12,7x81SR

A blink of Swedish history...

The 12,7 mm sk ptr m/40 cartridge were in active service in between 1940 until 1945. It is still in the files until around 1950 before finally phased out. The reason behind the limited time frame is that the ammunition were used in only two models of aircrafts in service for only 5 years. The aircrafts were bought in the aftermath of the purchase of four navy ships from Italy in 1940.


The two imported aircrafts were of the models:

J11/Fiat Aeuronautica d'Italia/Fiat CR 42 regarding 72 aircraft in service. The first 12 aircrafts were delivered in April 1940 and at first stationed in F3, Malmen outside Linköping as reconnaissance aircrafts. These planes were intended for Finland, but when the first winter war ended in 1940, the planes were bought by Sweden as Finland were in greater need of capital than aircrafts at that time.
When a second order of 60 planes arrived shortly after, all airplanes were to be stationed in F9, Säve, not far from Gothenburg on the west coast.
The bi winged aircrafts were unmodern already at the delivery, but were what could be purchased at the time.
The J11 aircrafts were discontinued in 1945.

J20/Caproni Re 2000 FALCO 1, regarding 60 aircrafts in use between 1941-1945. All airplanes were stationed at F10, Bulltofta outside Malmö in the south of Sweden.


The weapons used were designated "12,7 mm automatic cannon m/40" and were of the model Breda-SAFAT (Societa Anonima Fabrica Armi Torino) chambered for the 12,7x81SR Breda ammunition. The rate of fire were in the area of 700 RPM, and the velocity around 760mps. The ammunition were fed with a for the calibre specific metallic disintegrating link designated "12,7 mm länk m/40".

There are four types of ammunition identified to of been used in Sweden, but there cannot be ruled out that further types might of been used that has not been found yet.
No 12,7x81SR ammunition were produced in Sweden, the available sources state Italy as the sole manufactured and supplier.

The Italian colour marking were kept without modifications to Swedish signature.
12,7 mm sk ptr m/40 slprj m/40 (Tracer, red tip)
12,7 mm sk ptr m/40 pbprj m/40 (Armour piercing, green tip)
12,7 mm sk ptr m/40 brprj m/40 (Incendiary, blue tip)
12,7 mm sk ptr m/40 öprj m/40 (Ball, no colour)

There is also a inert exercise cartridge. The projectile is green and do then follow the Swedish standards, but I cannot say if it was green on the delivery or painted so locally.


In November of 1941, SAN declared that the ammunition were in good supply, and that is in the level of 800 000 rounds. As the air force had 144 PCS of 12,7 mm automatic canon m/40 in stock at that time, it equals around 5 500 rounds per weapon.

The stock of weapons and ammunition increased in 1942. Both the J11 and the J20 Aircraft hade two automatic cannon m/40 each, giving a inventory of 264 pcs (any spares not counted for). There were around 2 500 000 rounds on stock in the autumn 1942, equals 9 400 rounds per weapon, or 4 700 rounds per aircraft. There were never any intention to produce the ammunition locally, and I guess it is due to the limited number of guns and aircrafts using this calibre and also the status of the airplanes, as considered outdated already at delivery.

Both of the aircrafts had their 12,7 mm automatic cannon m/40 mounted in the body of the aircraft, using synchronisation to shoot within the propeller area. The construction were less than satisfactory and there are many reports of propeller damage when using the weapons. Even if there were several tests and trials to determine if it were due to the ammunition or the synchronisation, the conclusion were never fully settled. Different batches were tested at Provskjutningscentralen i Karlsborg, and there were found to deliver variations in the velocity. Some ammunition were also found to have the wrong length. The ammunition were revised to work as intended.

As the ammunition were not considered to be well produced and also uneven in quality, a inquiry were made by Kungliga Flygförvaltningen to Statens Krigsmaterielnämnd to renovate 2 500 000 rounds. The inquiry were answered by a offer sent 25 of July 1942. Ammunitionsfabriken Karlsborg were found suitable to perform the task. At the location they had the facilities, staff and knowledge needed. There were two alternatives presented:

1st alternative:
For a expected total cost of renovation of 275 000 SEK, or 0,11 SEK per round. This under the circumstances that Italian primers is delivered free of charge to the factory, and that the powder can be reused.
The capacity is about 10 000 rounds per day (2 shifts of 8 hour)
A start could be performed in a month time.

2nd alternative:
For a expected total cost of renovation of 300 000 SEK or 0,12 SEK per round. In this calculation is included primers (Fulminate of mercury), to be produced locally at Karlsborg. Powder is to be reused.
The capacity is as in alternative 1, but the start time is pushed out to around 2 month.

The revision were ordered 5th of September, 1942. The chosen alternative is still unknown.


References:
Alla tiders flyg, ISBN 91-971270-7-8
Att flyga är att leva, Gösta Norrbohm, Bertil Skogsberg
Flygvapnets Eldvapenammunition 1949, textbilaga till bildbandet
Archived letters from Kungliga Flygförvaltningen, 1941.