The Firing Line Forums - View Single Post - Rookie question! .32 revolver vs .32 ACP?

James K · March 8, 2018, 10:47 PM

First, we need to understand the term "case support". In order to get uniform primer ignition (and uniform reliability and accuracy) it is necessary for a cartridge case to be supported against the blow of the firing pin. Traditionally, this was done by using the cartridge rim, which not only provided case support, but also was used for extraction of the fired case.

But, around 1900, some folks hit on the idea of a magazine fed or even an automatic or auto loading firearm. The best way to get that working well was to eliminate that pesky rim and just cut a groove in the case for extraction. But then, how to stop the case and support it against the firing pin blow? The desire to also increase the power of the cartridge led to a neat solution where the cartridge was made with a shoulder and neck - that allowed more powder space, and at the same time the shoulder provided for case support and ease of feeding. That worked well and when the idea of an auto loading pistol came along, the natural step was to make he cartridge with a bottle neck, copying the rifle cartridge design of the era.

But the pistol cartridge had a lot less space for powder and that limited its potential power. Two designers, on opposite sides of the Atlantic, found themselves with the same problem. John Browning simply could not figure out how to get proper support as well as extraction for an auto pistol cartridge any other way than by using the rim, so he reduced the rim to a minimum consistent with reliable feeding. In the meantime, one Georg Luger, in Germany, had a problem of a slightly different kind. He had a pistol which worked OK with a cartridge having a shoulder (7.65mm Parabellum), but his government wanted a pistol of a bigger caliber and redesigning the current model for a larger overall cartridge meant years of work. But simply loading a larger diameter bullet meant no shoulder was possible (though he tried), so he decided to support the case on its mouth, using case tension and careful chambering to avoid the deep crimp hitherto used at the case mouth.

Browning, meanwhile, continued on the path to the minimum rim size, and his .25 ACP (Automatic Colt Pistol), .32 ACP, 9mm Long, and .38 ACP all were produced with small but effective rims, at the cost of some feeding problems.

But, at some point, possibly during one of the early U.S. auto pistol trials, Browning encountered the 9mm Parabellum (the German trade name for Luger's pistol) and realized that here was a pistol cartridge that had no rim, yet which was well supported. That was the end of the tiny rim on Browning's cartridges. The two Browning cartridges designed after that, the .380 ACP and the .45 ACP, were rimless, with only an extraction groove, but no true rim.

Jim

March 8, 2018, 10:47 PM	#33
James K Member In Memoriam Join Date: March 17, 1999 Posts: 24,383	First, we need to understand the term "case support". In order to get uniform primer ignition (and uniform reliability and accuracy) it is necessary for a cartridge case to be supported against the blow of the firing pin. Traditionally, this was done by using the cartridge rim, which not only provided case support, but also was used for extraction of the fired case. But, around 1900, some folks hit on the idea of a magazine fed or even an automatic or auto loading firearm. The best way to get that working well was to eliminate that pesky rim and just cut a groove in the case for extraction. But then, how to stop the case and support it against the firing pin blow? The desire to also increase the power of the cartridge led to a neat solution where the cartridge was made with a shoulder and neck - that allowed more powder space, and at the same time the shoulder provided for case support and ease of feeding. That worked well and when the idea of an auto loading pistol came along, the natural step was to make he cartridge with a bottle neck, copying the rifle cartridge design of the era. But the pistol cartridge had a lot less space for powder and that limited its potential power. Two designers, on opposite sides of the Atlantic, found themselves with the same problem. John Browning simply could not figure out how to get proper support as well as extraction for an auto pistol cartridge any other way than by using the rim, so he reduced the rim to a minimum consistent with reliable feeding. In the meantime, one Georg Luger, in Germany, had a problem of a slightly different kind. He had a pistol which worked OK with a cartridge having a shoulder (7.65mm Parabellum), but his government wanted a pistol of a bigger caliber and redesigning the current model for a larger overall cartridge meant years of work. But simply loading a larger diameter bullet meant no shoulder was possible (though he tried), so he decided to support the case on its mouth, using case tension and careful chambering to avoid the deep crimp hitherto used at the case mouth. Browning, meanwhile, continued on the path to the minimum rim size, and his .25 ACP (Automatic Colt Pistol), .32 ACP, 9mm Long, and .38 ACP all were produced with small but effective rims, at the cost of some feeding problems. But, at some point, possibly during one of the early U.S. auto pistol trials, Browning encountered the 9mm Parabellum (the German trade name for Luger's pistol) and realized that here was a pistol cartridge that had no rim, yet which was well supported. That was the end of the tiny rim on Browning's cartridges. The two Browning cartridges designed after that, the .380 ACP and the .45 ACP, were rimless, with only an extraction groove, but no true rim. Jim