1930 to 1950: small caliber ammo for the SMGs and pistols? (2 Viewers)

[tomo pauk]

Or - just how small a cartridge will still be judged as good/worthwhile in that time period? It should be efficient to at least 150 meters from a SMG, and even better if it can do he job up to 200m.
The advantages are similar when the intermediate cartridges are compared to the full-power rounds: more rounds carried for the same weight, lower price of a single cartridge, much lower recoil, going to perhaps 40 rds in a stick mag, or 100+ in a drum. Both the SMG and pistol can be smaller and lighter than the historical weapons of the day.
Assumes that the militaries of the day are open to a new cartridge.

 

[Shortround6]

We can look at the one historical cartridge and several modern cartridges that will fill the bill.
We also need to look at the actual requirements. Getting a small bullet to 200 meters is easy. Having it get there and do what is wanted is another.

7.65×20mm Long - Wikipedia

en.wikipedia.org

Soviet 7.62x25mm, French 7.65 Long, Japanese 8mm Nambu, British .380 Revolver, German (and others) 9mm Parabellum, U.S. .45 ACP and British .455 Webley.

As can be seen, only the French 7.65 is actually smaller in case size and will allow for smaller magazines or larger capacity for the same size magazine.
French used a 77 grain bullet at about the same speed as a 9mm Parabellum fired a 124 grain bullet. The 7.62 Soviet(7/63 Mauser) uses a 85-90 grain bullet about 60m/s faster.
Some soviet Sub machine gun rounds may have been loaded hotter.
Going smaller than 7.65 means even lighter bullets and short stumpy bullets don't do well at long range, Long range here being 150-200 meters.

S&W and Federal cartridge have teamed up for the .30 Super Carry

.30 Super Carry - Wikipedia

en.wikipedia.org

of much better performance. But it uses a bullet closer in weight to the standard 9mm bullets and it operates at military rifle pressures. You need good tolerances and good materials in the guns.
You can use a bottle neck case with 5.56-6.5 bullets but you are going to need high pressures and even with pointy bullets the 150-200m performance may be lacking.

.45 Auto, .40 cal, 9x19mm and the FN 5.7x28 used in the FN MP90 and several pistols. The pistols have long, awkward grips.
The 5.7 bullets are around 30 grains but the commercial ammo varies as some of the Military stuff is considered armor piercing against body armor and is illegal in many countries or US states.

Hope this helps

 

[Elan Vital]

Regarding the 7.65 Longue adopted in 1925 (actually derived from .30 Pedersen), the report from the Versailles proving grounds summed up the matter:

« Ce choix était justifié par des performances à peu près identiques à la 9 mm Parabellum sur le plan de la précision et de la perforation jusqu'à 600 mètres pour un poids plus faible de la 7,65 mm Long (9,3 g contre 12,2 g pour la cartouche de 9 mm Parabellum). Cette différence de poids permet d'augmenter d'un tiers l'approvisionnement en cartouches de 7,65 mm par rapport à celles de 9 mm pour un poids déterminé.
D'autre part, en raison des réactions moindres qu'elle imprime à l'arme, la cartouche de 7,65 mm permet de diminuer le poids du pistolet de 200 à 300 grammes ».

"The choice was justified by nearly-identical performance to 9 mm Parabellum in terms of accuracy and perforation up to 600 meters for a reduced bullet weight (9.3g against 12.2g for 9mm). This weight difference allows an increase in ammo capacity by 1/3rd for a given weight. Moreover, due to reduced reactions on the weapon, the 7.65mm cartridge can allow weight reduction of the weapon by 200-300 grams."

At the time the choice was made, 9mm was far from ubiquitous as it was only made in Germany while 7.65mm could be quickly produced in the US which was a favored supplier since WW1. It is only with the democratization of 9mm caliber in the 30s that ammo commonality became a big factor.

 

[tomo pauk]

As can be seen, only the French 7.65 is actually smaller in case size and will allow for smaller magazines or larger capacity for the same size magazine.
French used a 77 grain bullet at about the same speed as a 9mm Parabellum fired a 124 grain bullet. The 7.62 Soviet(7/63 Mauser) uses a 85-90 grain bullet about 60m/s faster.
Some soviet Sub machine gun rounds may have been loaded hotter.
Going smaller than 7.65 means even lighter bullets and short stumpy bullets don't do well at long range, Long range here being 150-200 meters.

S&W and Federal cartridge have teamed up for the .30 Super Carry

.30 Super Carry - Wikipedia

en.wikipedia.org

of much better performance. But it uses a bullet closer in weight to the standard 9mm bullets and it operates at military rifle pressures. You need good tolerances and good materials in the guns.

The in-between cartridge between the French and the Soviet ones would've been interesting. IOW, something that does ~400J from a pistol instead of ~300 and ~500J for the two cartridges compared.

You can use a bottle neck case with 5.56-6.5 bullets but you are going to need high pressures and even with pointy bullets the 150-200m performance may be lacking.
.45 Auto, .40 cal, 9x19mm and the FN 5.7x28 used in the FN MP90 and several pistols. The pistols have long, awkward grips.

A good thing might've been not-overdoing the things. A cartridge for 5.5-6mm bullets that starts out from a 7.5-8 mm cartridge would've both kept the length in the check, allow high MVs, and still be practical for the double-stack magazines.
BTW - the .45 ACP in a double stack magazine would've also puched the grip size from comfortable to perhaps awkwards, especially in the 1930s when the knowledge and materials to make grips as thin as possible while also being as strong was not there.

For the Americans - I'd suggest trying it out with the .38 Super, as well as with the aforementioned in-between 7.62.