30-08-2014, 05:07 AM
(This post was last modified: 05-09-2014, 07:21 PM by Bob Prudhomme.)
As promised, here is the next installment of how the 6.5mm Carcano rifles received a reputation as inaccurate rifles. Thanks for posting the pics of the bases of the cartridges, Drew.
The 6.5x52mm Model 91 Carcano long rifle was, as the model indicates, introduced in 1891. It was during a transition period in Europe that saw European armies abandoning the idea of a large calibre, low velocity black powder rifle in favor of a small calibre, high velocity rifle using smokeless powder. Many ideas were copied from rifle to rifle, such as the Mannlicher "en bloc" clip used in the Carcano and the Mauser type bolt that utilized two locking lugs. Suffice it to say that, with all of the sharing (and stealing) of ideas, the rifles that entered the First World War were all pretty much equal in design, and it would be difficult to claim that one was more accurate than the other.
The 6.5mm Carcano M91 long rifle design did incorporate two features that were not seen in very many other rifles, if at all, and the jury is still out on whether these features made the M91 more or less accurate than other rifles.
The first is the rifling grooves in the barrel. While maintaining the same 6.5 mm (.256") calibre (bore) as other 6.5mm rifles, the Carcano designers elected to make their rifling grooves deeper. This required a unique, wider bullet for the Carcano that measured .268" in diameter, as opposed to the standard bullet for other 6.5mm rifles that measured .264" in diameter.
The deeper rifling grooves may have been the reason for the second unique design feature of the Carcano. Instead of the rifling grooves in the barrel being made at a standard rate of twist (ie. 1:8 or 1:9), the Carcano riflings were made with what is known as "progressive" or "gain" twist. The riflings began, at the breech (chamber) at a gentle rate of twist of 1:22.79 (one complete turn in every 22.79 inches of barrel length) and got progressively tighter towards the muzzle, ending with a rate of twist of 1:7.939. It was believed, and very well may be true, that this type of rifling enhanced accuracy and reduced barrel wear by giving the bullet a chance to build up its spin slowly and gently. Unfortunately, it was also complex and expensive to machine, compared to standard riflings, and led to critical supply shortages of Carcano rifles in WWI.
Now, as the M91 barrel was almost 31 inches long, which aided in muzzle velocity and accuracy, it soon became apparent that not all soldiers needed such a long rifle for bayonet charges, and that some troops would be far better off with a much shorter carbine version of the M91, such as cavalry, mounted infantry, artillery, scouts and support troops. Fighting against the Austrians in steep mountainous country in WWI also proved the disadvantages of an extremely long rifle.
In 1893, the first carbine was introduced, the M91 Cavalry carbine or Moschetto Modello 91 da Cavalleria. While many of these were manufactured as new rifles, a practice began in the 1890's of simply cutting the 31 inch barrel of a long rifle down to the 17 inch carbine length. The next carbine was the Model 1891 T.S. (Truppe Speciali or Special Troops), begun in 1898. These were all manufactured as new rifles, evidenced by their stocks. Many of the cavalry carbine stocks were plainly cut off long rifle stocks.
These two carbines were the standard through WWI, and nothing much changed until 1924, with the introduction of the Model 91/24 carbine. This one model of carbine alone likely did far more to tarnish the reputation of Carcano rifles in general than any other factor. The 1920's were not the best of economic times for Italy and Italian arms makers, ever seeking corners to cut, expanded on the bad idea started with the Cavalry carbine.
From 1924 to 1929, approximately 260,000 M1891 long rifles were converted into T.S. pattern carbines. As with the conversions in the 1890's, long rifle barrels were cut from 31 inches to 17 inches and the muzzles re-crowned. If this were done to rifles with standard riflings, performance, muzzle velocity and accuracy may have suffered somewhat but, in a rifle with progressive twist rifling, this practice was an absolute disaster.
As I stated earlier, the riflings in a M91 long rifle begin, at the breech, at a gentle rate of twist of 1:22.79 (one complete turn in 22.79 inches of barrel length), and progressively get tighter until the rate of twist, at the muzzle, is 1:7.939. In other words, the designers of the Carcano bullet believed a final rate of twist of at least 1:8 was needed to impart enough spin to the bullet in order to maintain gyroscopic stability on its way to the target. By removing 14 inches of the tightest riflings from a 31 inch barrel, the bullets simply were not spinning fast enough. These carbines couldn't hit a barn from the inside, and there is still debate about whether or not the term "Humanitarian Rifle" applied to these carbines as well or just to the bullets.
Speaking of bullets, Italian military issue rifle cartridges for the Carcanos had some serious problems, too, and their contribution to the reputation for inaccuracy is next.
