Today, I want to talk about two modern cartridges, the 40 S&W and the 10mm. They had some very publicly documented development, that somehow also became one of the most widely misquoted or understood origin stories (that I, too, have been guilty of repeating). Part of the confusion comes from the accounts documenting the cartridges. Nearly every writer provides a different version of the events, decisions, and people involved in the journey. So, we're going to take a look at where they actually came from, and how an idea that lingered nearly a century finally became a production reality. And remember: if you think I'm wrong, fight me in the comments; if you can prove I'm wrong, shoot me an email, I'd love to hear from you.

.40 caliber was rare throughout most of the black powder era. It wasn't until the early 1800s, as percussion caps were replacing the flintlock, that it found a home in rifles on the American frontier. However, as breechloading and cartridges evolved, it took a back seat to the much more popular .45 caliber. By the time .40 caliber regained it's foothold, cartridges were most often made from necked-down 45 cases. By the mid-late 1800s it could be found in everything from the tiny .41 Rimfire, to the 450-400 Express. The 41 pistol cartridges, most commonly having an actual diameter between .401" and .406", saw a modest popularity among lawmen and gunfighters, who praised it's short-range capability. Colt's 41 Long, originally firing a .403"-.406" 200gr bullet at 750fps, would follow the same route as many other pistol cartridges of the era and end up with slightly under-caliber bullet at .386" in 1889 when heeled bullets were replaced by the inside lubricated type. 

On the other side of things was the popular 38 WCF, more commonly known as 38-40, which was designed with an inside lubricated bullet. The reasoning behind the 38 nomenclature is unknown, as bullets were .401" in diameter. It appears to have been a marketing decision by Winchester that other manufacturers simply followed. It was introduced as a rifle cartridge around 1874 in the Winchester Model 1873, and later about 1884 in the Colt Model P. In the revolver, 38-40 offered slightly improved ballistics to the 41 Long Colt, firing a 180gr bullet at an average of 800fps out of the 4-7" barrel. The disparity increased slightly as Colt switched the 41 Long to .386" hollow base bullets, as they used barrels with the same .400"/.406" bore diameter. The bottle-neck cartridge, however, was not ideal for use in a revolver, as cases would stretch under firing and could bind the cylinder.

During the early 1900s, while Smith & Wesson was taking advantage of smokeless powders to improve cartridge performance and release higher velocity "Special" cartridges, Colt focused on their military contracts and marginal cartridges like the 41 were largely ignored. This might seem neglectful on Colt's part, but it must be remembered that early smokeless powders were often inconsistent or unreliable, leading even professional shooters to stick with black powder loads well into the 1920s. 

Early automatic pistols also experimented with .40 caliber cartridges, like the 10mm Bergmann and 10mm Mars. On the occasion that these early pistols and ammunition actually functioned, more often than not, the designs and metallurgy were not able to handle the cartridges, and none managed to secure military contracts. The same was true of Colt's 41 Automatic, which was actually .386". Colt's cartridge would evolve into the 9.8mm Automatic and 9.65mm Browning and was about the closest that an automatic cartridge bridging the gap between 38 and 45 caliber got to mass production before WWI. The war, and it's aftermath, would prevent these, and later cartridges like the .39 BSA, from ever seeing full scale production. With the surplus of 9mm and .45 caliber pistols and ammunition, it wouldn't be until after the second world war that manufacturers or militaries would seriously consider production of other calibers in a service automatic. In the meantime, the 40 caliber revolver cartridge kept evolving.

Winchester would modernize their rifle cartridge around 1910 with the introduction of the 401 Self Loading, a straight-walled semi-rimmed cartridge firing a .406" 200 or 250gr bullet.

By the 1920s the quest for speed was being undertaken by enthusiasts more often than established manufacturers. Gunsmiths and handloaders were improving the performance of the 38-40, combined with the reliability of a straight-walled cartridge by trimming down 401 SL brass. One of the most noted of these was Missouri gunsmith Cyril Eimer, known as "Pop". He would trim cases to 1.25", use 200gr 38-40 bullets, and DuPont Pistol Powder No.3 for a velocity between 900-1000fps. Model 1873 cylinders would be rechambered for the cartridge, known as 40 Eimer Special, and by contemporary accounts proved to be an accurate load with no more recoil than standard 38-40.

