Lorenz bore size question.

[apriestley]

I recently purchased a Lorenz extra corps carbine and am trying to get a load worked up for it. When I first took it out to shoot I found that the bore diameter seems to get much larger toward the breech starting at about the rear sight. It’s very tight at first but opens up around the rear sight. When shooting patched round ball the patches were actually slipping past the ball and thus not hitting anything.

I tried out two types of conicals, one being a .543 minie and the other a .548 Wilkinson from the new Moose mold. The .543s, were pretty easy to get down the first half of the bore but just fell straight down the second half, I also had a very hard time even getting them on the paper target at 50 yards. The Wilkinson’s were very accurate and I was able to put three bullets in one hole. The problem was that these were so tight I had to use a ball starter and a few light taps with a mallet to get them loaded. By the time I got them down to the rear sight, they too were very loose but at least i could hit with them.

Is this gradual tightening of the bore normal for Lorenz rifles? For further load development I am thinking of sizing down to .546 or .545 with the Wilkinson’s.


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[Mike McDaniel]

IIRC, the Lorentz bore is .547.

[geezmo]

Check out Capnball's presentation on youtube below. About a third of the way in he explains what you're talking about. It increase in diameter at the breech is supposed to be a place for fouling to accumulate.


https://www.youtube.com/watch?v=mPVrXiUwzC4 (https://www.youtube.com/watch?v=mPVrXiUwzC4)

[gmkmd]

Original Lorenz rifles did indeed have a choked or tapered bore, as did certain other guns as well. Obviously you have to use a bullet small enough to easily load past the smallest bore diameter (at the muzzle), and pure soft lead to maximize bullet expansion. The bullet should expand upon ignition to fill the larger diameter at the breach, and as it travels toward the muzzle it becomes choked to further improve engagement with the rifling.

[Gary Van Kauwenbergh, 101]

For original specs, see page 5 of http://acwsa.org/Documents/LorenzManualTranslation.pdf (http://acwsa.org/Documents/LorenzManualTranslation.pdf) The originals did not have a gain twist nor tapered bore; they just honed the bore out a little more from about the area of the rear sight down to the breech (.0072 inch or 1 'Puncte'. Page 29 describes the cartridge, that was loaded with the bullet. The lube was on the paper.

[Don Dixon]

Ritter von Lorenz?s barrel design was unusual. In the original .547 inch [13.9 mm] caliber weapons, the lands and grooves of the barrel were opened up by approximately one Punkt [0.00717 inches/0.182 mm] from the breech to five or six inches [127 to 152 mm] down the bore toward the muzzle. This left the grooves approximately 0.025 inches [0.635] mm deep at the breech and 0.02 inches [0.508 mm] at the muzzle. This space was called the Rundung [drop or fall]. Relieving the lands and grooves at the breech created a type of progressive rifling system at the breech. When the rifle was fired, the bullet slugged up in the Rundung and was then squeezed down in the remainder of the bore. The intent was to ensure that the bullet was a tight fit in the bore. Additionally, since most of the powder fouling in the barrel occurred in the breech, the theory was that the Rundung prolonged the soldier?s ability to use his rifle before it became too fouled to load. The rifles. particularly the breech, required very careful cleaning, however, which the 1857 System Lorenz manual is positively anal about [The soldier will do. The non-commissioned officer will inspect. The officer will inspect. Etc.]. The Austrian manual notes that the beginning of the Rundung can be sensed when loading the rifle because the bullet settles much more easily on the powder from that point in the bore of the rifle. The Rundung can also be noted when cleaning ".54" caliber Muster 1854 arms, in that the patch on a cleaning rod feels looser at the breech than in the rest of the barrel. Standard American 2.5 inch [63.5 mm] square military cleaning patches will generally come off of the end of an American barracks style cleaning rod when the rod is withdrawn from the Rundung, and then have to be fished out with a worm. The wrap jag cleaning device used by the k.k. Army avoided this problem. A Federal or Confederate soldier who was not equipped with and trained to use k.k. Army cleaning equipment would have experienced difficulty in keeping the breech of his rifle clean, which undoubtedly contributed to complaints that Muster 1854 weapons quickly fouled at the breech, making them difficult to load. In rifles which were bored out to .577 inches, .58 inches, or larger, and re-rfled for the Federal Army, the Rundung would have disappeared.

Measure your bore with machinist's plug gauges, and size your "Wilkinson" [actually Lorenz] bullet no more than .001-.002 inches under that bore diameter. Using an adequate amount of powder - AT LEAST 45 grains of Swiss FFFg or 50 grains of GOEX FFFg - and lightly applied SOFT lube [I recommend MCM] the bullet will slug up just fine. Lorenz did not design these things so that a bullet starter was required.

Regards,
Don Dixon
2881V