7.35x51 Performance


#1

Listed performance of the 7.35x51 Italian on Max’s and Tony’s sites is a 128gr (8.3g) bullet at 2,480 ft/s (756 m/s). This is remarkably low performance, barely higher than 7.62x39!

It’s not difficult for me to believe that the cartridge was that low-powered, however a couple of questions are raised in my mind.

First, why would the Italians use such a large case to attain such modest performance? It’s clear that they knew the benefits of shorter ammunition, and experimental versions of the 7.35mm cartridge had case lengths as short as 41mm!

Further, it seems that the case is loaded with 40 grains of stick propellant, as can be seen here. 7.62x39 uses about 30 grains of propellant to attain similar performance, while 40 grains is close to the powder charges for .303 British or .300 Savage (both of which are very comparable in size). In addition, the reloading data seen in that blog post also points to some discrepancy, as with only 37 grains of powder the author attained performance almost 300 feet per second better than the listed performance for the military load (with 22% greater energy) from the same 21" barreled Carcano carbine.

Obviously, different propellants will have different characteristics, and different charge weights can produce the same velocity, depending on their burn rates and other things. However, that doesn’t seem to fully account for what is seen here.

So, three theories as to what might be going on:

  1. The listed powder charge in that blog post is wrong.

  2. The commonly listed velocity on Max and Tony’s websites is wrong.

  3. The Italians used very inefficient powders.

Can anyone help me out with this?


#2

Factor in the strength of the weakest rifle that could have used that ammunition and you may have one part of the puzzle answered.

Ray


#3

Tau, I took this information from an Italian document dated 1938:

7.35 mm Mod. 38:

Bullet weight: 8.30 g
Propellant weight: 2.62 g
Muzzle velocity: 757 m/s
Pressure: 2570 atm

6.5 mm Mod. 91:

Bullet weight: 10.35 g
Propellant weight: 2.28 g
Muzzle velocity: 700 m/s
Pressure: 3200 atm


#4

Fede;

That is pretty compelling evidence, to me! Looks like the cartridge is just very low pressure (comparable to 7.62x39), and the Italian propellant is just volumetrically-speaking very inefficient. Thanks for posting that; do you happen to have a scan of the original document?


#5

Ray: If the power of the 7.35 m/m cartridge was limited by the arms in which it might have been used, then it isn’t the Carcano which was the problem, but rather the squad LMG with which it would have been paired, the Breda M30. The Carcano was actually pretty robust, but the Breda had a poor reputation for utility and reliability. Jack


#6


#7

I think that the original 6.5 carcano loaded with Solenite ( and even older cartridges loaded with balistite) was also tamed in order to be fired in barrels with a progressive twist. You need low pressure loads in order to avoid dangerous pressure peaks when firing.

The powder type wasn’t changed when italians adopted rifles with standard twist rifling or the large caliber. The Solentite fullfilled the case up to the base of the bullet, so you actually can’t increase the performance without using another powder type.


#8

I have to agree with Jack, but from a different perspective. I have always been told that the Carcano is a weak action, but since they are or were cheap, I have ended up with half a dozen of them. I took a machine shop class at the local community college and tried to convert one of my pre-butchered Carcanos to 7.62x39. I never got the job finished, but in examining the bolt head, I noticed that the bearing surface of one of the locking lugs was rusty and the other lug looked polished. Obviously one bolt lug was doing all of the work. I showed it to my instructor, and he explained that parts that could possibly be subject to a life threatening failure are usually engineered for at least four, and more likely eight times the calculated strength requirement.

I went home and checked my other Carcanos. Only one, from 1918, had anything that resembled even minimal engagement of both lugs, with one lug fully polished and about half the bearing surface polished at the leading edge of the lug. The others were either rusted over or appeared to show tool marks (as apposed to scratches). I have shot all of these guns without problems. I have read that PO Ackley tested Carcanos to failure and did not agree with the “weak” assessment of other authorities. Perhaps the low pressures of Carcano ammunition reflect the known realities of Italian rifle manufacturing or perhaps the Italians were beginning to understand the drawbacks of overpowered rifle cartridges for less than well trained infantrymen.