Eimer's work would catch the attention of Colt "ambassador" John Fitzgerald. Better known as Fitz, he was the longtime public face of the company, being one of the most well known salesmen and representatives in the country. Fitz would take the idea to Colt's factory Superintendent Fred Moore. In 1932 Moore experimented with improving the 41 Long Colt for use in Official Police and New Service revolvers. The resulting cartridge, with sample lots produced by Remington-UMC, used a lengthened 41 case and a .386" 210gr bullet for a velocity of 1150fps. At the time, no one could predict just how popular such a cartridge would turn out. When S&W released the .357 Magnum three years later they had projected moderate sales, but demand quickly ran so high that production would take several years to meet it.

During the 1940s another gunsmith became known for his work with the 40 caliber; Gordon Boser, of New York. He also shortened 401 SL cases, but designed his own bullets, most notably a 195gr semi wadcutter offered with Lyman as a bullet mold (No. 410452). A later Herters 401 Magnum would be nearly identical to the 401 Boser Special. 

By the 1950s the Magnum era was well at hand, and few were more vocally or physically supportive of the concept than outdoorsman and gun writer Elmer Keith. He had a hand in the development of the 357 and 44 Magnum and, together with fellow enthusiasts Bill Jordan and Charles Skelton, promoted the idea of a 40/41 Special. They recommended the cartridge be chambered in the S&W K-frame with a 210gr bullet at 900fps for police and self defense use and a velocity of 1400fps for hunting. Another firearms expert, gun writer, and magnum proponent, Jeff Cooper, also espoused the potential of a .40 caliber handgun cartridge. Cooper, formerly a Maj. in the U.S. Marine Corps, was an ardent user and champion of the automatic service pistol. He described the use of a .40 caliber 200gr bullet at 1000fps as the ideal personal defense cartridge. For the time being, both of these were just ideas.

In 1963 Smith & Wesson management took up the call from Keith, Jordan, and Skelton, but decided that more was better, and would partner with Remington to release the 41 Remington Magnum in the N-frame revolver, the same used for the 44 Magnum. Smith & Wesson's decision would cripple sales of the cartridge. With a minimum velocity of 1200fps, it was too much recoil in too heavy a pistol for police use. For hunting, it provided few, if any, advantages over the 44 Magnum, which was cheaper and more widely available.

It wasn't until the mid 1960s that the .40 caliber returned to the automatic pistol. This was done by another firearms expert and prolific gun writer, George Nonte, retired Major of the U.S. Ordnance Department. He used the 41 Rem Mag case, trimmed it down, rebated the rim and cut an extractor groove to work with a 9mm breechface. It is unclear what load he used or in which pistols it was chambered. Ultimately, his project which required a significant amount of machining would be limited to personal experiments.

In the 1970s Whit Collins, editor at Guns & Ammo Magazine, picked up on Nonte's project and continued development of the concept, presumably under the funding of the Magazine. Collins ditched the 41 cases and instead used brass from 30 Remington. Jeff Cooper joined the project, though his capacity and contributions are unclear. The cartridge and pistol created for the project were featured in a two part article in the magazine during 1972. 30 Rem cases were trimmed down to .866" and reamed to accept a 180gr 38-40 bullet. The cartridge, dubbed 40 G&A after the magazine, achieved a velocity around 1000fps out of the High Power pistol modified by gunsmith John French which included a custom 5" BarSto barrel. Collins and Cooper continued to collaborate on the project and made a higher velocity version, again featured in a 1977 edition of Guns & Ammo magazine. The 40 G&A Magnum was formed by trimming the belted .224 Wetherby Magnum case to the same .866" length and using a 180gr bullet. The magnum pushed velocity up to 1200fps. 

Also during the 1970s, the International Practical Shooting Confederation was created to support the growing competitive shooting market and move away from the static, single-handed, bullseye-type competitions. One of the founding members was Jeff Cooper. The organization would prove to be a breeding ground for product innovation, not only among it's members, but also the manufacturers that supported it. 