The 6.5x52mm Model 91 Carcano long rifle was, as the model indicates, introduced in 1891. It was during a transition period in Europe that saw European armies abandoning the idea of a large calibre, low velocity black powder rifle in favor of a small calibre, high velocity rifle using smokeless powder. Many ideas were copied from rifle to rifle, such as the Mannlicher "en bloc" clip used in the Carcano and the Mauser type bolt that utilized two locking lugs. Suffice it to say that, with all of the sharing (and stealing) of ideas, the rifles that entered the First World War were all pretty much equal in design, and it would be difficult to claim that one was more accurate than the other.
The 6.5mm Carcano M91 long rifle design did incorporate two features that were not seen in very many other rifles, if at all, and the jury is still out on whether these features made the M91 more or less accurate than other rifles.
The first is the rifling grooves in the barrel. While maintaining the same 6.5 mm (.256") calibre (bore) as other 6.5mm rifles, the Carcano designers elected to make their rifling grooves deeper. This required a unique, wider bullet for the Carcano that measured .268" in diameter, as opposed to the standard bullet for other 6.5mm rifles that measured .264" in diameter.
The deeper rifling grooves may have been the reason for the second unique design feature of the Carcano. Instead of the rifling grooves in the barrel being made at a standard rate of twist (ie. 1:8 or 1:9), the Carcano riflings were made with what is known as "progressive" or "gain" twist. The riflings began, at the breech (chamber) at a gentle rate of twist of 1:22.79 (one complete turn in every 22.79 inches of barrel length) and got progressively tighter towards the muzzle, ending with a rate of twist of 1:7.939. It was believed, and very well may be true, that this type of rifling enhanced accuracy and reduced barrel wear by giving the bullet a chance to build up its spin slowly and gently. Unfortunately, it was also complex and expensive to machine, compared to standard riflings, and led to critical supply shortages of Carcano rifles in WWI.
Now, as the M91 barrel was almost 31 inches long, which aided in muzzle velocity and accuracy, it soon became apparent that not all soldiers needed such a long rifle for bayonet charges, and that some troops would be far better off with a much shorter carbine version of the M91, such as cavalry, mounted infantry, artillery, scouts and support troops. Fighting against the Austrians in steep mountainous country in WWI also proved the disadvantages of an extremely long rifle.
In 1893, the first carbine was introduced, the M91 Cavalry carbine or Moschetto Modello 91 da Cavalleria. While many of these were manufactured as new rifles, a practice began in the 1890's of simply cutting the 31 inch barrel of a long rifle down to the 17 inch carbine length. The next carbine was the Model 1891 T.S. (Truppe Speciali or Special Troops), begun in 1898. These were all manufactured as new rifles, evidenced by their stocks. Many of the cavalry carbine stocks were plainly cut off long rifle stocks.
These two carbines were the standard through WWI, and nothing much changed until 1924, with the introduction of the Model 91/24 carbine. This one model of carbine alone likely did far more to tarnish the reputation of Carcano rifles in general than any other factor. The 1920's were not the best of economic times for Italy and Italian arms makers, ever seeking corners to cut, expanded on the bad idea started with the Cavalry carbine.
From 1924 to 1929, approximately 260,000 M1891 long rifles were converted into T.S. pattern carbines. As with the conversions in the 1890's, long rifle barrels were cut from 31 inches to 17 inches and the muzzles re-crowned. If this were done to rifles with standard riflings, performance, muzzle velocity and accuracy may have suffered somewhat but, in a rifle with progressive twist rifling, this practice was an absolute disaster.
As I stated earlier, the riflings in a M91 long rifle begin, at the breech, at a gentle rate of twist of 1:22.79 (one complete turn in 22.79 inches of barrel length), and progressively get tighter until the rate of twist, at the muzzle, is 1:7.939. In other words, the designers of the Carcano bullet believed a final rate of twist of at least 1:8 was needed to impart enough spin to the bullet in order to maintain gyroscopic stability on its way to the target. By removing 14 inches of the tightest riflings from a 31 inch barrel, the bullets simply were not spinning fast enough. These carbines couldn't hit a barn from the inside, and there is still debate about whether or not the term "Humanitarian Rifle" applied to these carbines as well or just to the bullets.
Speaking of bullets, Italian military issue rifle cartridges for the Carcanos had some serious problems, too, and their contribution to the reputation for inaccuracy is next.
Mr. HILL. The right rear portion of his head was missing. It was lying in the rear seat of the car. His brain was exposed. There was blood and bits of brain all over the entire rear portion of the car. Mrs. Kennedy was completely covered with blood. There was so much blood you could not tell if there had been any other wound or not, except for the one large gaping wound in the right rear portion of the head.
Warren Commission testimony of Secret Service Agent Clinton J. Hill, 1964
Warren Commission testimony of Secret Service Agent Clinton J. Hill, 1964