THE 10MM AUTO: Most Versatile Auto Cartridge?

While we often think of the 10mm Auto as a thoroughly modern cartridge, the idea of a powerful mid-bore is not a new one. In fact you could even go as far back as 1874 when the .38-40 Winchester (.38 WCF) was introduced in the Winchester Model 1873 lever-action rifle. Recent factory loading of this cartridge pushed a 180gn, .40 caliber bullet at about 872fps out of a 6-1/2" barrel.  Colt then added the cartridge to their Single Action Army revolver in 1884, providing the round a home in both a lever-action repeater and a handgun.  This concept proved very popular as individuals using this combination would only need to carry one type of ammunition.

Fast-forward a little less than 100 years and you will find another mid-bore powerhouse introduced... the .41 Remington Magnum. Similar in theory to the Bren Ten and 10mm Auto of some 20 years later, the S&W Model 57 and the .41 Magnum was to be the ultimate combat/police handgun and cartridge combination. The idea was to fill the gap between the .357 and .44 Magnums calibers. 

In the early 1970's an individual by the name of Whit Collins started looking at the feasibility of rechambering the 9mm Browning Hi-Power to a more powerful cartridge. Originally he was considering the .38 Super, but Col. Cooper's idea of a 200gn bullet of .400" diameter traveling at 1,000fps changed his thinking. Whit Collins did a lot of work just looking into the feeding geometry to see if a .40 caliber bullet could be made to function. When he was satisfied that it could he began looking for existing rifle cases that had the proper casehead dimensions and could be trimmed down to proper length for the Hi-Power magazine. With his drawings and some "dummy" loads made up he approached Jeff Cooper about his idea. Col. Cooper lent his support to Mr. Collin's idea and with investigative and research help from Guns & Ammo the project moved ahead. Next came assistance from Irv Stone of Bar-Sto and master gunsmith John French and by 1972 a Browning Hi-Power chambered in .40 G&A was being test fired. The loads being fired consisted of a 180gn bullet at 1,050fps out of the 5" barrel. In 1973 Col. Cooper and Mr. Collins started talking about a longer cased .40 caliber round that would be developed with the various .45 Auto platforms in mind. At this point Whit Collins went on to continue working on his .40 G&A and Jeff Cooper began his work on what was being called the .40 Super.

Whit Collins' creation used the .30 Remington case as its parent case, but forming the cases required extensive work.  In addition to this, feeding issues where never totally ironed out.  Because of this the project languished for a number of years until the late 70s when the project was resurrected by the Guns & Ammo staff, including Dr. Ralph C. Glaze.  This time the .224 Weatherby Magnum case was used as a starting point making case conversion and prep work more manageable.  It was also felt that the case's belt would provide more consistent headspacing which they felt was needed to to the cartridge's high performance.

Using another Browning High Power as the shooting platform, Bar-Sto was again enlisted to supply the barrel.  The magazine also needed some modifications, including changing the angle of the follower.  The final product was a 10-shot semiauto capable of firing 180gn bullets at velocities up to 1,260fps!

Jeff Cooper's concept of the .40 Super didn't make much headway until two individuals sought his input for a new combat pistol they were planning to manufacture and market as a replacement for the venerable 1911.  With Col. Cooper's help, and blessing, Tom Dornaus and Mike Dixon introduced the shooting world to the 10mm Auto.

Having a design for a superior handgun cartridge is only the first step, however. A far trickier endeavor is convincing an established manufacturer to mass produce and market your new round. This job fell to Mike Dixon who encountered numerous frustrations trying to talk ammo makers into producing ammo for a gun that didn't even exist yet.  Dixon contacted numerous ammunition manufactureres, and unsurprisingly most were uninterested.  At one point Dornaus & Dixon reported that Hornady had agreed to produce the ammo, but this never came to pass.  (It was Hornady that, following Colt's introduction of the Delta Elite, eventually took the 10mm to SAAMI for official approval.)

In 1983, after numerous disappointments, Norma of Sweden finally agreed to produce the new round. Like the .41 Magnum, it was to be initially offered in two loadings. The first was a 170gn JHP at 1,300fps for maximum stopping power, and second, a 200gn JTC at 1,200fps for deep penetration. These loads both produced over 600 ft lbs of energy and were significantly more powerful than Col. Cooper's 200gn .40 caliber projectile at 1,000fps!

When discussing the F.B.I.'s adoption of the 10mm Auto it is necessary to start with the event that shocked the agency into reevaluating what it armed it's agents with.  This, of course, is the infamous 1986 Miami shootout.  In short, the F.B.I. had been on the trail of two individuals suspected of murder and armed bank robbery.  In the final confrontation eight agents performed a 'felony stop' of the suspects' car.  During the ensuing gunbattle both individuals were mortally wounded, but were still able to kill two agents and seriously wound five others.  In the subsequent investigation one of primary findings was that the 9mm ammunition used by some of the agents failed to penetrate deeply enough and were therefore unable to incapacitate the two suspects quickly.

https://en.wikipedia.org/wiki/1986_FBI_Miami_shootout

At the time jacketed hollowpoint technology was still relatively new, but rather than push for better performing 9mm ammunition the F.B.I. decided a better fix would be the adoption of a new cartridge.  It is rumored that the F.B.I. had basically decided that it wanted the .45 ACP, but in order to justify the expense of rearming all their agents with new guns and ammo they would need to go through extensive testing protocals.  In order to not appear biased in favor of the .45 before the testing even began, it was decided that the new 10mm Auto cartridge would be added to the list.

In the early 1970's an individual by the name of Whit Collins started looking at the feasibility of rechambering the 9mm Browning Hi-Power to a more powerful cartridge. Originally he was considering the .38 Super, but Col. Cooper's idea of a 200gn bullet of .400" diameter traveling at 1,000fps changed his thinking. Whit Collins did a lot of work just looking into the feeding geometry to see if a .40 caliber bullet could be made to function. When he was satisfied that it could he began looking for existing rifle cases that had the proper casehead dimensions and could be trimmed down to proper length for the Hi-Power magazine. With his drawings and some "dummy" loads made up he approached Jeff Cooper about his idea. Col. Cooper lent his support to Mr. Collin's idea and with investigative and research help from Guns & Ammo the project moved ahead. Next came assistance from Irv Stone of Bar-Sto and master gunsmith John French and by 1972 a Browning Hi-Power chambered in .40 G&A was being test fired. The loads being fired consisted of a 180gn bullet at 1,050fps out of the 5" barrel. In 1973 Col. Cooper and Mr. Collins started talking about a longer cased .40 caliber round that would be developed with the various .45 Auto platforms in mind. At this point Whit Collins went on to continue working on his .40 G&A and Jeff Cooper began his work on what was being called the .40 Super.