Through the late 1970s and early 1980s Whit Collins and Jeff Cooper took the 40 caliber project in two different directions. 

Cooper envisioned a more powerful cartridge for use in a full size pistol, which he referred to as 40 Super. At the same time, two IPSC members were working to modernize the American service pistol. Tom Dornaus, gunsmith with Pachmayr Gun Works, and Mike Dixon, with a background in aerospace manufacturing and law enforcement, were former coworkers and in 1979 partnered to produce a 45 caliber pistol based on the CZ-75. While the prototype Combat Service Pistol was taking shape, Tom and Mike reached out to Jeff Cooper to consult on the project. In August 1980 Cooper debuted the pistol prototype at the IPSC Nationals. By 1981, under Cooper's influence, it was decided that the pistol would be produced in the 40 Super cartridge. According to most sources it was also Cooper who named both the Bren Ten pistol, and the 10mm cartridge. Sources conflict on exactly when and by whom cartridge development took place. It appears that cartridge prototypes were made by John Connelly, under the direction of Mike Dixon, who essentially just lengthened Collin's 40 G&A during experiments to find the best case length for reliable feeding. Around 200 prototype cases were made, and velocity of 200gr bullets, supplied by Sierra, reached 1150fps. It wasn't until 1983 that a manufacturer willing to produce cartridges for a pistol that didn't exist yet was found with the Swedish firm Norma. Norma developed a new powder specifically for the cartridge and 200gr fully jacketed truncated-cone bullets reached a velocity just over 1200fps. A 170gr jacketed hollow-point was also offered with a velocity of 1300fps. Developing both a new firearm and a new cartridge proved too ambitious for the small company however, which was plagued by constant lack of funding and would produce less than 1500 pistols before going out of business in 1986. 

Whit Collins' work on the 40 G&A had inspired Smith & Wesson employees Tom Campbell, Richard Baker, and Norman Spencer. Baker, then Senior Project Engineer, is generally credited as the driving force behind the project and signed off on the cartridge and pistol prototype blueprints. Spencer was a model maker, which is to say an expert machinist, and did nearly all of the physical machining to produce the cartridges, barrel, and the required tooling. Campbell was also a model maker and test technician, as well as an avid shooting competitor.  Baker and Spencer essentially retraced George Nonte's work, creating a 9mm-lenght, rebated rim cartridge from 41 Magnum brass. 180gr 38-40 bullets were used with 5-7gr of Unique powder, though no velocity testing is documented. With the help of several others, they managed to sneak some custom tooling into the production line and produced two .40 caliber barrels for the Model 59 pistol. The first prototype pistol and ammunition were fired April, 28 1978 by Tom Campbell. With additional testing, a functional magazine was created and the conclusion was reached that a heavier slide would be required. Nonetheless, blueprints were made for the cartridge and barrel prototypes, as well as recommendations for changes to the pistol and of a more standard cartridge without a rebated rim. The prototypes would be marked 40 B&S (Baker and Spencer) to stake their claim on the project, however, all blueprints were marked 40 S&W. After all, the whole point was to pitch the project to management. In May 1978 Baker took the cartridge blueprints to a friend at the Olin Corporation to see if Winchester would be able and willing to produce the cartridge. With affirmation that cartridges could be produced, he then took the whole project to Smith & Wesson executives. It was summarily rejected by the Marketing Department and the project was abandoned. Frankly, this may have been for the best. At the time, Smith & Wesson executives were so focused on cutting costs that quality suffered and they nearly drove the company into bankruptcy before it was sold in 1984. Baker would retire in 1986, leaving behind the prototypes, tooling, and blueprints.

