Monac
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I don't know a lot about rifle cartridges, I guess. I always thought rimless bottlenecked cartridges like 8mm Mauser headspaced on the bottleneck, not the case mouth. At least when they were originally introduced. Is that not so?
Why is the 32 acp semi-rimmed?
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Jim Watson
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Headspace control for a rimless bottleneck is the case shoulder. Mauser, Luger, and several other early auto pistols were the same as the rifles.
whughett
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I have not read this entire thread. Can some one define “rim lock” for me.
Most semi-auto cartridges are "rimless". They have a rim, but the rim is either the same diameter as the largest part of the cartridge, or it's smaller diameter. That makes feeding out of a magazine simpler because the rim is unlikely to catch on anything.
A "rimmed" cartridge has a rim that is significantly larger diameter than any other part of the cartridge. A "semi-rimmed" cartridge has a rim that is larger in diameter than any other part of the cartridge, but not much larger.
When you have a rimmed or semi-rimmed cartridge that needs to feed out of a magazine, it's important that the rim of the top round not end up behind the rim of the round that's next in the magazine or it can hang on that rim and fail to feed. That's called rim lock.
As mentioned in prior posts, if the cartridge length is a good fit for the magazine it will be shot out of, it is a non-issue. All the rims end up in pretty much the same place and there's not room for one to move forward enough for the one above it to get behind it. But when the cartridge is significantly shorter than will fit into the magazine, now there's the possibility for the top cartridge to be as far back in the mag as it will go and the cartridge below it to be as far forward as it will go which could put the rim of the top round behind the rim of the round below it.
A "rimmed" cartridge has a rim that is significantly larger diameter than any other part of the cartridge. A "semi-rimmed" cartridge has a rim that is larger in diameter than any other part of the cartridge, but not much larger.
When you have a rimmed or semi-rimmed cartridge that needs to feed out of a magazine, it's important that the rim of the top round not end up behind the rim of the round that's next in the magazine or it can hang on that rim and fail to feed. That's called rim lock.
As mentioned in prior posts, if the cartridge length is a good fit for the magazine it will be shot out of, it is a non-issue. All the rims end up in pretty much the same place and there's not room for one to move forward enough for the one above it to get behind it. But when the cartridge is significantly shorter than will fit into the magazine, now there's the possibility for the top cartridge to be as far back in the mag as it will go and the cartridge below it to be as far forward as it will go which could put the rim of the top round behind the rim of the round below it.
zaitcev
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Semi-rimmed rifle cartridges typically have a bevel on the rim that is sufficient to resolve rim-lock without any additional mechanisms such as interruptor. This is how a 6.5mm Arisaka feeds semi-rimmed cartridges from basically a Mauser magazine.
Jim Watson
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There were real Mausers with slanted magazines to preserve the advantages of the flanged cartridge, not to mention the Siamese Mauser, made in Japan.
WestKentucky
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Why is 32 Semi rimmed? Because JMB as highly regarded as he is did not ever think completely outside of the box. He kicked the box over, stood inside and looked out, but never truthfully stepped out of the box. He improved lots of things and is deserving of recognition, but I don’t hold him in as high regard as I do some others. Same goes for Sam Colt. Likely most of that was good businessmanship because who wants to sink a fortune into something new and awesome if it has risk of not selling, as opposed to something significantly improved so that you already have a prepopulated audience of investors and customers.
32 ACP was also a warhorse for a lot of European countries. Military groups are very hard shells for truly innovative items that don’t make astronomical impact. Like who would have invested in an electronically controlled bomb in 1940... risk it doesn’t work and all that time effort labor and space on the plane for control equipment is a big risk, but an atomic bomb is a game changer weapon. If you look at history in a military procurement frame of mind it’s somewhat amazing that we have advanced as far as we have.... brass cartridge rifles WERE available before the events of the 1860s.
32 ACP was also a warhorse for a lot of European countries. Military groups are very hard shells for truly innovative items that don’t make astronomical impact. Like who would have invested in an electronically controlled bomb in 1940... risk it doesn’t work and all that time effort labor and space on the plane for control equipment is a big risk, but an atomic bomb is a game changer weapon. If you look at history in a military procurement frame of mind it’s somewhat amazing that we have advanced as far as we have.... brass cartridge rifles WERE available before the events of the 1860s.
Monac
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West Kentucky wrote: "Why is 32 Semi rimmed? Because JMB as highly regarded as he is did not ever think completely outside of the box. He kicked the box over, stood inside and looked out, but never truthfully stepped out of the box."
When Browning introduced the semi-rim for the 38 ACP and 32 ACP, there were two boxes for pistol cartridges: Rimmed and Bottlenecked. He, as far as I know, invented another box: Semi-Rimmed. Sure, later an even better box named Rimless came along, but Browning's solution was just plain more compatible with the machining technology of the 1890's. Try to think of how many 32 ACP and 25 ACP pistols were sold compared to 7.65mm Luger, 7.63mm Mauser, 9mm Luger, and 45 ACP before war broke out in 1914 and lit a fire under military pistol production. It's not even close. Even an industrially weak and backwards country like Spain could mass produce usable 32 and 25 automatics.
