Model 41 Carcano Reloading Help!!

[Patrick Chadwick]

I have been pondering on how to load "Roma", my "bella figura" Fucile 91/42.
The best results in my limited testing to date were with 31 gns of RL 15 behind the Hornady bullets marked on the box as 0.268", but which are not 0.268". The results with Norma ammo were dire.

Having read a lot about the Carcano bore question, I measured the bullet diameter on some samples of original ammo, Norma ammo, and Hornady bullets:

Original: (2 clips)
0.2662
0.2664
0.2665
0.2664
0.2665
0.2666
0.2667
0.2665
0.2662
0.2663
0.2664
0.2669 (yes, I checked that one again!)


Norma:
0.2640
0.2639
0.2641
0.2642
0.2641
0.2640
0.2642
0.2642
0.2642
0.2643

Hornady
0.2672
0.2671
0.2671
0.2671
0.2671
0.2672
0.2671
0.2672
0.2672
0.2672

If I have done the maths correctly, then:

Average for Norma: 0.26412
Average for original: 0.26647
Average for Hornady: 0.26715

These measurements were NOT made with a DIY-market micrometer, but with a Moore & Wright bench micrometer with a fiducial indicator that really does have 1/10000" scale marks.

So what do I conclude from the above? - That, at least for my box, the Hornady bullet has an extremely narrow variation in a diameter that is actually a gnat's whisker over 0.267", regardless of what is printed on the box. (Thought: I wonder if Hornady reduced the diameter from 0.268" without telling us?).

Furthermore, this diameter is only 0.0005" above the original Carcano samples. In fact, it would seem to be only half a gnat's whisker larger than the upper range of the Carcano bullets. In many cases, it is probably closer to the original bullet diameter than a worn bore is to the original bore diameter.

So I reckon that the Hornady bullet is OK for real-life milsurps that are a bit worn. But I would not wish to push my luck, and so, as always, I seat my bullets so that they are clear of the lands (about 0.2 mm = 0.008") to avoid any extra pressure from bullets being pressed into the throat when chambered. In the past, I have read some fairly implausible stuff from people who claim to seat their bullets as close as 0.003" to the lands. Well, they are presumably unaware of the simple fact that brass has a much higher coefficient of expansion than steel. And I presume that they have bullets and reloading setups with tighter tolerances than I can measure with a bench micrometer. So real-life seating tolerances plus warm ammo taken out of your pocket and chambered in a cold rifle could mean that the 0.003" has disappeared or even become negative. Or maybe they keep both rifle and ammo at a constant temperature...or heat up the rifle before loading the first shot on a cold day?

So clean the barrel properly, removing any copper or lead fouling, keep the Hornadys clear of the lands, follow the table presented above, and it all should work. It does for me.


Patrick

[jmoore]

I wonder if there's lot to lot variation or if it's possible that there's enough temperature induced change to account for the range in sizes? My mircmeters must be calibrated throughout their range at least once a year by a metrology lab, so the mikes ought to be OK. I have posted previously sizes of 0.2673" and 0.2675" in different threads, including this one:

More 6.5 Carcano fun coming!

So, maybe lot variations? Probably not significant. It's not uncommon to find military bullets that vary more in diameter around the circumference of one bullet!

---------- Post added at 02:44 AM ---------- Previous post was at 02:38 AM ----------


An old photo of a sample measurement of a milsurp bullet.

[Patrick Chadwick]

that there's enough temperature induced change to account for the range in sizes?

That is certainly not the explanation in this case. All components and the bench micrometer were, of course, at the same temperature of around 20 degrees C, having been in the same room (in fact on the same bench) for months. But you are right to point it out. I also have a Mitutoyo measuring head that reads to 1 micron. that is, in inch terms, truly 5/8 of F.A. To use this sensibly, you need to have all surfaces clean and dry, and must avoid touching the items being measured as far as possible, And have all components at a constant known temperature. And avoid draughts etc. etc. And wear clean gloves, otherwise your have a device that is in effect measuring temperature changes and surface dirt.

The point I wanted to make (among others) is that if you get into serious measurement, you realize that the "I set my bullets a couple of thou off the lands" stuff is an empty claim unless the claimants are using much more sophisticated measuring equipment than that used by the typical reloader AND keep and use cartridges and gun at constant temperatures. An aim that is invalidated as soon as you fire the first shot! You personally will be aware that just because one can read an instrument to a certain level of resolution, that does not mean that the instrument is accurate to the same level. But many people are not aware of this.

Time to stop banging on about this bee in my bonnet - I have a lot of hungry muzzles to feed!


Patrick

[Patrick Chadwick]

I wonder if there's lot to lot variation

Quite possibly, but all sample groups were from the same package.

[jmoore]

As for the variations in size due to temperature, I was pondering the variances between yours and mine, and mine at different times. Not so much the variations in each bullet. We used to have a 400 lb micrometer in the metrology lab that had an optical viewer which would show a test piece grow in real time as you placed a finger on it for a few seconds. I forget exact specs, it was 1986 or so..

In this case not so much that the bulets would change size, but the micrometers themselves. (I don't measure bullets in temperature controlled environments.)

[Patrick Chadwick]

We used to have a 400 lb micrometer in the metrology lab that had an optical viewer which would show a test piece grow in real time as you placed a finger on it for a few seconds.

Must have been down at the micro-inch level. Definitely the sort of thing that can detect draughts!


Patrick

[jmoore]

I do deal with this sort of thing on a daily basis: Yesterday, finish machining a 15"+ diameter, ~0.100" wall thickness, with a nickel alloy plasma spray coating. Part WILL shrink 0.001"-0.003" depending on several factors all dealing with the amount of heat that gets into the part. So, since it has a 0.002" tolerance, cut it 2 over and then, ahem, wait for the part to stabilize. (Waiting often involves doing posts like this one!) If you get in a hurry, it won't pass either the second set of eyes or final inspect. Haste definitely makes waste in this case!

Today, running a 26" part on the gap bed that requires a tubular framed mic. to minimize gravity distortion of the micrometer's frame whilst in the upright position. Part "only" runs at 10,000+ RPM in service so getting the size (and runout!) right makes a tiny amount of difference...

Where were we??? Oh, yeah, Carcano bullets. And M41s

IIRC the M41 is the only Carcano with conventional rifling. The rest are gain twist with some designed in groove taper. All so carefully thought out, you'd think they would have put some super duper sights on 'em. (Too expensive, I guess.)

[vintage hunter]

JM, do you mean the M41 is the only Carcano chambered in 6.5 to have conventional rifling? I believe that the 7.35x51 variants have conventional rifling too, or did I miss something?

[jmoore]

JM, do you mean the M41 is the only Carcano chambered in 6.5 to have conventional rifling? I believe that the 7.35x51 variants have conventional rifling too, or did I miss something?

You answered your own question I think! I omitted the 7,35 without thinking about it one way or the other. 6,5s on the brain!

[concretus]

Well I slugged the bore yesterday and it come out right at .267". So now is follow the recipes with the correct primer and minimum charge.