Meanwhile, Whit Collins approached Pachmayr Gun Works. Pachmayr considered producing Collin's cartridge as the 10mm PGW, with the aim to dethrone the 38 Super in Practical Shooting Competition. Pachmayr would ultimately decline to produce the cartridge. However, Collins continued to promote it. After Norma began producing 10mm Auto in 1983 Collins simply trimmed the cases for his own cartridge, rather than using 30 Rem brass, and the name was changed to Centimeter. Also in 1983 South African gunsmith and competitive shooter Paul Liebenberg moved to the US and went to work for Pachmayr. One of his projects was adapting the 1911 platform for the Centimeter cartridge. Pachmayr began moving away from producing custom pistols, and Liebenberg left in 1986 to start his own company Pistol Dynamics. Collins and Liebenberg would continue to collaborate on the cartridge as Liebenberg produced custom competition pistols, using barrels from BarSto. One of the men using such a pistol was Tom Campbell. Bud Watson, of Watson Precision produced ammunition. Eventually the fact that Campbell was winning matches under the banner of Smith & Wesson, without using a S&W pistol came to the attention of company President Steve Melvin. Melvin presented the project of chambering the 5906 pistol in the Centimeter cartridge to the Advanced Product Dept., who laid it out in CAD software and declared it impossible. Melvin was undeterred and contracted Pistol Dynamics to modify two S&W pistols. They were completed and sent to S&W engineers, where one was immediately "misplaced". 

While the Centimeter was rising among competitive shooters, in 1987 the 10mm Auto had found a new home in a Colt 1911, the Delta Elite. This gave domestic manufacturers the confidence to also begin producing the 10mm Auto cartridge. 

Another fateful event occurred the year prior with the infamous 1986 FBI Miami Shootout. During the engagement, two bank robbers, and multiple murderers, armed with .357 revolvers, a pump action shotgun, and a Mini-14 rifle, were confronted by 8 FBI agents hunting them. While other agents in the area were carrying AR-15s and MP5s, the agents involved with the engagement were only able to bear 1 Remington 870 shotgun, 3 S&W 14-shot 9mm's, a handful of .357 revolvers, and 2 38 special snub-nose revolvers. Two of the agents involved had bullet-proof vests, but they were not rated for 223 rifle rounds. Objectively speaking, the shootout was a complete failure of preparation and marksmanship by the FBI. The suspects were spotted while driving and as they fled, 3 FBI vehicles rammed the suspect vehicle, which was forced off the road into a residential driveway where one FBI vehicle and the suspect's vehicle drove into a tree and were disabled. The suspects opened fire, as other FBI vehicles were brought into position for cover and engagement. During the initial contact one agent lost his service pistol and was left with only a 5 shot 38 Special revolver, another was left completely unarmed, two FBI vehicles were disabled, and one shotgun sat in a trunk sat in a trunk during the entire engagement. The only agent able to retrieve a shotgun from his vehicle was shot in the forearm and struggled to fire it single handed throughout the 5 minute engagement. At one point a single man with a semi-automatic rifle was able to suppress at least 5 agents, killing two and seriously injuring another while they were attempting to reload behind cover. The two suspects were shot a total of 6 and 12 times. Though both had received fatal wounds within the first few minutes of the gunfight, none proved to be immediately incapacitating until one man was shot in the head multiple times and the other the spine, both at close range with a .357 Magnum.
Following the incident, the FBI began reevaluating their training protocols, however, the media immediately latched on to the headline that the FBI and police were outgunned. While this was certainly true to a degree, it created a bigger issue in that law enforcement agencies throughout the country faced a crisis of confidence. The slow trickle of departments and individuals switching from revolvers to automatics increased dramatically and was divided between those who wanted more rounds in a 9mm or a bigger cartridge in the 45. The FBI scheduled testing and repeated the same 36 versus 45 caliber debate that has been ongoing since about 1850. The Head of the FBI's Firearms Training Unit is quoted as saying "All other things aside, Miami was an ammunition failure." And his assistant espousing that "there was no meaningful ammunition testing prior to 1988". For testing cartridges, they dismissed the possibility of overpenetration because "[8 out of 10] rounds fired by law enforcement officers engaged in violent encounters do not strike the intended targets". 
The 1988 FBI ammunition tests were certainly among the first to set a consistent and measurable standard by which ammunition was judged. That standard was a minimum of 12" of penetration in 10% ballistic gel, including after a bullet passed through certain barriers. A last minute addition to the tests was the inclusion of 10mm in a Colt Delta Elite pistol. The initial tests showed that 185gr 45 ACP at 950fps met the standard to nearly the same degree as did the Norma 170gr 10mm, which preformed the best during testing. However, everyone that fired the 10mm agreed that recoil and muzzle blast were excessive. The test board then hand loaded 180gr bullets in 10mm cases for a 950fps velocity to match the 45. Additional testing showed that all three cartridges met the FBI standard to a nearly identical degree. This testing has seen the same measure of controversy and blind acceptance as the 1904 Ordnance Dept. tests. It should be pointed out, however, that apart from the 10mm only ammunition already issued by the FBI was tested, and that the FBI was adamant upon disclosing their findings that their goal was not to find the ideal police bullet, but rather "to learn what rounds had the highest probability of success under the conditions determined appropriate for the FBI's needs." The 10mm was officially announced as the FBI's new cartridge in 1989. This decision was not without its own controversy, the head of the Firearms Training Unit publicly declared that 9mm and 45acp were old and had no further development potential, while privately confiding that he couldn't request funding from congress for a 45 caliber pistol when the US Military had just switched to 9mm. The reality of the situation was that the currently issued Sig P220 would have met all the FBI's new standards, but the 10mm lite was chosen as a compromise to meet the concerns of those who wanted higher capacity and those who wanted 45 ACP performance. 
In 1989 the FBI contracted with Federal for 100,000 rounds of the 10mm lite cartridge, and with Smith & Wesson for 9,500 units of a new 10mm handgun, the Model 1076.