I am having a hard time grappling with the claim that Browning did not ever think outside of the box. True, he did not do anything as fundamental as inventing the percussion cap or the metallic cartridge. But he either invented gas operation for firearms or at least was the first to make it practical, with the Colt-Browning machine gun of 1895. And he patented many of the most practical and economical automatic pistols designs, to the dismay of FN and Colt's competitors everywhere until the 1920's. Things we thing of as very simple, like the basic elements of Colt 1911 or the FN 1910, were outside the box when Browning made them. (I mention the 1910 because, like the 1911, lots of pistols are still being made with that basic design today. Go look at any cheap cast zinc automatic to see what I mean.)
BTW, a small German team began developing the Fritz-X radio-guided bomb in 1938.
When Browning introduced the semi-rim for the 38 ACP and 32 ACP, there were two boxes for pistol cartridges: Rimmed and Bottlenecked. He, as far as I know, invented another box: Semi-Rimmed. Sure, later an even better box named Rimless came along, but Browning's solution was just plain more compatible with the machining technology of the 1890's. Try to think of how many 32 ACP and 25 ACP pistols were sold compared to 7.65mm Luger, 7.63mm Mauser, 9mm Luger, and 45 ACP before war broke out in 1914 and lit a fire under military pistol production. It's not even close. Even an industrially weak and backwards country like Spain could mass produce usable 32 and 25 automatics.
I am having a hard time grappling with the claim that Browning did not ever think outside of the box. True, he did not do anything as fundamental as inventing the percussion cap or the metallic cartridge. But he either invented gas operation for firearms or at least was the first to make it practical, with the Colt-Browning machine gun of 1895. And he patented many of the most practical and economical automatic pistols designs, to the dismay of FN and Colt's competitors everywhere until the 1920's. Things we thing of as very simple, like the basic elements of Colt 1911 or the FN 1910, were outside the box when Browning made them. (I mention the 1910 because, like the 1911, lots of pistols are still being made with that basic design today. Go look at any cheap cast zinc automatic to see what I mean.)
BTW, a small German team began developing the Fritz-X radio-guided bomb in 1938.
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barnetmill
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lysanderxiii
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Bottlenecked cartridges were introduced to allow a larger case volume without making the case ridiculously long. Rimless bottlenecks headspace off the shoulder because that's the only logical place they can headspace.
zaitcev
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Except .357 SIG, which headspaces as if it were .40 S&W.
Jim Watson
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That's the official spec but when it was new on the market, guns before much ammo, I saw small shop stuff in necked down .40. It came out too short to headspace on the mouth, it was shoulder or extractor.
Zaydok Allen
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Cuz JMB screwed up a little. It happens.
Mosin77
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Hollowpoints as we know them didn’t exist in 1899. There was no practical downside to the semi-rim. How many cases of rimlock occur when you’re shooting FMJ? I’ve never experienced a single incidence of it and I’ve shot a pile of .32acp out of perhaps a dozen different handguns. It seems to happen when folks are trying to shoot shorter OAL rounds, like modern hollowpoints. I don’t say rimlock isn’t a real issue, but I do think it’s very overplayed.
Crosshair
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This is exactly the reason.
Today, we are spoiled with consistent and quality brass. We take it for granted. Our designs today assume that case failure is an abnormality.
120 years ago, gun designs had to assume that case failure would be a semi-regular occurance. That's why the 98 Mauser is as over built as it is.
As a kid, I read all sorts of books about early aviation. A recurring theme in the books on WW1 was pilots and crews spending many hours inspecting every individual round of amunition to prevent jams. Even a decade and a half into the 20th century, cartridge technology could not be trusted in autoloading weapons.
This inability to trust the amunition manufacturing technology affected the design of not only the guns, but the cartridges themselves.
lysanderxiii
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Monac
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Browning wasn't perfect. It is very instructive to see how FN of Belgium improved the BAR, for example; there is a good video about that on the "Forgotten Weapons" YouTube channel. But the semi-rim on the 32 ACP was not a screw-up, but a simple, practical answer for the problem at hand. Yes, in the future, people wished it did not have the semi-rim. How was Browning supposed to see that coming? He was helping INVENT the automatic pistol; the immediate problem was to make one that worked well and was practical to manufacture. He did that to the satisfaction of everyone for decades to come.
Mosin77
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...people forget that that “mistake” 7.65 Browning round, made its debut in the first ever pistol with a reciprocating slide. A feature that’s a given on pretty much every single handgun now made. That .32 pistol, which they made some 700,000 of, basically established and defined what a semi-auto handgun should look like and how it should be configured, and, to great extent, how it functions. Within 10 years every new pistol on the market copied it, either broadly or down to the smaller details. And many, perhaps even most, used the same cartridge, too. I don’t necessarily think John Browning was the most brilliant, exalted, or saintly human being to ever walk the earth..... that honor probably goes to Aristotle or St. Thomas Aquinas.... but he designed several dozen more guns, from scratch, than I have, and almost single-handedly gave us the basics of almost all the design elements still used today. Which is a pretty monumental accomplishment in firearms history. I’d think long and hard before labeling any design choice of his a mistake, from the comfort of a computer chair 120 years later.
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