacity, short barreled pieces some. Slower powders like 2400, really take time to get up to steam sorta speak, hence the longer barrel usually. Not to say that 2400 could not be used in a 2 inch revolver, but the daisies in front would have some burn marks; if that matters at all.

We recently in the last decade or so have some new unique powders. Lower pressures, more speed in projectile stuff, mostly proprietary. I think Lil Gun was one of the first that I noticed, and was kinda funky in the beginning of its tenure, but seems to have mellowed out now.

bullet weight...........heavier......is slower usually. Lighter is faster, but has its own issues.

I suspect, an just a wild guess, that the max velocity with a slow powder, light bullet............would be in a rifle length barrel. There is always some powder that burns in the air. With a slow powder, short barrel, a lot of the flash is from powder burning in the air; rather than in the barrel.........remember burn time characteristic.

Now that everyone but me owns a chrony, an interested person could take a barrel to a action, then chop an inch off ever so often after recording info............kinda expensive even with take off barrels, and a heck of a bunch of work. Even then, only the specific details of the ammo, and barrel would be in play............might be different some next time or if you used different components.

So your query is not an easy one............just too many parameters not specified or if they were, still a lot of effort for anything close to meaningful in my eyes.

So few guns today in 30 Luger. Mostly with pistol length barrels, say 4, 6, maybe 8. I own a 14, but never put it on a chrony, most ranges will not allow them here........the chrony on shooting line.

I like the old 30 Luger and its wildcats, just fun stuff.

mm to inches................25.4 is your friend.

Rick W., yes there are lots of variables. I should have specified that factory loaded ammo would be the flavor of the day and I realize that all brands are not the same; some have more oomph than others.

And yes, 25.4 is your friend!

I do believe the answer is :
"no one knows".

Without testing, I would "guess" that a 12" or there about .30 luger barrel gets practically all of the velocity achievable; there is a point at which a longer barrel actually slows the velocity of a projectile- I have no idea what that length is either. JMHO.

I can tell you from first hand experience that a built .30 luger carbine will not function with a 16" barrel(too heavy) but will with the 12" barrel; however, a 16" 9mm barrel on the same lower will function as it should. So with that info and a cup of coffee you can theorize some more. :)

.30 luger factory twist was 1:250mm.

Thanks Don for your input, I was guessing somewhere around 11-12 inches.

..or 1 in 9.84252 inches. Thanks Vlim.

The original Luger carbines also used a different version cartridge with a larger powder charge. They did not use the pistol cartridge.

The Carbine cartridges were designated "DWM 471a for Selfloading Caribine" and had a black body. The headstamp was "K DWM 471 K" After WW-I "K DWM 471A K". They had .4 gram of powder.

Smokeless powder in 1900 was also not the same as today's powder.

Been looking for a box of carbine ammunition for years, that stuff is as rare as hens teeth. And yes, powder today isn't the same as the powder was at the beginning of the last century. Dang, that's a long time ago.

Here few from my own collection :
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