The 10mm Auto
10mm Auto (or 10x25mm) is a handgun cartridge that uses a .40 calibre
bullet. .40 calibre cartridges were once fairly popular alternatives to
.44 or .45 rounds and their smaller .36 or .38 calibre brethren. For
some reason they fell out of favour about the same time that smokeless
powder became dominant. About the only .40 calibre round I can bring to
mind that managed to live well into the smokeless-powder era is the old
.38-40 Winchester -- and it was hard to find in stores until the
upswell in Cowboy Action Shooting as a sport.
Regardless of the
historical background there were good reasons to make a .40 calibre
handgun round -- especially one that was designed to be used in
autopistols. The absolute exterior dimensions of 10mm cartridge cases
make double-stack, high-capacity magazines for them practical... at
least for most people with average-sized hands. This meant that one
could design a high-capacity handgun for a cartridge that had
significantly higher power than the widely-used 9mm Parabellum.
Browning actually was working on a .40 calibre round and a pistol to
match when he was diverted into other projects by his employers. That
pistol, by the way, eventually was designed around the 9mm Parabellum
round and finally became the famous "Browning Hi-Power" or "P-35" as it
was also known.
Moving forward in time to the mid-1970s.
Militaries around the world had adopted semi-auto handguns as sidearms
with great success. Most countries used the 9x19 NATO round. The USA
was still using the .45 ACP round. Police departments across America
were beginning to switch from Double-Action revolvers to semi-auto
pistols in either .45 ACP or 9mm NATO. Combat Pistol shooting (as it
was called back then) was becoming very popular. The rules of the game
gave a scoring benefit to any round that had a "Power Factor" (actually
a measure of momentum, not power) that was equal to or greater than a
standard .45 ACP using the common 230 grain ball (aka:
full-metal-jacketed) ammunition. The 9mm was not able to gain that
scoring advantage, but it did have a capacity advantage over the 7 or 8
rounds that the popular model 1911 in .45 ACP held. Competitors, being
-- well, competitive -- wanted both in one pistol. They "re-discovered"
the old .38 Super Automatic cartridge and had a significant degree of
success with it -- and some problems as well. The search for a "better"
Col. Jeff Cooper was a founder of these
Combat Pistol matches. He was a .45 ACP advocate and a 1911 booster as
well. But Col. Cooper's mind was open to better ideas -- they just had
to be proven to his satisfaction. He and some of his friends came up
with the idea of a .40 calibre cartridge that would fit and function
through a standard 1911 pistol. This would allow a couple more rounds
to be carried in the magazine, but without lowering the power to 9x19
levels. What he came up with (and he was not alone in this) was a
straight-walled brass case with a 10mm diameter and a 25mm length. The
prototypes were made from cut-down .30 Remington rifle brass (itself
almost totally obsolete and very hard-to-find) and bullets originally
intended for the old .38-40 Winchester.
A small company in
Southern California called Dornaus & Dixon (D&D) got into the
act as well as the Norma ammunition company in Sweden. D&D started
designing a pistol based on the well-regarded CZ-75 design but
scaled-up to fit the larger ammunition. They called this pistol the
"Bren-Ten" and I actually -- almost -- bought one of the first ones. I
paid a 50% deposit on one of the more expensive models (but not the
MOST expensive!) but D&D went under before I ever saw my pistol.
Norma made the first batch of ammo and it was rated as propelling a 200
grain projectile at 1200 feet per second out of a 5" test barrel. That
was impressive. This new round had MORE power than the .45 ACP and the
cartridge was smaller allowing more rounds to be carried in the
magazine. Things were looking good for the 10mm, but it was a slow,
uphill battle for acceptance. With the demise of D&D things started
looking bad indeed.
Then came the infamous Miami Shootout of 1986.
The details of the shootout are well-researched and available on the net in many places. I won't try to tell all about it here.
this event the FBI decided that they needed an autopistol with more
power and penetration than the 9mm Parabellum pistols that they had
been using. For one reason or another they did not want to go to the
.45 ACP. The 10mm was selected, and it performed brilliantly and this
gave new life to a great round that was almost dead before it ever got
Alas, nothing ever goes easily. Agents were complaining
about the recoil of the 10mm pistols. Their qualifying scores were also
falling. No question about it, the 10mm is more difficult to shoot well
than a 9x19. So the FBI decided to have the ammo makers "download" the
10mm to reduce the recoil (rather than spend the time and money to
train their agents how to shoot a 10mm well). This load became known as
the "FBI Lite" load. This light load became pretty much the de-facto
standard factory load for the 10mm and all but killed interest in it.
recently there has been an upswell of interest in full-power 10mm
rounds. The .40 S&W has taken the place of the 10mm "FBI Lite"
loads and left the 10mm to those who actually want a real 10mm Auto.
More gun makers are making new guns chambered for the 10mm Auto. It is
a great round that simply refuses to die.
The 10mm Auto is a
superb self-defense cartridge as long as the shooter can handle the
recoil. For defensive use, I prefer the mid-weight bullets of 150 to
155 grains. There is also a lot to be said about using the 135 grain
JHP bullets for defensive use, as they do not penetrate so much as the
heavier slugs do. Of course significant penetration is required. It is
always a balancing act and entire books have been written on terminal
ballistics. Any way you look at it, a 135 grain JHP travelling at 1550
feet per second (that's measured with my chronograph and it's over 700
foot-pounds of energy) out of a 3.6" barrel will get any bad guy's
attention if you hit him with it. Misses don't count.
heavier bullets of 200 grains and up it has served as a hunting
cartridge and does as well as many highly-regarded revolver rounds.
This is one of my two top favourite autopistol rounds.
It will do just about anything you can ask of it except recoil softly or become extinct.