#9

It is not uncommon at all for all locking lugs on a bolt for a rifle to not bear in its receiver recess. A test years ago verified that - I wish I could recall where the test results were published and who did them, but it is before I was saving virtually everything I read on guns and ammo. A Weatherby Mark V having, as I recall, nine rather small locking locks on the bolt head, was bearing on less than half of them. Still, I sold Weatherby rifles for years with nary a problem with them, other than wood stocks splitting behind the receiver tang on the big calibers (.378 WM and .460 WM).


#10

If Ackley tested the Carcano it was after his well-known test series in the immediate post-1945 period. The results of those experimental firings are found in Roy Dunlap’s Ordnance Went Up Front and, probably, elsewhere. There have been other controlled tests, however, in which the specific specimens tested held up as well as could have been reasonably expected. Jack


#11

If you look at the rifle (fixed rearsight) and the bullet (not a spitzer but halfway between spitzer and round-nose) I think it was the Italians intention to equip the soldier with a low-recoil cartridge that is sufficient for the relatively short ranges expected in war.

Any weakness of the LMG cannot be the reason, because it also fired the more powerful 6.5 mm. The propellant was in my view chosen to have no big void in the case.


#12

I have been told by an Italian with an interest in arms history that the reason for the development of the 7.35mm, rather than just designing a spitzer bullet for the 6.5mm (as the Japanese did) is that a large proportion of the 6.5mm Carcano barrels were shot out, with no rifling left. The Italians couldn’t afford new barrels (they were chronically short of cash) so they simply bored out the existing barrels to the larger calibre, cutting new rifling as they did so.

This would likely account for using such a low pressure, since the barrel would be thinner.


#13

According to the Italian publication dated 1938: “The determinant reason of the transformation is to be found in the evolution of tactical criteria, procedures for action and mode of use of infantry firearms, which now exclude the opportunity of shooting with a rifle beyond those distance limits that do not allow the accuracy of aiming”.

The new cartridge and rifle were made according to the following requirements: 1) Ballistic improvement over the 6.5 mm up to the distance of 4.500 m; 2) Lighter cartridge and lighter bullet; 3) Caliber between 7.5 and 8 mm [in practice, the 7.35 mm caliber was chosen because it was the maximum allowed in a worn-off barrel of 6.5 mm caliber]; 4) Keep the characteristics of M. 91 in use as much as possible (streght, rusticity, simplicity, easy assembly/dissasembly, etc.); 5) Minimal need of modification work; 6) Ensure the operation of the cartridge in the Breda M. 30 machine gun using a new barrel and without altering the mechanical quality.


#14

[quote=“XPH2USN”]I have to agree with Jack, but from a different perspective. I have always been told that the Carcano is a weak action, but since they are or were cheap, I have ended up with half a dozen of them. I took a machine shop class at the local community college and tried to convert one of my pre-butchered Carcanos to 7.62x39. I never got the job finished, but in examining the bolt head, I noticed that the bearing surface of one of the locking lugs was rusty and the other lug looked polished. Obviously one bolt lug was doing all of the work. I showed it to my instructor, and he explained that parts that could possibly be subject to a life threatening failure are usually engineered for at least four, and more likely eight times the calculated strength requirement.

I went home and checked my other Carcanos. Only one, from 1918, had anything that resembled even minimal engagement of both lugs, with one lug fully polished and about half the bearing surface polished at the leading edge of the lug. The others were either rusted over or appeared to show tool marks (as apposed to scratches). I have shot all of these guns without problems. I have read that PO Ackley tested Carcanos to failure and did not agree with the “weak” assessment of other authorities. Perhaps the low pressures of Carcano ammunition reflect the known realities of Italian rifle manufacturing or perhaps the Italians were beginning to understand the drawbacks of overpowered rifle cartridges for less than well trained infantrymen.[/quote]

[quote=“JPeelen”]If you look at the rifle (fixed rearsight) and the bullet (not a spitzer but halfway between spitzer and round-nose) I think it was the Italians intention to equip the soldier with a low-recoil cartridge that is sufficient for the relatively short ranges expected in war.

Any weakness of the LMG cannot be the reason, because it also fired the more powerful 6.5 mm. The propellant was in my view chosen to have no big void in the case.[/quote]

[quote=“Fede”]According to the Italian publication dated 1938: “The determinant reason of the transformation is to be found in the evolution of tactical criteria, procedures for action and mode of use of infantry firearms, which now exclude the opportunity of shooting with a rifle beyond those distance limits that do not allow the accuracy of aiming”.

