Range Report - 1891 Carcano (1896)

[RBruce]

Attachment 34126Got up at six am and headed to the range after coffee and loading the truck. Set up a target and settled in at the 25 yd sighting line. Aimed at the lower edge of the target and buried the front sight in the V of the rear sight. Bang! Hog Eye, as me shooting partner likes to say when the X-ring is hit. OK, yesterday after much research and discussion, I loaded three different combinations for the Carcano:
140 gr Nosler Partition with 27.3 gr IMR 4064
160 gr Hornady .268 Round Nose with 27.3 gr IMR 4064
160 gr Hornady .264 Round Nose with 27.3 gr IMR 4064

Fired a shielded test shot into the backstop while hiding behind some 2x6s just to be safe. Nothing exciting happened. Fired the first shot as described above, then two more of the 140s. (see photo) Not a bad three shot grouping for an old girl with questionable handloads - two Xs and a 10.

Next, I tried on of the Hornady 160 gr .268. Again fired behind 2x6s. It went bang, but when I went to extract the case, the bolt was locked closed. After some banging on the bolt handle, the bolt turned, but left the case in the chamber. I used a cleaning rod o remove the case. On inspection, the bolt face had made an impression on the case and the primer was cratered. I didn't fire anymore of the .268s.

Next I tried the Hornady 160 ge .264s. Fired one sighter - the hole on the edge of the 10 ring in the photo. I decided to hold off until I can get a taller front sight installed.

I think this is going to be a keeper.Attachment 34126

Information

Warning: This is a relatively older thread This discussion is older than 360 days. Some information contained in it may no longer be current.

[Patrick Chadwick]

Somewhere out there is a definitive article by David Emery on Carcano reloading. If you use the .268" bullet from Hornady, the load and type of powder are to be very critical. Basically, it is a balancing act to get just enough thrust to prevent the bullet plugging the bore without generating excessive pressure.

Some observations of my own:
I measured 10 of the Hornady .268" bullets. Using a Moore & Wright bench micrometer that has 0.0001" divisions on a 2" drum and a fiducial indicator. Not funny electronics, just high-quality mechanical engineering. The diameters, measured 1 cal. from the base, were ALL in the range 0.2671" to 0.2672", the average being 0.26715".
10 Norma Carcano bullets ranged from 0.2639" to 0.2643", the average being 0.26412"
And finally, 10 original Carcano bullets (postwar production) ranged from 0.2662" to 0.2669", the average being 0.26647".

So the average diameter of the Hornadys was only about 0.0007" larger than the average original Carcano bullet.
And in my M91/41 they perform without any problems.
HOWEVER, if you are shooting the M91 long rifle, the internal ballistics are complicated by the gain twist. If you imagine a bullet with the rifling engraved on it, then as the twist becomes sharper the engraving itself is forcibly twisted, which means considerable shear forces on the jacket. In this situation, even a slight variation in diameter is going to produce substantial variations in the shear force. It is easy to imagine that this shear tends to make the jacket lose its bond with the core, which would result in either the buller disintegrating or a catastrophic loss of accuracy if it managed to stay in one piece.

I measured the bullet diameters one caliber from the base. There is a good reason for this. I observed that the older Carcano bullets had an open base (no jacket covering) , and the diameter right on the base was a tiny bit larger. This may be more accident than design, but it has the effect that the base can obturate a tiny bit when the bullet is fired, thus achieving a better fit to the rifling with the original bullets than one would expect from the diameter of an unfired bullet. In effect, a tiny driving band is generated at the base.

Conclusions:
The original Carcano bullet is about 0.002" larger in diameter than a modern 0.264" bullet.
The flat base probably assisted the internal ballistics by bumping up a fraction of a thou when fired.
A modern 0.264", especially a boat-tail, is thus not the ideal projectile.
The (nominal) 0.268" Hornady bullet is the wrong answer to the problem, especially in rifles with a gain twist, as the driving force (and hence the pressure) required to force the bullet into the lands and further distort it as the twist progresses is considerably increased by the oversize cylindrical section.
So flat based bullets will perform better than boat tails.
Open flat-base bullets (no jacket) will perform better still.

All, of course, my own opinions. Comments welcomed.


Patrick

[RBruce]

Patrick,
Thank you for a very detailed explanation of the various forces and factors that must be considered when reloading for the early 1891 Carcanos. You descriptions and conclusions make sense to me. I need to try a fat based bullet, although the boat-tailed one did reasonably well. Thanks again. --RBS

[Parashooter]

One of Hornady's early data sheets on the .268" bullet. Note the caution against reduced loads.

[Patrick Chadwick]

Thanks Parashooter!
That is precisely the handwritten data sheet I referred to earlier, without being able to find it myself. If I remember correctly, this data sheet was composed by David Emary (or is it Emery?) for Hornady, and what bothers me is that, as far as I am aware, this data never made it into a printed recommendation from Hornady itself.

Note the narrow ranges of the powder weights - the balancing act between providing enough thrust to ensure that the oversize bullet is forced through the rifling and does not just plug the barrel, and providing so much thrust that direct overpressure from the powder burn causes a hazard.

I find the old Carcano bullets with the slight rim on the open base that (presumably) upsets to form a small driving band to be ballistically more convincing - and less hazardous!


Patrick

[jmoore]

I find the old Carcano bullets with the slight rim on the open base that (presumably) upsets to form a small driving band to be ballistically more convincing - and less hazardous!

Winchester must have thought so, too, as the bullet made for the .264 Winchester Magnum was designed as a dual diameter projectile. Bore riding dia. up front with a groove diameter section at the rear. Good luck finding any "loose", though.

The data table above is what is more or less ended up in the Hornady manual. But, like you, I have noted that the bullets currently sold are NOT 0.2676" Diameter. Significant? Dunno. Hornady seems to have used both 0.268" and 0.267" when referring to the Carcano projectile.

But the maximum military bullet dia. of 0.2669" is so close to the current Hornady size (0.2672"), it seems that some other factor in the bullet's construction would be to blame for a run up in pressures.

[Parashooter]

As described by Emary in an article apparently no longer available on the web (formerly at http://personal.stevens.edu/~gliberat/carcano/emary.html ), the mechanism behind the pressure anomalies is that the bullet has to be driven into the lands with sufficient force to engrave without hesitation. Reduced charges that fail this requirement allow the bullet to hesitate upon reaching the end of the long Carcano throat, producing a hazardous pressure spike.

[RBruce]

Durn. I printed that page by Emary some time ago, then forgot about it. I was using the Hornady load data from my set of books which lists the 27.3 gr of IMR 4064 as the starting load.

[Patrick Chadwick]

Guys, please note: that table was set up for a Fucile 91/41 - the shorter rifles (NOT carbine) with new barrels that had a normal twist, NOT a gain twist.

The situation in a barrel with a gain twist is going to be somewhat trickier - because of the huge force required to screw the engraving round as the twist sharpens. I would not wish to try an oversize bullet in a gain-twist barrel!

Patrick

[vintage hunter]

Just where exactly does it say this data is not to be used in gain twist barrels? Why produce data that is only safe to use in just one of a dozen or so firearm variants chambered for the same cartridge then neglect to include this information in the hand written warnings at the bottom of the sheet? To date I've put 200 or so rounds loaded using this data through an M1938 short rifle w/gain twist and without a single issue of any kind.