Meanwhile, the project to chamber the Centimeter cartridge in the 5906 had been successful and another new model began production setup, the 4006. Contracts to produce the Centimeter cartridge fell through, with rumors of Smith & Wesson objecting to royalty fees demanded by Collins. The truth is probably a bit more complicated. Those backing the Centimeter cartridge had expected it to be marketed as a competition round. Smith & Wesson saw a different opportunity. Knowing about the FBI's 10mm lite, and seeing the sales potential a 9mm-sized gun firing a ballistically identical cartridge would have with police departments, Smith & Wesson contracted with Winchester for the production of the 40 S&W, which was just a slightly shorter version of the Centimeter. The new cartridge and pistol were debuted at the 1990 SHOT Show. It is rumored that Gaston Glock himself not only attended, debuting the new 10mm Glock 20, but also personally stole several 40 S&W sample cartridges from the display booth. Upon seeing that the Glock 17 could fire the cartridge with little more than a barrel change, Glock immediately began designing what would be the Model 22. In fact, Glock was able to produce and distribute the Model 22 about a week before Smith & Wesson 4006 pistols began shipment for distribution themselves. While this likely didn't effect sales, it was an embarrassment for Smith & Wesson who had long underestimated the Austrian firm. The debut of the 40 S&W cartridge was also painfully awkward for the FBI. It was the embodiment of what they had wanted, but they found themselves in possession of 100,000 rounds of 10mm ammunition and stuck in a contract for pistols that were unnecessarily large and unnecessarily heavy with a lower capacity than the 4006. As the contract pistols began to come in, the FBI spared no opportunity to remark on defects and return pistols back to S&W for repair. In 1993, with only around 2400 model 1076 pistols produced, S&W and the FBI dissolved their contract. After another lengthy and bureaucratic selection process, the FBI adopted the 40 S&W in 1997, along with the Glock Model 22. 

As the 40 S&W rose to become the standard cartridge among law enforcement agencies throughout the US, the 10mm nearly faded into obscurity as a niche handgun hunting round. Around the mid 2010s, however, their fates began to change. The 10mm saw a resurgence of interest as a versatile, multi-purpose cartridge and the 40 S&W began being replaced in the service pistol once again by the 9mm. 

The story of the 40 caliber cartridge is something of an ironic one. Since 1800, it has been introduced and fallen out of favor about every 40 years, with each new iteration being touted as the modern incarnation of the ideal cartridge. The 40 caliber automatic is no exception.