The new cartridge and rifle were made according to the following requirements: 1) Ballistic improvement over the 6.5 mm up to the distance of 4.500 m; 2) Lighter cartridge and lighter bullet; 3) Caliber between 7.5 and 8 mm [in practice, the 7.35 mm caliber was chosen because it was the maximum allowed in a worn-off barrel of 6.5 mm caliber]; 4) Keep the characteristics of M. 91 in use as much as possible (streght, rusticity, simplicity, easy assembly/dissasembly, etc.); 5) Minimal need of modification work; 6) Ensure the operation of the cartridge in the Breda M. 30 machine gun using a new barrel and without altering the mechanical quality.[/quote]

The assessment that the Italians wanted what we would now call an “intermediate” cartridge is supported by the information contained in this thread.

[quote=“TonyWilliams”]I have been told by an Italian with an interest in arms history that the reason for the development of the 7.35mm, rather than just designing a spitzer bullet for the 6.5mm (as the Japanese did) is that a large proportion of the 6.5mm Carcano barrels were shot out, with no rifling left. The Italians couldn’t afford new barrels (they were chronically short of cash) so they simply bored out the existing barrels to the larger calibre, cutting new rifling as they did so.

This would likely account for using such a low pressure, since the barrel would be thinner.[/quote]

That doesn’t sound likely; as experiments Hatcher did shaving down M1903 barrels to extreme thinness showed that even with high pressure calibers, barrels are much heavier than they need to be from a structural perspective. Unless the Italians had far inferior metallurgy (unlikely, IMO) to the Americans, the explanation that most makes sense to me is that the Italians wanted an intermediate cartridge, and the propellant that they could make in quantity required a case that large to house it. The low peak pressure produced was most likely a byproduct of this arrangement. The same effect can be seen in .303 British; the powder fills the case completely despite the relatively low peak pressure.

Thanks for everyone’s help with this. It seems the Italians can be credited with fielding the first (purpose-designed) intermediate caliber, after all.


#15

Tau, I can’t see no relation between the development of the early short cartridges and the 7.35 mm Mod. 38. The “7.35x41” is not documented, there is no evidence that it was a predecesor of this cartridge -or the short cased cartridges- and may not even date from 1935, no matter what the headstamp says.


#16

What’s the reasoning behind this? The cartridge looks very similar to me; with the same bullet construction and case head. Is there some reason for believing it’s not genuine or not related to the 7.35x51?


#17

Tau, my reasoning is to not establish a relation or link between the development of documented cartridges, like the short cased rounds from the 1920’s and the 7.35 mm Mod. 38, and a single round of which we know nothing about. I didn’t say it is not genuine but there are several aspects of this round that I don’t like.


#18

I think I grasp your meaning, but could you elaborate?


#19

[quote=“Tau”]

[quote=“TonyWilliams”]I have been told by an Italian with an interest in arms history that the reason for the development of the 7.35mm, rather than just designing a spitzer bullet for the 6.5mm (as the Japanese did) is that a large proportion of the 6.5mm Carcano barrels were shot out, with no rifling left. The Italians couldn’t afford new barrels (they were chronically short of cash) so they simply bored out the existing barrels to the larger calibre, cutting new rifling as they did so.

This would likely account for using such a low pressure, since the barrel would be thinner.[/quote]

That doesn’t sound likely; as experiments Hatcher did shaving down M1903 barrels to extreme thinness showed that even with high pressure calibers, barrels are much heavier than they need to be from a structural perspective. Unless the Italians had far inferior metallurgy (unlikely, IMO) to the Americans, the explanation that most makes sense to me is that the Italians wanted an intermediate cartridge, and the propellant that they could make in quantity required a case that large to house it. The low peak pressure produced was most likely a byproduct of this arrangement. The same effect can be seen in .303 British; the powder fills the case completely despite the relatively low peak pressure.[/quote]

You may well be right about the pressure issue, which was merely my speculation, but the explanation for the 7.35mm calibre which I described is supported by Fede’s information.


#20

Yes, that sounds reasonable to me.